98 THE ARTISTIC ANATOMY OF ANIMALS 



it has not a homologue in the tarsus of other animals. Its 

 external surface is rough ; its superior border is furnished 

 with a small pointed process occupying a depression which 

 is provided for it by the tibia. It reaches lower down than 

 the latter, and forms in this way a sort of external malleolus, 

 which frames, on the outer aspect, the mortise in which the 

 astragalus is maintained. 



The tarsus, as a whole, has an elongated form ; it is formed 

 of five bones : the astragalus, calcaneum, cuboid and scaphoid, 

 which coalesce, to form a single bone, and two cuneiform 

 bones, which correspond to the second and third cuneiform 

 bones of the human foot. These cuneiforms are called, from 

 their size, commencing internally, by the names small and 

 great cuneiform. 



The calcaneum is long and narrow ; it is longer than that 

 of the horse ; it is on the anterior and external part that 

 the bone (coronoid tarsal bone) which represents the inferior 

 extremity of the fibula is situated. It forms the prominence 

 known as the point of the ham, a prominence which is no 

 other than the heel, which, in the unguligrades, is, as we 

 have already said, very far removed from the ground. 



The astragalus, which is elongated in the vertical direc- 

 tion, has three articular surfaces disposed in the form of 

 trochleas : a superior trochlea, which is in contact with the 

 skeleton of the leg, and which is present in all animals ; an in- 

 ferior, which replaces the articular head found on the anterior 

 aspect of the astragalus in man ; this articulates with the 

 portion of the scaphoido-cuboid that corresponds to the 

 scaphoid ; and, lastly, a posterior trochlea with which the 

 -calcaneum articulates. Of these three trochlese, the superior 

 ,is the most strongly marked. Between this latter and the 

 inferior is found, on the anterior surface of the astragalus, 

 a deep depression, which, during flexion of the foot on the 

 leg, receives a prominence which the inferior extremity of 

 the tibia presents in its median portion. 



We can easily recognise the trochleae which we have been 

 discussing, in the little bones which children use ' to play 

 at bones ' ; these bones are no other than the astragali of 

 '.sheep. 



