80 OSTEOLOGY. 



PROXIMAL PHALANX. 



(Fio. 19. A.) 



The first phalanx, 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 

 semilunar-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. 



(Fm. 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 



