82 TEE BONES. 



is composed of two lateral condyles separated by a median spine. The two 

 condyles would be exactly alike, if the antero-posterior diameter of the 

 external condyle was not less extensive than that of the opposite condyle. 

 Both are hoUowed on the sides by an excavation for the attachment of 

 ligamentous fasciculi. 



Structure and development. — The principal metacarpal is one of the 

 most compact bones in the body. It is developed from two centres of 

 ossification, one of which is for the inferior extremity. 



EuDiMBNTAET Mbtaoabpals. — The two rudimentary (small) metacarpal 

 (or splint) bones are elongated, and placed against the posterior face of the 

 principal bone, one without, the other within. Each is in the form of an 

 inverted pyramid, and exhibits a middle jiart and two extremities. 



Middle portion. — Prismatic and triangular, this offers: 1, Three faces, — an 

 external, smooth and rounded from one border to the other ; an internal, 

 plane, and equally smooth ; an anterior, covered with asperities to give 

 attachment to the interosseous ligament uniting the lateral metacarpal bone 

 to the median ; 2, Three salient borders which markedly separate the faces 

 from each other. 



Extremities. — The superior, the largest, is named the head, and shows : above, 

 a diarthrodial facet which corresponds to one or two bones of the inferior row 

 of the carpus ; in front, other two small facets continuous with the pre- 

 ceding, and in contact with similar facets on the jnedian metacarpal bone ; 

 on the other points of its periphery are rugosities for the attachment of 

 ligamentous and tendinous fibres. The inferior extremity only reaches to 

 about the lower fourth of the large metacarpal bone, and terminates in a 

 small enlargement or button, which is never consolidated with the latter. 



The two lateral metacarpals, although very much alike, may yet be 

 easily distinguished from each other. For instance, the internal bone is 

 always the thickest and often the longest ; besides, the superior articular 

 surface of its head results from the union of the two facets corresponding 

 to the two last carpal bones of the lower tier. 



Structure and development. — Of a somewhat compact texture, like all 

 the long bones, these have no medullary canal, and are developed from only 

 one ossific centre. Not unfrequently, however, the tubercle is formed from 

 a special centre. 



3. Bones of the Phalangeal Segion or Digit. 



Solipeds have only one digit, supported by the principal metacarpal bone, 

 and composed of three pieces placed end to end, one upon another. The 

 first comprises three bones : a principal, the first phalanx, and two com- 

 plementary ones, the sesamoids. The second is formed by the second 

 phalanx, and the last, which terminates the limb, is constituted by the 

 third phalanx and an accessory bone which has received the name of the 

 small sesamoid (navicular hone). 



First (proximal) ob Mbtaoaepal Phalanx. — The first phalanx (or 

 pastern hone), the smallest of all the long bones, is situated in an oblique 

 direction from above downwards, and behind to before, between the principal 

 metacarpal and the second phalanx. 



Body. — Depressed in front and behind, this bone exhibits : an anterior 

 face, round from one side to the other, and slightly roughened above and 

 below ; a posterior face, flat, covered with ligamentous imprints in the form 

 of "a triangle with the base reversed ; two lateral horders, thick, rounded, and 

 provided with some imprints. 



