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FOSSIL REPTILIA OF THE 



In Crocodilia the pubis (fig. 13, p b), as in birds, is a simple style slightly expanded 

 distally where it articulates with a cartilaginous abdominal sternum, 1 but it joins not 

 there, directly, either its fellow or the ischium. It contributes no part to the acetabulum, 

 but is attached at its proximal end to an anteriorly produced part of the same end of the 

 ischium (ib. is). 



In Chelonia the pubis is remarkable for its breadth, due to its distal expansion ; 

 proximally it contributes to the acetabulum, articulating there with both ilium and 

 ischium, and at or near half way to the distal end, it sends forward a broad and termi- 

 nally thick pectineal process ; 2 it unites distally with its fellow, and in some species also, 

 as in Monotremes, with the ischium, dividing the obturator space. The average pro- 

 portions and common character of the pubis in Lacertilia are given in Cut, fig. 15, 

 Monitor; the - perforation d marks the closer resemblance to the Dinosaurian pubis 

 (fig. 12, P b). 



Notwithstanding the difference in the proportions of breadth and length, the pubis in 

 Iguanodon and Omosaurus, in its essential characters, is more like that in the Tortoise 

 than in any bird. But these proportions are among the most variable characters of the 

 bone, and we have not far to seek in the Lacertian order before finding, as in Uromastyx, 

 a pubis combining with the pectineal process (PI. XX, figs. 8 and 9, b), as slender a body 

 thence continued as in the Dinosauria. Only, in Omosaurus, the proximal end of the 

 bone seems not to contribute any share to the acetabular cavity ; and, if this should be 

 the case with other Dinosaurs, those extinct reptiles would combine, in their pelvis, as in 

 some other parts of their skeleton, characters now restricted respectively to the Croco- 

 dilian and Lacertian groups of the class. 



Thus, the ischium, in Omosaurus, has no other ' process ' save the stunted homologue 

 of the proximal extension supporting the pubis in Crocodilia. 



In Chelonia, as in Uromastyx, there is a distinct posterior process (marked c in figs 

 8 and 9, PI. XX) ; but in certain Lizards {Varanus niloticus, e. g.) 3 it is reduced to a mere 

 rudiment, and in the Chameleon it ceases to exist. Thus, the Omosaurus resembles the 

 Crocodilia and some Lacertilia in the simplicity of its ischium, and markedly departs 

 from the type of birds in respect to this bone. 



But it is alleged that the ilium gives evidence of the avian affinity of Dinosaurs which 

 we have now proved to be wanting in the rest of the pelvis. Among the " points of 

 difference between any existing Reptile and any existing Bird," the following is put by 

 Professor Huxley in the foreground. 



"1. In the Reptile the ilium is not prolonged in front of the acetabulum." " In the 

 bird the ilium is greatly prolonged in front of the acetabulum." 



1 ' Anat. of Vertebrates,' vol. i, p. 68, fig. 56, 5. 



2 'Anat. of Vertebrates,' vol. i, fig. 116, h. 



3 Cuvier, • Ossemens Fossiles,' torn, cit., pi. xvii, fig. 40, c. 



