90 



THE SKELETON OF THE HORSE 



middle; on its lower part are lateral rough depressions, surmounted by tuberosities, 

 to both of which ligaments are attached. 



The posterior or volar surface is smooth, flattened, and slopes obliquely down- 

 ward and forward. The borders which separate the anterior and posterior surfaces 

 are concave from above downward, rounded from before backward. 



Development. — The second phalanx ossifies like the first, but the proximal 

 end unites with the shaft two or three months earlier. 



/♦ Distal border 



Dorsal or wall surface 

 . Extensor process 



, '■ Articular surface 

 :.i--' Coronary border 

 V'-^" Dorsal groove 



Third Phalanx 



Third Sesamoid 



Second Phalanx ^ 



Depression for lateral ligament 



Angle or wing 



Articular surface of third sesamoid or 

 navicular bone 



Distal articular surface 

 Eminence for lateral ligament 



First Phalanx 



-^ — Dorsal surf ace 



Proximal articular surface 



' — Distal articular surface 



*»-- Eminence for lateral ligament 



Dorsal surface 



" Eminence for extensor tendons 



— Tuberosity 



— Proximal articular surface 



— Intermediate groove 

 Fig. 58. — Phalanges and Third Sesamoid of Horse, Dorsal Aspect. 



The Third Phalanx 



The third or ungual phalanx (Phalanx tertia)' is entirely inclosed by the hoof, 

 to which it conforms in a general way. It presents for examination three surfaces, 

 three borders, and two angles or wings. 



The articular surface (Facies articularis) faces upward and backward, and is 

 chiefly adapted to the distal surface of the second phalanx, but a narrow flattened 

 area along the posterior border articulates with the third sesamoid. The an- 



' This bone is also called the os pedis or coffin bone. 



