486 



COMPARATIVE ANATOMY. 



Fig. 271. View of the left side of a Bird's pelvis. 

 The dotted portion represents that part of the three 

 pieces of the pelvis, which extends backwards by the 

 development of cartilage. The dotted line marks off 

 that portion of the ilium (bb) which grows forwards 

 without the addition of any cartilage. The letters as 

 in the preceding figures. 



of the acetabulum,, takes the same course ; its ends project farther back 

 than those of the ischium, and generally converge ; in Struthio they 



even form a symphy- 

 sis. There are various 

 kinds of connections 

 between the ilium and 

 ischium, and between 

 these and the pubis. 



The pelvis in the 

 Mammalia is very dif- 

 ferent. The primi- 

 tive connection 

 with the sacrum 

 is always in front 

 of the acetabulum. 

 The ilium, however, 

 is directed from be- 

 fore backwards, and 

 the hinder edge of the 

 Bird's ilium corresponds to the anterior edge of the Mammal's 

 ilium. Two different positions therefore for the ilium are derived 

 from the Amphibia. In the Amphibia it is directed laterally and 

 inferiorly away from its connection with the sacrum, in Keptilia 

 and Aves obliquely forwards, and in Mammalia obliquely back- 

 wards. The ventral portion of the pelvis encloses an obturator 



foramen, and is united ven- 

 trally with that of the other 

 side. 



The primitive pelvic carti- 

 lage gives rise to the ilium and 

 ischium ; the pubis is derived 

 from a separate rudiment, 

 which is united with the 

 ischio-iliac rudiment in the 

 acetabulum (Man). This leads 

 us to think that the pubis is 

 an independent piece of the 

 skeleton, which has retained 

 its independence in the Cro- 

 codilini. The ilium of the 

 Mammalia is connected with 

 a few vertebras. The ischium 

 also may be united with the 

 false sacral vertebras (Dasy- 

 pus, Bradypus). When the 

 two ventral pieces are united at the ischio-pubic symphysis, as they 

 are in the Marsupialia, many Rodents, Artiodactyla, and Peris- 

 sodactyla, the pelvis is elongated in form. In the Insectivora 

 and Carnivora the greater part of the symphysis is formed by 



Fig. 272. View of the left side of the pelvis 



of a Dog. il Ilium, is Ischium. j> Os 



pubis. vl Penultimate lumbar vertebra. 



vc Caudal vertebra. 



