9io 



SUB-KINGDOM VERTEBRATA. 



very generally meet those of the opposite side in a ventral sym- 

 physis ; and when, as is frequently the case, the three bones of 

 either side are anchylosed together, an innominate bone results (fig. 



1 1 2 8 bis). The ischium and pubis 

 of the same side may also unite 

 inferiorly so as to enclose the 

 obturator notch, F, which then 

 forms the obturator foramen (fig. 

 1 1 2 8 bis) ; while an obturator pro- 

 cess of the ischium may form 

 a smaller foramen below the 

 acetabulum, as in the pelvis of 

 Camptosaurus, figured in the 

 sequel (fig. 1052). As a rule, 

 there is no tendency to a reduc- 

 tion in the number of the pelvic 

 bones in the higher forms. It 

 may be mentioned, in conclu- 

 sion, that a median ossification 

 at the ventral symphysis of the 

 pubis and ischium found in cer- 

 tain Edentates has been named the pelvisternum, and regarded as 

 the abdominal representative of the sternum. This appears, how- 

 ever, to correspond with the median ossification found in the 

 Ungulates (fig. 1 1 2 8 bis), which is generally looked upon merely as 

 an epiphysis. The pectoral and pelvic girdles of Fishes are noticed 

 in the next chapter. 



Fig. 831.— Lateral aspect of the left half of 

 the pelvis of a young Crocodilian {Alligator). 

 II, Ilium ; P, Pubis ; Is, Ischium ; F, Obtura- 

 tor notch ; a, b, a, Acetabulum, with its va- 

 cuity ; t> * s Cartilaginous extensions of ilium. 



It may be well to observe here that genera being purely and simply 

 artificial divisions formed for the convenience of classification, it is quite 

 unnecessary that they should be of equivalent value in different groups 

 of animals. As examples of vertebrate groups in which generic terms 

 are used in a wide sense, we may cite the Reptilan order Sauropterygia 

 and the Mammalian family RhinocerotidcR ; while as instances where a 

 more restricted application is employed, we may mention the order 

 Chelonia, and the family Bovidce. The statement we not unfrequently 

 hear that such-and-such a form must represent a distinct genus implies 

 a total misconception of the import of generic terms. 



