114 SKELETON OF THE CROCODILE. 



would Otherwise have attended the elongation of the parts. 

 In the abdomen of the crocodile, the analogous subdivision 

 of the htemapophyses, there called abdominal ribs, allows 

 of a slight change of their length, in the expansion and 

 contraction of the walls of that cavity ; and since amphi- 

 bious reptiles, when on land, rest the whole weight of the 

 abdomen directly upon the ground, the necessity of the 

 modification for diminished liability to fracture further 

 appears. These analogies are important, as demonstrating 

 that the general homology of the elements of a natural 

 segment of the skeleton is not affected or obscured by 

 their subdivision for a special end. Now this purposive 

 modification of the h^mapophyses of the frontal vertebra, 

 is but a repetition of that which affects the same elements 

 in the abdominal vertebrae. 



Passing next to the haemal arch of the parietal verte- 

 bra, we are first struck by its small relative size. Its 

 restricted functions have not required it to grow in pro- 

 portion with the other arches, and it consequently retains 

 much of its embryonic dimensions. It consists of a 

 ligamentous " stylohyal," its pleurapophysis retaining the 

 same primitive histological condition which obstructs the 

 ordinary recognition of the same elements of the lumbar 

 haemal arches. A cartilaginous "epihyal," 39, intervenes 

 between this and the ossified " hsemapophysis," 40, which 

 bears the special name of ceratohyal. The haemal spine, 

 41, retains its cartilaginous state, like its honx)types, in 

 the abdomen ; there they get the special name of " abdo- 

 minal sternum," here of "basihyal." The basihyal has, 

 however, coalesced with the thyrohyals to form a broad 

 cartilaginous plate, the anterior border rising like a valve 

 to close the fauces, and the posterior angles extending 

 beyond and sustaining the thyroid and other parts of the 



