THE SKULL
THE INFERIOR MAXILLARY BONE
The Inferior Maxillary Bone, the largest and strongest bone of the face, serves for the reception of the inferior teeth. It consists of a curved horizontal portion, the body, and of two perpendicular portions, the rami, which join the former nearly at right angles behind.
The Horizontal portion, or body, is convex in its general outline, and curvedsomewhat like a horse-shoe. It presents for examination two surfaces and two borders. The External Surface is convex from side to side, concave from above downwards. In the median line is a well marked vertical ridge, the sym-physis; it extends from the upper to the lower border of the bone, and indicates the point of junction of the two pieces of which the bone is composed at an early period of life.
Inferior Maxillary Bone, Outer Surface, Side View
The lower part of the ridge terminates in a prominent triangular eminence, the mental process. On either side of the symphysis, just below the roots of the incisor teeth, is a depression, the incisive fossa, for the attachment of the Levator menti; and still more externally, a foramen, the mental foramen, for the passage of the mental nerve and artery. This foramen is placed just below the root of the second bicuspid tooth. Running outwards from the base of the mental process on each side, is a well marked ridge, the external oblique line. This ridge is at first nearly horizontal, but afterwards inclines upwards and backwards, and is continuous with the anterior border of the ramus; it affords attachment to the Depressor labii inferioris and Depressor anguli oris, below it, to the Platysma myoides.
The Internal Surface is concave from side to side, convex from above downwards. In the middle line is an indistinct linear depression, corresponding to the symphysis externally; on either side of this depression, just below its centre, are four prominent tubercles, placed in pairs, two above and two below; they are called the genial tubercles, and afford attachment, the upper pair to the Genio-hyo-glossi muscles, the lower pair to the Genio-hyodei muscles. Sometimes the tubercles on each side are blended into one, or they all unite into an irregular eminence of bone, or nothing but an irregularity may be seen on the surface of the bone at this part. On either side of the genial tubercles is an oval depression, the sublingual fossa, for lodging the sublingual gland; and beneath it a rough depression on each side, which gives attachment to the anterior belly of the Digastric muscle. At the back part of the sublingual fossa, the internal oblique line (mylo-hyoidean) commences; it is faintly marked at its commencement, but becomes more distinct as it passes upwards and outwards, and is especially prominent opposite the two last molar teeth; it divides the lateral surface of the bone into two portions, and affords attachment throughout its whole extent to the Mylo-hyoid muscle, the Superior constrictor being attached abova its posterior extremity, nearer the alveolar margin. The portion of bone above this ridge is smooth, and covered by the mucous membrane of the mouth; whilst that below it presents an oblong depression, wider behind than in front, the submaxillary fossa, for the lodgment of the submaxillary gland. The superior or alveolar border is wider, and its margins thicker behind than in front. It is hollowed into numerous cavities, for the reception of the teeth; these are sixteen in number, and vary in depth and size according to the teeth which they contain. At an early period of life, before the eruption of the teeth, the alveolar process is proportionally larger and deeper than in the adult, and the chief part of the body is above the oblique line. In adult life the base of the bone attains its maximum of development. In old age, on the contrary, after the loss of the teeth, the alveolar process becomes absorbed, and the chief part of the body is that which exists below the oblique line. At this period, the dental canal and mental foramen are situated close to the upper border of the bone. The inferior border, longer than the superior, and thicker in front than behind, is rounded; it presents a shallow groove, just where the body joins the ramus, over which the facial artery turns.
Inferior Maxillary Bone, Inner Surface, Side View
The Perpendicular Portions, or Kami, are of a quadrilateral form, and differ in their direction at various periods of life. In the foetus, they are almost parallel with the body; in youth they are oblique; in manhood they are nearly vertical, joining the body at almost a right angle. In old age, after the loss of the teeth, they again decline and assume an oblique direction. Each ramus presents for examination two surfaces, four borders, and two processes. The external surface is flat, marked with ridges, and gives attachment throughout nearly the whole of its extent to the Masseter muscle. The internal surface presents about its centre the oblique aperture of the inferior dental canal, for the passage of the inferior dental vessels and nerve. The margins of this opening are irregular, and present in front a prominent ridge, surmounted by a sharp spine, which gives attachment to the internal lateral ligament of the lower jaw; and at its lower and back part is seen a notch leading to a groove, which runs obliquely downwards to the posterior extremity of the submaxillary fossa; this groove is the mylo-hyoidean, and lodges the mylo-hyoid vessels and nerve; behind the groove is a rough surface, for the insertion of the Internal pterygoid muscle. The inferior dental canal descends obliquely downwards and forwards in the substance of the ramus, and then horizontally forwards in the body; it is here placed under the alveoli, with which it communicates by small openings. On arriving at the incisor teeth, it turns back to communicate with the mental foramen, giving off two small canals, which run forward, to be lost in the cancellous tissue of the bone beneath the incisor teeth. This canal, in the posterior two-thirds of the bone, runs nearest the internal surface of the jaw; and in the anterior third, nearer its external surface. Its walls are composed of compact tissue at either extremity, cancellous in the centre. It contains the inferior dental vessels and nerve, from which branches are distributed to the teeth through the small apertures at the bases of the alveoli. The superior border is thin, and presents two processes, separated by a deep concavity, the sigmoid notch. Of these processes, the anterior is the coronoid, the posterior the condyloid.
The Coronoid Process is a thin, flattened, triangular eminence of bone, which varies in length in different subjects. Its external surface is smooth, and affords attachment to the masseter and temporal muscles. Its internal surface gives attachment to the temporal muscle, and presents the commencement of a longitudinal ridge, which is continued to the posterior part of the alveolar process. In front of this ridge is a deep groove, continued below on to the outer side of the alveolar process; this ridge and part of the groove afford attachment above to the Temporal, below to the Buccinator muscle.
The Condyloid Process, shorter but thicker than the coronoid, consists of two portions; the condyle, and the constricted portion which supports the condyle, the neck. The condyle is of an oval form, its long axis being transverse, and placed in such a manner that its outer end is a little more forward and a little higher than its inner. It is convex from before backwards, and from side to side, the articular surface extending further on the posterior than on the anterior surface. The neck of the condyle is flattened from before backwards. Its posterior surface is convex; its anterior is hollowed out on its inner side by a depression (the pterygoid fossa), for the attachment of the External pterygoid. The lower border of the ramus is thick, straight, and continuous with the body of the bone. At its junction with the posterior border is the angle of the jaw, which is somewhat everted, rough on each side for the attachment of the masseter externally, and the internal pterygoid internally, and, between them, serving for the attachment of the stylo-maxillary ligament. The anterior border is thin above, thicker below, and continuous with the external oblique line. The posterior border is thick, smooth, and rounded, and covered by the parotid gland.
The Sigmoid Notch, separating the two processes, is a deep semilunar depression, crossed by the masseteric artery and nerve.
Development. This bone is formed at such an early period of life, before, indeed, any other bone excepting the clavicle, that it has been found impossible at present to determine its earliest condition. It appears probable, however, that it is developed by two centres, one for each lateral half, the two segments meeting at the symphysis, where they become united. Additional centres have also been described for the coronoid process, the condyle, the angle, and the thin plate of bone, which forms the inner side of the alveolus. At birth it consists of two lateral halves. These join at the symphysis at the end of the first year; but a trace of separation at their upper part is seen at the commencement of the second year.
Articulations. With the glenoid fossa of the two temporal bones.
Attachment of Muscles. By its external surface, commencing at the symphysis, and proceeding backwards; Levator menti, Depressor labii inferioris, Depressor anguli oris, Platysma myoides, Buccinator, Masseter. By its internal surface, commencing at the same point; Genio-hyo-glossus, Genio-hyoideus, Mylo-hyoideus, Digastric, Superior constrictor, Temporal, Internal pterygoid, External pterygoid.
ARTICULATIONS OF THE CRANIAL BONES
The bones of the cranium and face, are connected to each other by means of sutures. The Cranial Sutures may be divided into three sets: i. Those of the vertex of the skull. 2. Those at the side of the skull. 3. Those at the base.
The sutures at the vertex of the skull are three, the sagittal, coronal, and lambdoid.
The Sagittal Suture (sagitta, an arrow) is formed by the junction of the two parietal bones, and extends from the middle of the frontal bone, backwards to the superior angle of the occipital. In childhood, and occasionally in the adult, when the two halves of the frontal bone are not united, it is continued forwards to the root of the nose. This suture sometimes presents, near its posterior extremity, the parietal foramen on each side; and in front, where it joins the coronal suture, a space is occasionally left, which encloses a large Wormian bone.
The Coronal Suture extends transversely across the vertex of the skull, and connects the frontal with the parietal bones. It commences at the extremity of the great wing of the sphenoid on one side, and terminates at the same point on the opposite side. The dentations of this suture are more marked at the sides than at the summit, and are so constructed that the frontal rests on the parietal above, whilst laterally the parietal supports the frontal.
The Lambdoid Suture, so called from its resemblance to the Greek letter X, connects the occipital with the parietal bones. It commences on each side at the angle of the mastoid portion of the temporal bone, and inclines upwards to the end of the sagittal suture. The dentations of this suture are very deep and distinct, and are often interrupted by several small Wormian bones.
The sutures at the side of the skull are also three in number; the spheno-parietal, squamo-parietal, and masto-parietal. They are subdivisions of a single suture, formed between the lower border of the parietal, and the temporal and sphenoid bones, and extending from the lower end of the lambdoid suture behind, to the lower end of the coronal suture in front.
The Spheno-parietal is very short, and formed by the tip of the great wing of the sphenoid, and the anterior inferior angle of the parietal bone.
The Squamo-parietal, or squamous suture, is arched. It is formed by the squa-mous portion of the temporal bone overlapping the middle division of the lower border of the parietal.
The Masto-parietal is a short suture, deeply dentated, formed by the posterior inferior angle of the parietal, and the superior border of the mastoid portion of the temporal.
The sutures at the base of the skull are the basilar in the centre, and on each side, the petro-occipital, the masto-occipital, the peiro-sphenoidal, and the squamo-sphenoidal.
The Basilar Suture is formed by the junction of the basilar si'rface of the occipital bone with the posterior surface of the body of the sphenoid. At an early period of life a thin plate of cartilage exists between these bones, but in the adult they become inseparably united. Between the outer extremity of the basilar suture, and the termination of the lambdoid, an irregular suture exists which is subdivided into two portions. The inner portion, formed by the union of the petrous part of the temporal, with the occipital bone, is termed the petro-occipital. The outer portion, formed by the junction of the mastoid part of the temporal with the occipital, is called the masto-occipital. Between the bones forming the petro-occipital suture, a thin plate of cartilage exists; in the masto-occipital is occasionally found the opening of the mastoid foramen. Between the outer extremity of the basilar suture and the spheno-parietal, an irregular suture may be seen formed by the union of the sphenoid with the temporal bone. The inner and smaller portion of this suture is termed the petro-sphenoidal; it is formed between the petrous portion of the temporal, and the great wing of the sphenoid; the outer portion, of greater length, and arched, is formed between the squamous portion of the temporal and the great wing of the sphenoid, it is called the squamo-sphenoidal.
The cranial bones are connected with those of the face, and the facial with each other, by numerous sutures, which, though distinctly marked, have received no special names. The only remaining suture deserving especial consideration is the transverse. This extends across the upper part of the face, and is formed by the junction of the frontal with the facial bones; it extends from the external angular process of one side, to the same point on the opposite side, and connects the frontal with the malar, the sphenoid, the ethmoid, the lachrymal, the superior maxillary, and the nasal bones on each side.
THE SKULL
The Skull, formed by the union of the several cranial and facial bones already described, when considered as a whole, is divisible into five regions; a superior region or vertex, an inferior region or base, two lateral regions, and an anterior region, the face.
The Superior Region, or vertex, presents two surfaces, and external and an internal. The External Surface is bounded in front by the nasal eminences, and superciliary ridges; behind, by the occipital protuberance and superior curved lines of the occipital bone, laterally, by an imaginary line extending from the outer end of the superior curved line, along the temporal ridge, to the external angular process of the frontal. This surface includes the vertical portion of the frontal, the greater part of the parietal, and the superior third of the occipital bone; it is smooth, convex, of an elongated oval form, crossed transversely by the coronal suture, and from before backwards by the sagittal, which terminates behind in the lambdoid. From before backwards may be seen the frontal eminences and remains of the suture connecting the two lateral halves of the frontal bone; on each side of the sagittal suture is the parietal foramen and parietal eminence, and still more posteriorly the smooth convex surface of the occipital bone.
The Internal Surface of the vertex is concave, presents eminences and depressions for the convolutions of the brain, and numerous furrows for the lodgment of branches of the meningeal arteries. Along the middle line of this surface is a longitudinal groove, narrow in front, where it terminates in the frontal crest, broader behind; it lodges the superior longitudinal sinus, and its margins afford attachment to the falx cerebri. On either side of it are several depressions for the Pacchionian bodies, and at its back part, the internal openings of the parietal foramina. This surface is also crossed in front by the coronal suture; from before backwards, by the sagittal; behind, by the lambdoid.
BASE OF THE SKULL
The Inferior Region, or base of the skull presents two surfaces, an internal or cerebral, and an external or basilar.
The Internal, or Cerebral Surface, is divisible into three parts, or fossae, called the anterior, middle, and posterior fossae of the cranium.
Base of Skull
The Anterior Fossa is formed by the orbital plate of the frontal, the cribriform plate of the ethmoid, the ethmoidal process and lesser wing of the sphenoid. It is the most elevated of the three fossae, convex on each side where it corresponds to the roof of the orbits, concave in the median line in the situation of the cribriform plate of the ethmoid. It is traversed by three sutures, the ethmoido-frontal, ethmo-sphenoidal, and fronto-sphenoidal, and lodges the anterior lobes of the cerebrum. It presents in the median line from before backwards, the commencement of the groove for the superior longitudinal sinus, and crest for th.e attachment of the falx cerebri; the foramen coecum, this aperture is formed by the frontal and crista galli of the ethmoid, and if pervious, transmits a small vein from the nose to the superior longitudinal sinus. Behind the foramen coecum is the crista galli, the posterior margin of which affords attachment to the falx cerebri. On either side of the crista galli is the olfactory groove, which supports the bulb of the olfactory nerves, perforated by the three sets of orifices which give passage to its filaments; and in front by a slit-like opening, which transmits the nasal branch of the ophthalmic nerve. On each side are the internal openings of the anterior and posterior ethmoidal foramina, the former, situated about the middle of its outer margin, transmitting the nasal nerve, which runs in a groove along its surface, to the slit - like opening above mentioned; whilst the latter, the posterior ethmoidal foramen, opens at the back part of this margin under cover of a projecting lamina of the sphenoid, it transmits the posterior ethmoidal artery and vein to the posterior ethmoidal cells. Further back in the middle line is the ethmoidal spine, bounded behind by an elevated ridge, separating a longitudinal groove on each side which support the olfactory nerves. The anterior fossa presents laterally eminences and depressions for the convolutions of the brain, and grooves for the lodgment of the anterior meningeal arteries.
The Middle Fossa, somewhat deeper than the preceding, is narrow in the middle, and becomes wider as it expands laterally. It is bounded in front by the posterior margin of the lesser wing of the sphenoid, the anterior clinoid process, and the anterior margin of the optic groove; behind, by the petrous portion of the temporal, and basilar suture; externally, by the squamous portion of the temporal, and anterior inferior angle of the parietal bone, and is divided into two lateral parts by the sella Turcica. It is traversed by four sutures, the squamous, spheno-parietal, spheno-temporal, and petro-sphenoidal.
In the middle line, from before backwards, is the optic groove, which supports the optic commissure, terminating on each side in the optic foramen, for the passage of the optic nerve and ophthalmic artery, behind is seen the olivary process, and laterally the anterior clinoid processes, which afford attachment to the folds of the dura mater, which form the cavernous sinus. In the centre of the middle fossa is the sella Turcica, a deep depression, which lodges the pituitary gland, bounded in front by a small eminence on either side, the middle clinoid process, and behind by a broad square plate of bone, surmounted at each superior angle by a tubercle, the posterior clinoid process; beneath the latter process is a groove, for the lodgment of the sixth nerve. On each side of the sella Turcica is the cavernous groove; it is broad, shallow, and curved somewhat like the italic letter f; it commences behind at the foramen lacerum medium, and terminates on the inner side of the anterior clinoid process. This groove lodges the cavernous sinus, the internal carotid artery, and the orbital nerves. The sides of the middle fossa are of considerable depth; they present eminences and depressions for the middle lobes of the brain, and grooves for lodging the branches of the middle meningeal artery; these commence on the outer side of the foramen spinosum, and consist of two large branches, an anterior and a posterior; the former passing upwards and forwards to the anterior inferior angle of the parietal bone, the latter passing upwards and backwards. The following foramina may also be seen from before backwards. Most anteriorly is the foramen lacerum anterius, or sphenoidal fissure, formed above by the lesser wing of the sphenoid; below, by the greater wing; internally, by the body of the sphenoid; and completed externally by the orbital plate of the frontal bone. It transmits the third, fourth, the three branches of the ophthalmic division of the fifth, the sixth nerve, and the ophthalmic vein. Behind the inner extremity of the sphenoidal fissure is the foramen rotundum, for the passage of the second division of the fifth or superior maxillary nerve; still more posteriorly is seen a small orifice, the foramen Vesalii; this opening is situated between the foramen rotundum and ovale, a little internal to both; it varies in size in different individuals, and transmits a small vein. It opens below in the pterygoid fossa, just at the outer side of the scaphoid depression. Posteriorly and externally is the foramen ovale, which transmits the third division of •the fifth or inferior maxillary nerve, the small meningeal artery, and the small petrosal nerve. On the outer side of the foramen ovale is the foramen spinosum, for the passage of the middle meningeal artery; and on the inner side of the foramen ovale, the foramen lacerum medium. This aperture in the recent state is filled up with cartilage. On the anterior surface of the petrous portion of the temporal bone is seen from without inwards, the eminence caused by the projection of the superior semicircular canal, the groove leading to the hiatus Fallopii, for the transmission of the petrosal branch of the Vidian nerve; beneath it, the smaller groove, for the passage of the smaller petrosal nerve; and near the apex of the bone, the depression for the semilunar ganglion, and the orifice of the carotid canal, for the passage of the internal carotid artery and carotid plexus of nerves.
The Posterior Fossa, deeply concave, is the largest of the three, and situated on a lower level than either of the preceding. It is formed by the occipital, the petrous and mastoid portions of the temporal, and the posterior inferior angle of the parietal bones; is crossed by three sutures, the petro-occipital, masto-occipital, and masto-parietal; and lodges the cerebellum, pons varolii, and medulla oblon-gata. It is separated from the middle fossa in the median line by the basilar suture, and on each side by the superior border of the petrous portion of the temporal bone. This serves for the attachment of the tentorium cerebelli, is grooved externally for the superior petrosal sinus, and at its inner extremity presents a notch, upon which rests the fifth nerve. Its circumference is bounded posteriorly by the groove for the lateral sinus. In the centre of this fossa is the foramen magnum, bounded on either side by a rough tubercle, which gives attachment to the odontoid ligaments; and a little above these are seen the internal openings of the anterior condyloid foramina. In front of the foramen magnum is the basilar process, grooved for the support of the medulla oblongata and pons varolii, and articulating on each side with the petrous portion of the temporal bone, forming the petro-occipital suture, the anterior half of which is grooved for the inferior petrosal sinus, the posterior half being encroached upon by the foramen lacerum posterius, or jugular foramen. This foramen is partially subdivided into two parts; the posterior and larger division transmits the internal jugular vein, the anterior the eighth pair of nerves. Above the jugular foramen is the internal auditory foramen, for the auditory and facial nerves and auditory artery; behind and external to this is the slit-like opening leading into the aquaeductus vestibuli; whilst between these two latter, and near the superior border of the petrous portion, is a small triangular depression, which lodges a process of the dura mater, and occasionally transmits a small vein into the substance of the bone. Behind the foramen magnum are the inferior occipital fossae, which lodge the lateral lobes of the cerebellum, separated from one another by the internal occipital crest, which serves for the attachment of the falx cerebelli, and lodges the occipital sinuses. These fossae are surmounted, above, by the deep transverse grooves for the lodgment of the lateral sinuses, that on the right side being usually larger than the left. These channels, in their passage outwards, groove the occipital bone, the posterior inferior angle of the parietal, the mastoid portion of the temporal, and the occipital just behind the jugular foramen, at the back part of which they terminate. Where this sinus grooves the mastoid part of the temporal bone, the orifice of the mastoid foramen may be seen; and just previous to its termination it has opening into it the posterior condyloid foramen.
Base of Skull, External Surface
The External Surface of the base of the Skull is extremely irregular. It is bounded in front by the incisor teeth in the upper jaws; behind, by the superior curved lines of the occipital bone; and laterally, by the lower border of the malar bone, the zygomatic arch, and an imaginary line, extending from the zygoma to the mastoid process and extremity of the superior curved line of the occiput. It is formed by the palate processes of the two superior maxillary and palate bones, the vomer, the pterygoid, under surface of the great wing, spinous process and part of the body of the sphenoid, the under surface of the squamous, mastoid, and petrous portions of the temporal, and occipital bones. The anterior part of the base of the skull is raised above the level of the rest of this surface (when the skull is turned over for the purpose of examination), surrounded by the alveolar process, which is thicker behind than in front, and excavated by sixteen depressions for lodging the teeth of the upper jaw; they vary in depth and size according to the teeth they contain. Immediately behind the incisor teeth is the anterior palatine fossa or canal. At the bottom of this fossa may usually be seen four apertures, two placed laterally, which open above, one in the floor of each nostril, and transmit the anterior palatine vessels, and two in the median line of the intermaxillary suture, one in front of the other, the most anterior one transmitting the left, and the posterior one (the larger) the right naso-palatine nerve. These two latter canals are sometimes wanting, or they may join to form a single one, or one of them may open into one of the lateral canals above referred to. The palatine vault is concave, uneven, perforated by numerous nutritious foramina, marked by depressions for the palatal glands, and crossed by a crucial suture, which indicates the point of junction of the four bones of which it is composed. One or two small foramina, seen in the alveolar margin behindthe incisor teeth, occasionally seen in the adult, almost constant in young subjects, are called the incisive foramina; they transmit nerves and vessels to the incisor teeth. At each posterior angle is the posterior palatine foramen, for the transmission of the posterior palatine vessels and anterior palatine nerve, and running forwards and inwards from it a groove, which lodges the same vessels and nerve. Behind the posterior palatine foramen is the tuberosity of the palate bone, perforated by one or more accessory posterior palatine canals, and marked by the commencement of a ridge, which runs transversely inwards, and serves for the attachment of the tendinous expansion of the tensor palati muscle. Projecting backwards from the centre of the posterior border of the hard palate is the posterior nasal spine, for the attachment of the Azygos uvulae. Behind and above the hard palate is the posterior aperture of the nares, divided into two parts by the vomer, bounded above by the body of the sphenoid, below by the horizontal plate of the palate bone, and laterally by the pterygoid processes of the sphenoid. Each aperture measures about an inch in the vertical, and half an inch in the transverse direction. At the base of the vomer may be seen the expanded alas of this bone, receiving between them the rostrum of the sphenoid. Near the lateral margins of the vomer, at the root of the pterygoid process, are the pterygo-palatine canals. The pterygoid process, which bounds the posterior nares on each side, presents near its base the pterygoid or Vidian canal, for the Vidian nerve and artery. Each process consists of two plates, which bifurcate at the extremity to receive the tuberosity of the palate bone, and are separated behind l>y the pterygoid fossa, which lodges the Internal pterygoid muscle. The internal plate is long and narrow, presenting on the outer side of its base the scaphoid fossa, for the origin of the Tensor palati muscle, and at its extremity the hamular process, around which the tendon of this muscle turns. The external pterygoid plate is broad, forms the inner boundary of the zygomatic fossa, and affords attachment to the External pterygoid muscle.
Behind the nasal fossa in the middle line is the basilar surface of the occipital bone, presenting in its centre the pharyngeal spine for the attachment of the Superior constrictor muscle of the pharynx, with depressions on each side for the insertion of the Rectus anticus major and minor. At the base of the external pterygoid plate is the foramen ovale; behind this, the foramen spinosum, and the prominent spinous process of the sphenoid, which gives attachment to the internal lateral ligament of the lower jaw and the Laxator tympani muscle. External to the spinous process is the glenoid fossa, divided into two parts by the Glaserian fissure, the anterior portion being concave, smooth, bounded in front by the eminentia articularis, and serving for the articulation of the condyle of the lower jaw; the posterior portion rough, bounded behind by the vaginal process, and serving for the reception of part of the parotid gland. Emerging from between the laminae of the vaginal process is the styloid process; and at the base of this process is the stylo-mastoid foramen, for the exit of the facial nerve, and entrance of the stylo-mastoid artery. External to the stylo-mastoid foramen is the auricular fissure for the auricular branch of the pneumogastric, bounded behind by the mastoid process. Upon the inner side of this process is a deep groove, the digastric fossa; and a little more internally, the occipital groove, for the occipital artery. At the base of the internal pterygoid plate is a large and somewhat triangular aperture, the foramen lacerum medium, bounded in front by the great wing of the sphenoid, behind by the apex of the petrous portion of the temporal bone, and internally by the body of the sphenoid and basilar process of the occipital bone; it presents in front the posterior orifice of the Vidian canal, behind the aperture of the carotid canal. This opening is filled up in the recent subject by a fibro-cartilaginous substance; across its upper or cerebral aspect passes the internal carotid artery and Vidian nerve. External to this aperture, the petro-sphenoidal suture is observed, at the outer termination of which is seen the orifice of the canal for the Eustachian tube, and that for the Tensor tympani muscle. Behind this suture is seen the under surface of the petrous portion of the temporal hone, presenting, from within outwards, the quadrilateral rough surface, part of which affords attachment to the Levator palati and Tensor tympani muscles; behind this surface are the orifices of the carotid canal and the aquseductus cochleae, the former transmitting the internal carotid artery and the ascending branches of the superior cervical ganglion of the sympathetic, the latter serving for the passage of a small artery and vein to the cochlea. Behind the carotid canal is a very large irregular aperture, the jugular fossa, formed in front by the petrous portion of the temporal, and behind by the occipital; it is generally larger on the right than on the left side, and is perforated at the bottom by an irregular aperture; it is divided into two parts by a ridge of bone, which projects usually from the temporal; the anterior, or smaller portion, transmitting the three divisions of the eighth pair of nerves; the posterior, transmitting the internal jugular vein and the two ascending menin-geal vessels, from the occipital and ascending pharyngeal arteries. On the ridge of bone dividing the carotid canal from the jugular fossa, is the small foramen for the transmission of the tympanic nerve; and on the outer wall of the jugular foramen, near the root of the styloid process, is the small aperture for the transmission of Arnold 's nerve. Behind the basilar surface of the occipital bone is the foramen magnum, bounded on each side by the condyles, rough internally for the attachment of the alar ligaments, and presenting externally a rough surface, the jugular process, which serves for the attachment of the Rectus lateralis. On either side of each condyle anteriorly is the anterior condyloid fossa, perforated by the anterior condyloid foramen, for the passage of the lingual nerve. Behind each condyie are the posterior condyloid fossae, perforated on one or both sides by the posterior condyloid foramina, for the transmission of a vein to the lateral sinus. Behind the foramen magnum is the external occipital crest, terminating above at the external occipital tuberosity, whilst on each side are seen the superior and inferior curved lines; these, as well as the surfaces of the bone between them, being rough for the attachment of numerous muscles.
LATERAL REGIONS OF THE SKULL
The Lateral Regions of the Skull are somewhat of a triangular form, their base being formed by a line extending from the external angular process of the frontal bone along the temporal ridge backwards to the outer extremity of the superior curved line of the occiput; and the sides being formed by two lines, the one drawn downwards -and backwards from the external angular process of the frontal bone to the angle of the lower jaw, the other from the angle of the jaw upwards and backwards to the extremity of the superior curved line. This region is divisible into three portions, temporal, mastoid, and zygomatic.
THE TEMPORAL FOSSA
The Temporal Portion, or fossa, is bounded above and behind by the temporal ridge, which extends from the external angular process of the frontal upwards and backwards across the frontal and parietal bones, curving downwards behind to terminate at the root of the zygomatic process. In front, it is bounded by the frontal, malar, and great wing of the sphenoid: externally, by the zygomatic arch, formed conjointly by the malar and temporal bones; below, it is separated from the zygomatic fossa by the pterygoid ridge, seen on the under surface of the great wing of the sphenoid. This fossa is formed by five bones, part of the frontal, great wing of the sphenoid, parietal, squamous portion of the temporal, and malar bones, and is traversed by five sutures, the transverse facial, coronal, spheno-parietal, squamo-parietal, and squamo-sphenoidal. It is deeply concave in front, convex behind, traversed by numerous grooves for lodging the branches of the deep temporal arteries, and filled by the temporal muscle.
The Mastoid Portion is bounded in front by the anterior horizontal root of the zygoma; above, by a line which corresponds with the posterior root of the zygoma and the masto-parietal suture; behind and inferiorly, by the masto-occipital suture. It is formed by the mastoid and part of the squamous portion of the temporal bone; its surface is convex and rough for the attachment of muscles, and presents, from behind forwards, the mastoid foramen, below the mastoid process. In front of the mastoid process is the external auditory meatus, surrounded by the auditory process. Anterior to the meatus is the Glenoid fossa, bounded in front by the tubercle of the zygoma, behind by the auditory process, and above by the middle root of the zygoma, which terminates at the Glaserian fissure.
THE ZYGOMATIC FOSSAE
The Zygomatic fossae, are two irregular-shaped cavities, situated one on each side of the head, below, and on the inner side of the zygoma; bounded in front by the tuberosity of the superior maxillary bone and the ridge which descends from its malar process; behind, by the posterior border of the pterygoid process; above, by the pterygoid ridge on the under surface of the great wing of the sphenoid and squamous portion of the temporal; below, by the alveolar border of the superior maxilla; internally, by the external pterygoid plate; and externally, by the zygomatic arch and ramus of the jaw. It contains the lower part of the Temporal, the External, and Internal pterygoid muscles, the internal maxillary artery, the inferior maxillary nerve, and their branches. At its upper and inner part may be observed two fissures, the spheno-maxillary and pterygo-maxillary.
The Spheno-maxillary fissure, horizontal in direction, opens into the outer and back part of the orbit. It is formed above by the lower border of the orbital surface of the great wing of the sphenoid; below, by the posterior rounded border of the superior maxilla and a small part of the palate bone; externally, by a small part of the malar bone; internally, it joins at right angles with the pterygo-maxillary fissure. This fissure opens a communication from the orbit into three fossae, the temporal, zygomatic, and spheno-maxillary; it transmits the superior maxillary nerve, infra-orbital artery, and ascending branches from Meckel's ganglion.
The Pterygo-maxillary fissure is vertical, and descends at right angles from the inner extremity of the preceding; it is a triangular interval, formed by the divergence of the superior maxillary bone from the- pterygoid process of the sphenoid. It serves to conneftt the spheno-maxillary fossa with the zygomatic, and transmits branches of the internal maxillary artery.
THE SPHENO-MAXILLARY FOSSA
The Spheno-maxillary fossa is a small triangular space situated at the angle of junction of the spheno-maxillary and pterygo-maxillary fissures, and placed beneath the apex of the orbit. It is formed above by a small part of the under surface of the body of the sphenoid; in front, by the superior maxillary bone; behind, by the pterygoid process of the sphenoid; internally by the vertical plate of the palate; externally, it communicates with the spheno-maxillary fissure. This fossa has three fissures terminating in it, the sphenoidal, spheno-maxillary, and pterygo-maxillary; it communicates with three fossae, the orbital, nasal, and zygomatic, and with the cavity of the cranium, and has opening into it five foramina. Of these there are three on the posterior wall, the foramen rotundum above, the Vidian below and internal, and still more inferior and internal, the pterygo-palatine. On the inner wall is the spheno-palatine foramen by which it communicates with the nasal fossa, and below, the superior orifice of the posterior palatine canal, besides occasionally the orifices of two or three accessory posterior palatine canals.
ANTERIOR REGION OF THE SKULL
The Anterior Region of the Skull, which forms the face, is of an oval form, presents an irregular surface, and is excavated for the reception of the two principal organs of sense, the eye and the nose. It is bounded above by the nasal eminences and margins of the orbit; below, by the prominence of the chin; on each side, by the malar bone, and anterior margin of the ramus of the jaw. In the median line are seen from above downwards, the nasal eminences, which indicate the situation of the frontal sinuses; diverging outwards from them, the superciliary ridges which support the eyebrows. Beneath the nasal eminences is the arch of the nose, formed by the nasal bones, and the nasal process of the superior maxillary. The nasal arch is convex from side to side, concave from above downwards, presenting in the median line the inter-nasal suture, formed between the nasal bones, laterally the naso-maxillary suture, formed between the nasal and the nasal process of the superior maxillary bones, both these sutures terminating above in that part of the transverse suture which connects the nasal bones and nasal processes of the superior maxillary with the frontal. Below the nose is seen the heart-shaped opening of the anterior nares, the narrow end upwards, and broad below; it presents laterally the thin sharp margins which serve for the attachmentof the lateral cartilages of the nose, and in the middle line below, a prominent process, the anterior nasal spine, bounded by two deep notches. Below this is the intermaxillary suture, and on each side of it the incisive fossa. Beneath this fossa is the alveolar process of the upper and lower jaw, containing the incisive teeth, and at the lower part of the median line, the symphysis of the chin, the mental eminence, and the incisive fossa of the lower jaw.
Proceeding from above downwards, on each side are the supra orbital ridges, terminating externally in the external angular process at its junction with the malar, and internally in the internal angular process; towards the inner third of this ridge is the supra orbital notch or foramen, for the passage of the supra orbital vessels and nerve, and at its inner side a slight depression for the attachment of the cartilaginous pulley of the superior oblique muscle. Beneath the supra-orbital ridges are the openings of the orbits, bounded externally by the orbital ridge of the malar bone; below, by the orbital ridge formed by the malar, superior maxillary, and lachrymal bones; internally, by the nasal process of the superior maxillary, and the internal angular process of the frontal bone. On the outer side of the orbit, is the quadrilateral anterior surface of the malar bone, perforated by one or two small malar foramina. Below the inferior margin of the orbit, is the infra-orbital foramen, the termination of the infra-orbital canal, and beneath this, the canine fossa, which gives attachment to the Levator anguli oris; bounded below by the alveolar processes, containing the teeth of the upper and lower jaw. Beneath the alveolar arch of the lower jaw is the mental foramen for the passage of the mental nerve and artery, the external oblique line, and at the lower border of the bone, at the point of junction of the body with the rainus, a shallow groove for the passage of the facial artery.
THE ORBITS
The Orbits are two quadrilateral hollow cones, situated at the upper and anterior part of the face, their bases being directed forwards and outwards, and their apices backwards and inwards. Each orbit is formed of seven bones, the frontal, sphenoid, ethmoid, superior maxillary, malar, lachrymal and palate; but three of these, the frontal, ethmoid and sphenoid, enter into the formation of both orbits, so that the two cavities are formed of eleven bones only. Each cavity presents for examination, a roof, a floor, an inner and an outer wall, a circumference or base, and an apex. The Roof is concave, directed downwards and forwards, and formed in front by the orbital plate of the frontal; behind, by the lesser wing of the sphenoid. This surface presents internally the depression for the fibro-cartilaginous pulley of the superior oblique muscle; externally, the depression for the lachrymal gland, and posteriorly, the suture connecting the frontal and lesser wing of the sphenoid.
The Floor is nearly flat, and of less extent than the roof; it is formed chiefly by the orbital process of the superior maxillary; in front, to a small extent, by the orbital process of the malar, and behind, by the orbital surface of the palate. This surface presents at its anterior and internal part, just external to the lachrymal canal, a depression for the attachment of the tendon of origin of the inferior oblique muscle; externally, the suture between the malar and superior maxillary bones; near its middle, the infra-orbital groove; and posteriorly, the suture between the maxillary and palate bones.
The Inner Wall is flattened, and formed from before backwards by the nasal process of the superior maxillary, the lachrymal, os planum of the ethmoid, ind a small part of the body of the sphenoid. This surface presents the lachrymal groove, and crest of the lachrymal bone, and the sutures connecting the ethmoid, in front, with the lachrymal, behind, with the sphenoid.
The Outer Wall is formed in front by the orbital process of the malar bone; behind, by the orbital plate of the sphenoid. On it are seen the orifices of one or two malar canals, and the suture connecting the sphenoid and malar bones.
Angles. The superior external angle is formed by the junction of the upper and outer walls; it presents from before backwards, the sutures connecting the frontal with the malar in front, and with the orbital plate of the sphenoid behind; quite posteriorly is the foramen lacerum anterius, or sphenoidal fissure, which transmits the third, fourth, ophthalmic division of the fifth, and sixth nerves, and the ophthalmic vein. The superior internal angle is formed by the junction of the upper and inner wall, and presents the suture connecting the frontal with the lachrymal in front, and with the ethmoid behind. This suture is perforated by two foramina, the anterior and posterior ethmoidal, the former transmitting the anterior ethmoidal artery and nasal nerve, the latter the posterior ethmoidal artery and vein. The inferior external angle, formed by the junction of the outer wall and floor, presents the spheno-maxillary fissure, which transmits the infra-orbital vessels and nerve, and the ascending branches from the spheno-palatiue ganglion. The inferior internal angle is formed by the union of the lachrymal and os planum of the ethmoid, with the superior maxillary and palate bones. The circumference, or base, of the orbit, quadrilateral in form, is bounded above by the supra-orbital arch; below, by the anterior border of the orbital plate of the malar, superior maxillary, and lachrymal bones; externally, by the external angular process of the frontal and malar bone; internally, by the internal angular process of the frontal and nasal process of the superior maxillary. The circumference is marked by three sutures, the fronto-maxillary internally, the fronto-malar externally, and the malo-maxillary below; it contributes to the formation of the lachrymal groove, and presents above, the supra-orbital notch (or foramen), for the passage of the supra-orbital artery, veins, and nerve. The apex, situated at the back of the orbit, corresponds to the optic foramen, a short circular canal, which transmits the optic nerve and ophthalmic artery. It will thus be seen that there are nine openings communicating with each orbit, viz., the optic, foramen lacerum anterius, spheno-maxillary fissure, supra-orbital foramen, infra-orbital canal, anterior and posterior ethmoidal foramina, malar foramina, and lachrymal canal.
THE NASAL FOSSAE
The Naial Fossa are two large irregular cavities, situated in the middle line of the face, separated from each other by a thin vertical septum, and extending from the base of the cranium to the roof of the mouth. They communicate by two large apertures, the anterior nares, with the front of the face, and with the pharynx behind by the two posterior nares. These fossae are much narrower above than below, and in the middle than at the anterior or posterior openings: their depth, which is considerable, is much greater in the middle than at either extremity. Each nasal fossa communicates with four sinuses, the frontal in front, the sphe-noidal behind, and the maxillary and ethmoidal on either side. Each fossa also communicates with four cavities: with the orbit by the lachrymal canal, with the mouth by the anterior palatine canal, with the cranium by the olfactory foramina, and with the spheno-maxillary fossa by the spheno-palatine foramen; and they occasionally communicate with each other by an aperture in the septum. The bones entering into their formation are fourteen in number: three of the cranium, the frontal, sphenoid, and ethmoid, and all the bones of the face excepting the malar and lower jaw. Each cavity has four walls, a roof, a floor, an inner, and an outer wall.
The upper wall, or roof, is long, narrow, and concave from before backwards; it is formed in front by the nasal bones and nasal spine of the frontal, which are directed downwards and forwards; in the middle, by the cribriform lamella of the ethmoid, which is horizontal; and behind, by the under surface of the body of the sphenoid, and sphenoidal turbinated bones, which are directed downwards and backwards. This surface presents, from before backwards, the internal aspect of the nasal bones; on their outer side, the suture formed between the nasal, with the nasal process of the superior maxillary; on their inner side, the elevated crest which receives the nasal spine of the frontal and the perpendicular plate of the ethmoid, and articulates with its fellow of the opposite side; whilst the surface of the bones is perforated by a few small vascular apertures, and presents the longitudinal groove for the nasal nerve: further back is the transverse suture, connecting the frontal with the nasal in front, and the ethmoid behind, the olfactory foramina on the under surface of the cribriform plate, and the suture between it and the sphenoid behind: quite posteriorly are seen the sphenoidal turbinated bones, the orifice of the sphenoidal sinuses, and the articulation of the alaj of the vomer with the under surface of the body of the sphenoid.
Nasal Fossae
The floor is flattened from before backwards, concave from side to side, and wider in the middle than at either extremity. It is formed in front by the palate process of the superior maxillary; behind, by the palate process of the palate bone. This surface presents, from before backwards, the anterior nasal spine; behind this, the upper orifice of the anterior palatine canal; internally, the ele vated crest which articulates with the vomer; and behind, the suture between the palate and superior maxillary bones, and the posterior nasal spineThe inner wall, or septum, is a thin vertical septum, which separates the nasal fossae from one another; it is occasionally perforated, so that they communicate, and is frequently deflected considerably to one side. It is formed, in front, by the crest of the nasal bones and nasal spine of the frontal; in the middle, by the perpendicular lamella of the ethmoid; behind, by the vomer and rostrum of the sphenoid; below, by the crest of the superior maxillary and palate bones. It presents, in front, a large triangular notch, which receives the triangular cartilage of the nose; above, the lower orifices of the olfactory canals; and behind, the guttural edge of the vomer. Its surface is marked by numerous vascular and nervous canals, and traversed by sutures connecting the bones of which it is formed.
The outer wall is formed, in front, by the nasal process of the superior maxillary and lachrymal bones; in the middle, by the ethmoid and inner surface of the superior maxillary and inferior turbinated bones; behind, by the vertical plate of the palate bone. This surface presents three irregular longitudinal passages, or meatuses, formed between three horizontal plates of bone that spring from it; they are termed the superior, middle, and inferior meatuses of the nose. The superior meatus, the smallest of the three, is situated at the upper and back part of each nasal fossa, occupying the posterior third of the outer wall. It is situated between the superior and middle turbinated bones, and has opening into it two foramina, the spheno-palatine, at the back part of its outer wall, the posterior ethnioidal cells, at the front part of the upper wall. The opening of the sphenoidal sinuses is usually at the upper and back part of the nasal fossae, immediately behind the superior turbinated bone. The middle meatus, situated between the middle and inferior turbinated bones, occupies the posterior two-thirds of the outer wall of each nasal fossa. It presents two apertures. In front is the orifice of the infundibulum, by which the middle meatus communicates with the anterior ethmoidal cells, and through these with the frontal sinuses. At the centre of the outer wall is the orifice of the antrum, which varies somewhat as to its exact position in different skulls. The inferior meatus, the largest of the three, is the space between the inferior turbinated bone and the floor of the nasal fossa. It extends along the entire length of the outer wall of the nose, is broader in front than behind, and presents anteriorly the lower orifice of the lachrymal canal.
Inner Wall of Nasal Fossae
OS HYOIDES
The Hyoid bone is named from its resemblance to the Greek Upsilon; it is also called the lingual bone, from supporting the tongue, and giving attachment to its numerous muscles. It is a bony arch, shaped like a horse-shoe, and consisting of five segments, a central portion or body, two greater cornua, and two lesser cornua.
Os Hyoides
The Body forms the central part of the bone, is of a quadrilateral form, its anterior surface convex, directed forwards and upwards, and divided into two parts by a vertical ridge, which descends along the median line, and is crossed at right angles by a horizontal ridge, so that this surface is divided into four muscular depressions. At the point of meeting of these two lines is a prominent elevation, the tubercle. The portion above the horizontal ridge is directed upwards, and is sometimes described as the superior border. The anterior surface gives attachment to the Genio-hyoid in the greater part of its extent; above, to the Genio-hyo-glossus; below, to the Mylo-hyoid, Stylo-hyoid, and aponeurosis of the Digastric; and between these to part of the Hyo-glossus. The posterior surface is smooth, concave, directed backwards and downwards, and separated from the epiglottis by the thyro-hyoid membrane, and by a quantity of loose areolar tissue. The superior border is rounded, and gives attachment to the thyro-hyold membrane, and part of the Genlo-hyo-glossi muscles. The inferior border gives attachment in front to the Sterno-hyoid, behind to part of the Thyro-hyoid, and to the Omo-hyoid at its junction with the great cornu. The lateral surfaces are small, oval, convex facets, covered with cartilage for articulation with the greater cornua.
The Greater Cornua project backwards from the lateral surfaces of the body, they are flattened from above downwards, diminish in size from before backwards, and terminate posteriorly in a tubercle for the attachment of the thyro-hyoid ligament. Their outer surface gives attachment to the Hyo-glossus; their upper border, to the Middle constrictor of the pharynx; their lower border, to part of the Thyro-hyoid muscle.
The Lesser Cornua are two small conical shaped eminences, attached by their bases to the angles of junction between the body and greater cornua, and giving attachment by their apices to the stylo-hyoid ligaments. In youth the cornua are connected to the body by cartilaginous surfaces and held together by ligaments; in middle life, the body and greater cornua usually become joined; and in old age all the segments are united together, forming a single bone.
Development. By five centres; one for the body and one for each cornu. Ossification commences in the body and greater cornua towards the end of foetal life, those for the cornua first appearing. Ossification of the lesser cornua commences some months after birth.
Attachment of Muscles. Sterno-hyoid, Thyro-hyoid, Omo-hyoid, aponeurosis of the Digastricus, Stylo-hyoid, Mylo-hyoid, Genio-hyoid, Genio-hyo-glossus, Hyo-glossus, Middle constrictor of the pharynx, and occasionally a few fibres of the Lingualis. It also gives attachment to the thyro-hyoidean membrane, and the stylo-hyoid, thyro-hyoid, and hyo-epiglottic ligaments. PREVIOUS PAGE
