OSSEOUS SYSTEM OF MAMMALIA. 



65 



ever, these portions become ossified, or consolidated, into one mass, but 

 which permanently retains the marks of its previous separation. In 

 man it is broad at its upper part, and becomes narrower as it proceeds ; 

 but in the lower Mammalia it is much narrower above, and does not 

 assume a form so decidedly triangular. The os sacrum unites with the 

 iliac, or haunch bones, to form the pelvis (or basin-like cavity, to the sides 

 of which, externally, the thigh-bones are articulated), and is continued by 

 the additional vertebrae, called the coccygal, or caudal, which have been 

 previously alluded to. In quadrupedal Mammalia the os sacrum, no 

 longer required to enter into part of a widely expanded pelvis, loses that 

 breadth and solidity, by which it is so characterized in the human subject. 

 Even in the Chimpanzee and Orang its lateral diameter is very much 

 diminished (figs. 66 and 67) in comparison with that of the human 

 subject (figs. 64 and 65) ; but, among the lower Mammalia, it appears 

 merely as two or three of the last lumbar vertebrae consolidated together, 

 and continued (especially in animals furnished with a tail organized for 

 any particular purpose, as the Beaver or Kangaroo,) by the caudal 

 vertebrae, amply developed for some distance. 



65 



Figs. 64, 65. Anterior and posterior view of the human pelvis. 66. Anterior view of the pelvis of the Chimpanwe. 

 67. Anterior view of the pelvis of the Orang.-o, os sacrum; *, the coccygal extremity, composed of caudal or coccygal 

 vertebra, varying in number in different Mammalia ; c , c, iliac bones ; d, pubic bones ; e, e, ischiatic bones ; /, /, acetabu- 

 lum, or socket, for the reception of the head of the thigh bone. (The same letters refer to the same part in all the above 

 figures.) 



In the human subject the coccyx consists of four caudal or coccygal 

 vertebrae, which, however, often unite into one undivided portion. In most 

 Mammalia, their number is far greater : they consist, with the exception 

 of the first few, of long bones, dilated at each extremity by the rudiments 



