78 THE ARTISTIC ANATOMY OF ANIMALS 



At the same time, if we examine the felidae which we have 

 taken as examples, when the first phalanges are in the state 

 of extension, the digits will be found to be separable, as we 

 have already indicated in connection with the metacarpo- 

 phalangeal articulations, with the result that the claws are 

 then able to lacerate a wider surface. 



The extension of the ungual phalanx, which determines 

 the retraction of the claw and stops its action, is the 

 mechanical result of an elastic, fibrous apparatus which is 

 attached to each of the third phalanges, and has its origin 

 of the second. 



THE POSTERIOR LIMBS* 



The posterior limbs are divided, as are the inferior limbs 

 of the human being, of which they are the homologues, into 

 four parts : pelvis, thigh, leg, and foot. 



The Pelvis 



The pelvis, which incompletely limits the abdominal 

 cavity, inferiorly in the vertical position of the body and 

 posteriorly in the normal attitude of quadrupeds, is formed 

 by the iliac bones and sacrum — the coccyx forming a pro- 

 longation of the latter. We have already described the two 

 latter (pp. lo and ii) in connection with the vertebral 

 column, of which they form the inferior or posterior por- 

 tion or segment, according to the attitude of the individual. 



The Iliac Bone. — The iliac or coxal bone, is a paired or non- 

 symmetrical bone, united below to its fellow of the opposite 

 side, while it is separated from it above by the sacrum. 



In all animals, as well as in man, the iliac bone, at the 

 beginning of life, consists of three parts, which afterwards 

 unite and fuse together and join at the middle of the bottom 

 of a deep cavity which is situated on the outer aspect of the 

 bone — the cotyloid cavity. 



Of those three portions when examined in the human iliac 

 bone, that above the cavity is the ilium ; that on the inside 

 is the pubis ; and the last, the lower one, is the ischium. In 



* Examine Figs. 21,33, 34, 38. 39- 49- 



