80 



OSTEOLOGY. 



PROXIMAL PHALANX. 



(Fig. 19. A.) 



The first pbalanx, also called the os suffraginis, or large pastern 

 bone, passes obliquely downwards and forwards, and articulates 

 with the cannon bone above, and the median phalanx below. It 

 belongs to the class of long bones. 



The shaft, which is very short and slightly flattened from before 

 backwards, has an anterior surface convex and smooth, and a 

 posterior surface somewhat flattened, the latter presenting two 

 roughened ridges, in the form of a triangle, with its base upwards, 

 to which certain of the sesamoidean ligaments are attached. 



The proximal extremity, the larger of the two, presents a 

 semUunar-shaped articular surface, convex in front, and consisting 

 of two glenoid cavities for the condyles of the cannon bone, and 

 a deep connecting groove for the eminence between them ; 

 behind, on each side, is a roughened tuberosity for the attachment 

 of the crucial sesamoidean ligaments. The distal extremity, much 

 smaller than the proximal, presents two condyles connected by a 

 shallow groove, continuous with which, posteriorly, is a pit or 

 depression into which fits a prominent lip on the posterior part 

 of the median phalanx, and in the centre of the front there is a 

 slight eminence, to which a slip of the tendon of the extensor 

 pedis muscle is attached. On each side is a roughened depression 

 for the insertion of the lateral ligaments. 



GREAT SESAMOID BONES. 

 (Fig. 17. 11.) 



These bones, two in number, are placed side by side at the 

 postero-inferior part of the metacarpus and postero-superior part 

 of the OS suffraginis ; they are irregular or polyhedral in shape, 

 having smooth and concave anterior surfaces, the internal 

 bevelled edges of which- form a groove into which the ridge 

 at the distal extremity of the cannon bone is received, the 

 concave portions articulating with the condyles of that bone. 

 The posterior surfaces when in situ form a channel, which is 

 covered with fibro-cartilage, for the passage of the flexor tendons 

 of the digit. The superior extremity or apex of each bone is 

 roughened, as are also their lateral borders, which are grooved for 



