FOSSIE VERTEBRATES — REPTILIA 631 
coracoids; coracoid small; ilium greatly prolonged in front of 
the acetabulum; the ischia joining on the median line below ; 
the pubis often with a strong posterior process, the post-pubic 
process. The form of the body and the head varies greatly in 
the different forms, being sometimes like that of the crocodiles 
and at other times like that of the birds, reptiles, or even the 
mammals. In the majority of the forms the hind limbs exceeded 
the anterior ones in size, and were used more commonly in 
- walking; in some of the later and more specialized forms the 
anterior pair of limbs had lost the ambulatory functions entirely 
and had become wholly prehensile in character. The feet were 
as variously developed as the other parts of the body; in some 
of the forms inclining towards the ungulate type and in others 
developing well-formed claws. The dentition varied from the 
carnivorous to the herbivorous, some forms having strong 
recurved tusks, with serrated anterior and posterior cutting 
edges, and others with the jaws filled with close-set grinding 
teeth. The external appearance presented as many differences 
as the skeleton; in size they varied from that of the great 
herbivorous forms much larger than an elephant to the little 
leaping carnivorous forms no larger than a jack-rabbit. The 
skin of some was smooth and of others thickly covered with 
bony dermal plates and excrescences. Some walked erect, using 
the strongly developed tail as an aid in supporting the body, 
while others were entirely quadrupedal. 
This great range of characters has led to a great number of 
different schemes of classification, in most of which the order 
Dinosauria has been recognized as a definite group, but it is con- 
stantly growing more difficult to keep the heterogenous assem- 
blage together. Through all the later attempts at classification 
there has been a recognition of three types of structure that 
have been regarded as of ordinal, subordinal, or family rank by 
the various authors. These three divisions were regarded by 
Baur as distinct groups having nothing to do with each other. 
"Baur, “Remarks on the Reptiles generally called Dinosaurs,” American Nat- 
uralist, May 1891. 
