S90 THE ANATOMY OF THE HORSE 



thirdly, the posterior is irregular, and presents on its surface four smooth 

 faces for articulation with the os calcis, which are separated by roughened 

 excavations. The external side is marked by ligamentous impressions ; the 

 internal, smoother than the external, presents behind and below a little 

 tubercle, which gives attachment to ligaments. 



The Os Calcis {the heel-hone). — This bone, forming the point of the hock, 

 presents two surfaces, two borders, and two extremities ; the external 

 8U rf ace is almost plain ; the internal is excavated as a groove ; the anterior 

 is slightly concave ; the posterior is straight and roughened ; on the superior 

 extremity is a thick tuberous termination, to which the hamstrings are 

 attached ; its inferior extremity is large and concave, and presents four 

 surfaces for articulation with the astragalus, os cuboides, and os scaphoides, 

 and a median rough interspace to which ligaments are attached. 



The Os Cuboides (kvIBos, a cube) is situated on the postero-external sides 

 of OS cuneiforme magnum and os scaphoides, between the inferior exti'emity 

 of the OS calcis and the head of the external small metatarsal bone and also 

 a portion of the superior extremity of the large metatarsal bone. It presents 

 six surfaces : a superior, which articulates with the os calcis : an inferior by 

 two facettes corresponds to similar ones situated on the large and external 

 small metatarsal bones just mentioned ; internally two arthrodial surfaces 

 occur, which face with similar surfaces on the os cuneiforme magnum and 

 OS scaphoides. The external, anterior, and posterior surfaces are roughened 

 for ligamentous attachment. 



The Os Scaphoides is in figure triangular ; the superior surface, smooth 

 and slightly concave, is entirely articulatory, with the exception of a little 

 groove, running to its middle from the outer side ; this surface corresponds 

 with the under surface of the astragalus. The inferior surface is similar to 

 the superior, except that it is slightly convex, and articulates with the 

 superior surface of the os cuneiforme magnum, and also on its internal 

 angle with the os cuneiforme parvum ; it offers also, on its postero-external 

 face, two small diarthrodial surfaces for articulation with the os cuboides ; 

 in the rest of its extent, it is roughened for ligamentous attachment. 



The Os Cuneiforme Magnum. — This bone, although smaller than the 

 scaphoid, at the same time greatly resembles it ; its superior surface articu- 

 lates with the inferior surface of that bone ; the inferior surface articulates 

 with the large metatarsal bone ; its external border is provided with two 

 arthrodial spots for articulation with corresponding ones on the os cuboides. 

 The internal border also offers a spot which articulates with a similar one on 

 the OS cuneiforme parvum ; its anterior border is roughened throughout. 



The Os Cuneiforme Parvum is situated on the internal side of the 

 tarsus This bone, smaller than all, is prolonged from before backwards, 

 flatten' d from one side to the other, and articulates with the os cuneiforme 

 magnum and with the large and internal small metatarsal bones, to which 

 it corresponds by four surfaces covered with cartil;i;,''>. 



