DIGIT. 



79 



towards its anterior surface, to articulate with a portion of the 

 OS magnum, while the external splint has but one carpal facet, 

 which gives support to the unciform bone. Below the articular 

 surface, externally, the heads are rough- 

 ened for the insertion of the tendon of 

 the flexor metacarpi intern us to the inner, 

 and that of the flexor metacarpi externus 

 to the outer. The head of each 

 of these bones presents two articular 

 facets, which correspond to those on the 

 sides of the head of the cannon bone. 

 The middle part or body tapers grad- 

 ually downwards from the head, and is 

 firmly attached to the large metacarpal 

 bone by its anterior surface. The apex 

 terminates in a small knob, which never, 

 except in disease, becomes attached to 

 the parent bone. These knobs are very 

 prominent in well-bred horses, and are 

 sometimes mistaken for splints, which 

 are exostoses between the large and small 

 metacarpal bones. 



The digit or finger is composed of 

 three bones placed one immediately below 

 the other, and having three supplemen- 

 tary or sesamoid bones placed behind. 

 The three principal bones are homologous 

 with the three phalanges of the human 

 finger, the os suffraginis representing the 

 first or proximal, the os coronae the 

 second or median, and the os pedis the 

 third or distal phalanx. 



The joint which the large metacarpal 

 bone forms with the os suffraginis and 

 its two sesamoids is the fetlock -joint, 

 that between the os suffraginis and the os corona? is the pastern 

 joint, and that between the os coronse and the os pedis, with its 

 sesamoid or navicular bone, is the coffin joint. 



D 



Fig. 19. 

 Posterior view of phalanges of 

 a Horse disarticulated. A, Os 

 suffraginis ; B, Os coronae ; C, Os 

 pedis ; D, Os naviculare, or third 

 sesamoid ; 1 1, Glenoid cavities, 

 joined by the groove, 2 ; 3, Eough 

 surface for V-shaped sesamoidean 

 ligament ; 4 4, Condyles articu- 

 lating with cavities, 5 5 ; 6 6, Con- 

 dyles of coronas articulating with 

 glenoid cavities of pedal bone, 

 7 7 ; 8 S, Pyramidal process ; 9 9, 

 Basilar processes ; 10 10, Retros- 

 sal processes ; 11 11, Articular 

 surfaces between navicular and 

 pedal bones ; 12, Surface, con- 

 tinuous with glenoid cavities, 7 7 ; 

 13, Posterior edge ; and 14 14, 

 Extremities for lateral ligaments 

 of navicular bone. 



