THE HAND
The Hand is subdivided into three segments, the Carpus or wrist, the Metacarpus or palm, and the Phalanges or fingers.
CARPUS
The bones of the Carpus, eight in number, are arranged in two horizontal rows. Those of the upper row, enumerated from the radial to the ulnar side, are the scaphoid, semi-lunar, cuneiform, and pisiform; those of the lower row, enumerated in the same order, are the trapezium, trapezoid, magnum, and unciform.
COMMON CHARACTERS OF THE CARPAL BONES
Each bone (excepting the pisiform) presents six surfaces. Of these, the anterior or palmar, and the posterior or dorsal, are rough, for ligamentous attachment, the dorsal surface being generally the broadest of the two. The superior and inferior are articular, the superior generally convex, the inferior concave; and the internal and external are also articular when in contact with contiguous bones, otherwise rough and tubercular. Their structure in all is similar, consisting within of a loose cancellous tissue enclosed in a thin layer of compact tissue. Each bone is also developed from a single centre of ossification.
BONES OF THE UPPER ROW
The Scaphoid is the largest bone of the first row. It has received its name from its fancied resemblance to a boat, being broad at one end, and narrowed like a prow at the opposite. It is situated at the superior and external part of the carpus, its direction being from above downwards, outwards, and forwards. Its superior surface is convex, smooth, of triangular shape, and articulates with the lower end of the radius. Its inferior surface, directed downwards, outwards, and backwards, is smooth, convex, also triangular, and divided by a slight ridge into two parts, the external of which articulates with the trapezium, the inner with the trapezoid. Its posterior or dorsal surface presents a narrow, rough groove, which runs the entire breadth of the bone, and serves for the attachment of ligaments. The anterior or palmar surface is concave above, and elevated at its lower and outer part into a prominent rounded tubercle, which projects forwards from the front of the carpus, and gives attachment to the anterior annular ligament of the wrist. The external surface is rough and narrow, and gives attachment to the external lateral ligament of the wrist. The internal surface presents two articular facets: of these, the superior or smaller one is flattened, of semi-lunar form, and articulates with the semi-lunar; the inferior or larger is concave, forming, with the semi-lunar bone, a concavity for the head of the os magnum.
To ascertain to which hand this bone belongs, hold the convex radial articular surface upwards, and the dorsal surface backwards; the prominent tubercle will be directed to the side to which the bone belongs.
Articulations. With five bones; the radius above, trapezium and trapezoid below, os magnum and semi-lunar internally.
The Semi-lunar bone may be distinguished by its deep concavity and crescentic outline. It is situated in the centre of the upper range of the carpus, between the scaphoid and cuneiform. Its superior surface, convex, smooth, and quadrilateral in form, articulates with the radius. Its inferior surface is deeply concave, and of greater extent from before backwards, than transversely; it articulates with the head of the os magnum, and by a long narrow facet (separated by a ridge from the general surface) with the unciform bone. Its anterior or palmar and posterior or dorsal surfaces are rough, for the attachment of ligaments, the former being the broader, and of somewhat rounded form. The external surface presents a narrow, flattened, semi-lunar facet, for articulation with the scaphoid. The internal surface is marked by a smooth, quadrilateral facet, for articulation with the cuneiform.
To ascertain to which hand this bone belongs, hold it with the dorsal surface upwards, and the convex articular surface backwards; the quadrilateral articular facet will then point to the side to which the bone belongs.
Articulations. With five bones: the radius above, os magnum and unciform below, scaphoid and cuneiform on either side.
The Cuneiform (V Os Pyramidal), may be distinguished by its pyramidal shape, and from having an oval-shaped, isolated facet, for articulation with the pisiform bone. It is situated at the upper and inner side of the carpus. The superior surface presents an internal, rough, non-articular portion ; and an external or articular portion, which is convex, smooth, and separated from the lower end of the ulna by the inter-articular fibre-cartilage of the wrist. The inferior surface, directed outwards, is concave, sinuously curved, and smooth, for articulation with the unciform. Its posterior or dorsal surface is rough, for the attachment of ligaments. Its anterior or palmar surface presents, at its inner side, an oval-shaped facet, for articulation with the pisiform; and is rough externally, for ligamentous attachment. Its external surface, the base of the pyramid, is marked by a flat, quadrilateral, smooth facefc, for articulation with the semi-lunar. The internal surface, the summit of the pyramid, is pointed and roughened, for the attachment of the internal lateral ligament of the wrist.
To ascertain to which hand this bone belongs, hold it so that the base is directed backwards, and the articular facet for the pisiform bone upwards; the concave articular facet will point to the side to which the bone belongs.
Articulations. With three bones: the semi-lunar externally, the pisiform in front, the unciform below, and with the triangular inter-articular fibro-cartilage which separates it from the lower end of the ulna.
The Pisiform bone may be known by its small size, and from its presenting a single articular facet. It is situated at the anterior and inner side of the carpus, is nearly circular in form, and presents on its posterior surface a smooth, oval facet, for articulation with the cuneiform bone. This facet approaches the superior, but not the inferior, border of the bone. Its anterior or palmar surface is rounded and rough, and gives attachment to the anterior annular ligament. The outer and inner surfaces are also rough, the former being convex, the other usually concave.
To ascertain to which hand it belongs, hold the bone with its posterior or articular facet downwards, and the non-articular portion of the same surface backwards; the inner concave surface will then point to the side to which the bone belongs.
Articulations. With one bone, the cuneiform.
Attachment of Muscles. To two: the Flexor carpi ulnaris, and Abductor minimi digit!; and to the anterior annular ligament.
Bones of the Left Hand
