148 THE OSTEOLOGY OF THE REPTILES 



guishes the order from all others. The ilium is a strong bone firmly 

 united with the two pairs of stout sacral ribs, of which the posterior 

 is the larger. Below, the ilium articulates with the ischium only, to 

 form the acetabulum. In front of the acetabulum it is produced for- 

 ward to join ligamentously with an anterior process of the ischium, 

 enclosing between them a foramen of considerable size for the passage 

 of the obturator nerve. The ischium is a rather long bone, with a 

 thin, spatulate extremity which joins its mate in a median symphysis. 

 Its anterior process, which may be in part the real pubis, articulates 

 in front with the so-called pubis. This bone is slender, with a thin 

 and dilated anterior extremity which touches, or is closely approxi- 

 mated to, its mate only at its inner anterior corner, and is continuous 

 anteriorly, with a thin but strong plate of fascia joined to the para- 

 sternal ribs. With much reason it has long been urged that the an- 

 terior projection of the ischium represents the real pubis. ^ In early 

 life it is largely cartilaginous, but becomes fully ossified in the adult. 

 The so-called pubis is probably homologous with the prepubis of the 

 pterodactyls. It has no pubic foramen. 



The ilium of the Pterosauria, like that of all bipedal reptiles is pro- 

 duced anteriorly by the sides of the vertebrae, very much so in some 

 forms. The ischium and pubis are closely united into a more or less 

 broad plate, either with a thyroid foramen, as in Nydosaurus (Fig. 

 118 d) and Pteranodon, or with a small pubic foramen below the 

 acetabulum, as in Rhamphorhynchus, proving the normal structure 

 of the pelvis, though sutures have not been observed. The prepubes, 

 often called the real pubes, are either paired, as in Pterodactylus, or 

 united in a ventral band, as in Rhamphorhynchus, Pteranodon and 

 Nydosaurus (Fig. 118 d). They articulated with a tuberosity on the 

 front margin of the pubes and in all probability were continued in 

 front with a ligamentous sheath that enclosed the parasternal ribs. 

 The pubes and ischia meet in a symphysis below, though this has 

 been disputed for some. 



As remarkable as the pelvis of the crocodiles is that of the Dino- 



1 [The pubis of the Crocodilia gives attachment to a series of muscles which as a 

 whole are homologous with those that are attached to the true pubis in Sphenodon and 

 lizards (Gregory and Camp, Bulletin, Amer. Mus. Nat. Hist., 1918; Romer, ibid., 1923, 

 p. 606). If the true pubis of Crocodilia has become vestigial and the prepubis has 

 become the functional pubis, how did the prepubis capture the system of muscle 

 attachments of its predecessor? — Ed.] 



