152 



COMPARATIVE ANATOMY 



becomes connected with an increasing number of vertebrae, and so 

 forms a firmer support to the body. 



Birds. The pelvis of Birds is chiefly characterised by the 

 relatively large development of the iliac region and by the position 

 of the delicate pubis, which in the course of development becomes 



FIG. 112. PELVIS OF A YOUNG Alligator lurittx. A, ventral, and B, 



lateral view. 



B, fibrous band between the pubis and symphysis ischii ; /<, foramen in the 

 acetabulum, bounded posteriorly by the two processes, and b, of the ilium 

 and ischium respectively ; F, ischiopubic foramen ; G, acetabulum ; 77, ilium ; 

 /S ischium ; M, fibrous membrane extending between the anterior margin of 

 the pubis and the last pair of "abdominal ribs" (.#/'); P, pubis ; Xy. 

 symphysis of ischium ; *, indication of a forward growth of the ilium, such 

 as is met with in Dinosaurians and Birds ; f, pars acetabularis, which is 

 interposed between the process a of the ilium and the pubis ; /, //, first and 

 second sacral vertebra?. 



directed backwards, parallel to the ischium and postacetabular 

 process of the ilium. The preacetabular portion of the ilium 

 extends forward for a considerable distance, and a number of 

 vertebrae belonging to other than the true s;icral region become- 

 secondarily connected with the ilium (cf. p. 60). The acetabulum 

 is perforated, and the pars acetabularis forms a pectineal pro- 

 cess which is retained in the adult in Apteryx (Fig. 113). The 



