THE FOOT
The Foot is the terminal part of the inferior extremity; it serves to support the body in the erect posture, and as an important instrument of locomotion. It consists of three divisions: the Tarsus , Metatarsus, and Phalanges.
THE TARSUS
The bones of the Tarsus are seven in number; viz., the calcaneum, or os calcis, astragalus, cuboid, scaphoid, internal, middle, and external, cuneiform bones. These bones may be conveniently arranged into two lateral rows. The outer row, remarkable for its great solidity and strength, forms the basis of support to the foot; it consists of two bones, the os calcis and cuboid. The inner row, which contributes chiefly to its elasticity, is formed by the astragalus, scaphoid, and three cuneiform bones.
THE CALCANEUM
The Calcaneum, or Os Calcis, is the largest bone of the tarsus. It is irregularly cuboidal in form, and situated at the lower and back part of the foot. It presents for examination six surfaces; superior, inferior, external, internal, anterior, and posterior.
The superior surface is formed behind, of the upper edge of that process of the os calcis which projects backwards to form the heel. This process varies in length in different individuals; it is convex from side to side, concave from before backwards, and corresponds above to a mass of adipose substance placed in front of the tendo Achillis. In the middle of this surface are two (sometimes three) articular facets, separated by a broad shallow groove, directed obliquely forwards and outwards, and rough for the attachment of the interosseous ligament connecting the astragalus and os calcis. Of these two articular surfaces, the external is the larger, and situated upon the body of the bone; it is of an oblong form, broader behind than in front, and convex from before backwards. The internal articular surface is supported on a projecting process of bone, called the lesser process of the calcaneum (sustentaculum tali); it is of an oblong form, concave longitudinally, and sometimes subdivided into two, which differ in size and shape. More anteriorly is seen the upper surface of the greater process, marked by a rough depression for the attachment of numerous ligaments, and the tendon of origin of the Extensor brevis digitorum muscle.
Calcaneum
The inferior surface is narrow, rough, uneven, broader behind than in front, and convex from side to side; it is bounded posteriorly by two tuberosities, separated by a rough depression: the external, small, prominent, and rounded, gives attachment to part of the Abductor minimi digiti; the internal, broader and larger, for the support of the heel, gives attachment, by its prominent inner margin, to the Abductor pollicis, and in front to the Flexor brevis digitorum muscles, and the depression between the tubercles to the Abductor minimi digiti, and plantar fascia. The rough surface in front of these tubercles gives attachment to the long plantar ligament; and to a prominent tubercle nearer the anterior part of the bone, as well as to the transverse groove in front, is attached the short plantar ligament.
The external surface is subcutaneous, and presents near its centre a tubercle, for the attachment of the middle fasciculus of the external lateral ligament. Behind the tubercle is a broad smooth surface, giving attachment, at its upper and anterior part, to the external astragalo-calcanean ligament; and in front a narrow surface marked by two oblique grooves, separated by an elevated ridge: the superior groove transmits the tendon of the Peroneus brevis; the inferior, the tendon of the Peroneus longus; the intervening ridge gives attachment to a prolongation from the external annular ligament.
The internal surface presents a deep concavity, directed obliquely downwards and forwards, for the transmission of the plantar vessels and nerves and Flexor tendons into the sole of the foot; it affords attachment to part of the Flexor accessorius muscle. This surface presents in front an eminence of bone, the lesser process, which projects horizontally inwards from the upper and front part of this surface. This process is concave above, and supports the anterior articular surface of the astragalus; below, it is convex, and grooved for the tendon of the Flexor longus pollicis. Its free margin is rough, for the attachment of ligaments.
The anterior surface, of a somewhat triangular form, is smooth, concavo-convex, and articulates with the cuboid. It is surmounted, on its outer side, by a rough prominence, which forms an important guide to the surgeon in the performance of Chopart's operation.
The posterior surface is rough, prominent, convex, and wider below than above. Its lower part is rough, for the attachment of the tendo Achillis; its upper part smooth, coated with cartilage, and corresponds to a bursa which separates this tendon from the bone.
Articulations. With two bones: the astragalus and cuboid.
Attachment of Muscles. Part of the Tibialis posticus, the tendo Achillis, Plan-taris, Abductor pollicis, Abductor minimi digiti, Flexor brevis digitorum, Flexor accessorius, and Extensor brevis digitorum.
THE CUBOID
The Cuboid bone is placed on the outer side of the foot, immediately in front of the os calcis. It is of a pyramidal shape, its base being directed upwards and inwards, its apex downwards and outwards. It may always be known from all the other tarsal bones, by the existence of a deep grove on its under surface, for the tendon of the Peroneus longus muscle. It presents for examination six surfaces; three articular, and three non-articular: the non-articular surfaces are the superior, inferior, and external.
The superior or dorsal surface, directed upwards and outwards, is rough, for the attachment of numerous ligaments. The inferior or plantar surface presents in front a deep groove, which runs obliquely from without, forwards and inwards; it lodges the tendon of the Peroneus longus, and is bounded behind by a prominent ridge, terminating externally in an eminence, the tuberosity of the cuboid, the surface of which presents a convex facet, for articulation with the sesamoid bone of the tendon contained in the groove. The ridge and surface of bone behind it are rough, for the attachment of the long and short plantar ligaments. The external surface, the smallest and narrowest of the three, presents a deep notch, formed by the commencement of the peroneal groove.
The articular surfaces are the posterior, anterior, and internal. The posterior is a smooth, triangular, concavo-convex surface, for articulation with the anterior surface of the os calcis. The anterior, of smaller size, but also irregularly triangular, is divided by a vertical ridge into two facets; the inner quadrilateral in form, to articulate with the fourth metatarsal bone; the outer larger and more triangular, for articulation with the fifth metatarsal. The internal surface is broad, rough, irregularly quadrilateral, presenting at its middle and upper part a small oval facet, for articulation with the external cuneiform bone; and behind this (occasionally) a smaller facet, for articulation with the scaphoid; it is rough in the rest of its extent, for the attachment of strong interosseous ligaments.
To ascertain to which foot it belongs, hold the bone so that its under surface, marked by the peroneal groove, looks downwards, and the large concavo-cpnvex articular surface backwards, towards the holder; the small non-articular surface marked by the commencement of the peroneal groove, will point to the side to which the bone belongs.
Articulations. With four bones: the os calcis, external cuneiform, and the fourth and fifth metatarsal bones, occasionally with the scaphoid.
Attachment of Muscles. Part of the Flexor brevis pollicis.
THE ASTRAGALUS
The Astragalus, next to the os calcis, is the largest of the tarsal bones. It is placed at the middle and upper part of the tarsus, supporting the tibia above, articulating with the malleoli on either side, resting below upon the os calcis, and joined in front to the scaphoid. This bone may easily be recognised by its large rounded head, the broad articular facet on its upper convex surface, and by the two articular facets separated by a deep groove on its under concave surface. It presents six surfaces for examination.
The superior surface presents, behind, a broad smooth trochlear surface, for articulation with the tibia; it is broader in front than behind, convex from before backwards, slightly concave from side to side. In front of the trochlea is the upper surface of the neck of the astragalus, rough for the attachment of ligaments. The inferior surface presents two articular facets separated by a deep groove. The groove runs obliquely forwards and outwards, becoming gradually broader and deeper in front: it corresponds with a similar groove upon the upper surface of the os calcis, and forms, when articulated with that bone, a canal, filled up in the recent state by the calcaneo-astragaloid interosseous ligament. Of the two articular facets, the posterior is the larger, of an oblong form, and deeply concave from side to side; the anterior, although nearly of equal length, is narrower, of an elongated oval form, convex from side to side, and often subdivided into two by an elevated ridge; the posterior articulates with the lesser process of the os calcis; the anterior, with the upper surface of the calcaneo-scaphoid ligament. The internal surface presents at its upper part a pear-shaped articular facet for the inner malleolus, continuous above with the trochlear surface; below the articular surface is a rough depression, for the attachment of the deep portion of the internal lateral ligament. The external surface presents a large triangular facet, concave from above downwards, for articulation with the external malleolus; it is con tinuoua above with the trochlear surface: in front is a deep rough margin, for the attachment of the anterior fasciculus of the external lateral ligament. The anterior surface, convex and rounded, forms the head of the astragalus; it is smooth, of an oval form, and directed obliquely inwards and downwards; it is continuous below with that part qf the anterior facet on the under surface which rests upon the calcaneo-scaphoid ligament. The head is surrounded by a constricted portion, the neck of the astragalus. The posterior surface is narrow, and traversed by a groove, which runs obliquely downwards and inwards, and transmits the tendon of the Flexor longus pollicis.
Astragalus
To ascertain to which foot it belongs, hold the bone with the broad articular surface upwards, and the rounded head forwards; the lateral triangular articular surface for the external malleolus will then point to the side to which the bone belongs.
Articulations, With four bones; tibia, fibula, os calcis, and scaphoid. NEXT PAGE
