OSTEOLOGY OF BIMANA. 



575 



the important share taken by both muscles in maintaining the 

 erect position. 



With the outer surface 

 of the ilium turned to the 

 observer, as in fig. 397, is 

 seen the same surface of 

 both ischium and pubis, 

 together with the aceta- 

 bulum; but, in the Gorilla, 

 the twist of the innomina- 

 tum is such as to present 

 only the outer margin of 

 the ischium, with a side 

 view of the acetabulum ; 

 and, in the Chimpanzee, 

 the o-reater twist brin2:s 

 the iniier surface of the 

 pubis into view and almost 

 excludes the acetabulum. 



The sacro-iliac surface 

 is divided into a ' syndes- 

 motic,' fig. 398, i, 7, and 

 a ' synchondrosal,' ib. n, 2, part : the latter is more especially termed 

 the ' articular,' and some- 

 times, from its shaj^e, the 

 ' auricular ' part ; it is 

 united by ' fibro-cartilage ' 

 to the first and second, 

 and a small part of the 

 third, sacral vertebrae. The 

 concavity, 4, is the ' inter- 

 nal iliac fossa.' The ridore, 

 5, transmits, like a but- 

 tress, the weight sustained 

 by the articular surface, 2, 

 to the back wall of the 

 acetabulum : the ridge, 6, 

 thence continued to the 

 spine of the pubis, /, is 

 termed 'ilio-pectineal.' 



The human pelvis, formed 

 by the sacrum, coccyx, and 



OSSa innominata, offers mtemal view or the os iunumiuatu.u. 



External view of the innominate bone. 



398 



