PELVIC ARCH. 



95 



Reptiles usually extends forwards for some distance in the middle 

 line, a large space (foramen cordiforme) is present between it and 

 the ischium : in Lizards, Crocodiles, and Turtles, this space 

 is divided into two halves by a median fibre-cartilaginous band 

 (Fig. 79, Kn, Kn l , B}. In land and fresh -water Tortoises, in 

 place of this band, the median ends of the pubis and ischium 

 extend towards one another and meet in the mid-ventral line, and 

 thus the space (obturator foramen) between them becomes entirely 

 surrounded by bone. 



FIG. 80. PELVIS OF A YOUNG Alligator Indus. (A, ventral, and B, side view.) 



II, ilium ; Is, ischium ; P, pubis ; Sy, symphysis of ischium ; F, foramen cordiforme + 

 obturatum ; B, fibrous band between the symphyses pubis and ischii ; f, carti- 

 laginous apophysis of the ventral acetabular process of the ischium, which is 

 interposed between the process a of the ilium and the pubis ; b, foramen in 

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

 and ischium respectively, which here meet one another ; *, indication of a for- 

 ward growth of the ilium, such as is met with in Dinosaurians and Birds ; G, 

 acetabulum ; /, //, first and second sacral vertebrae ; M, fibrous membrane ex- 

 tending between the anterior margin of the pubis and the last pair of "abdominal 

 ribs " (SS). 



In Crocodiles we meet for the first time with a considerable 

 extension of the ilium (Fig. 80, B, 77), so that now a longer 

 posterior, and a shorter anterior process may be distinguished. In 



