THE SKELETON OF THE VERTEBRATE HEAD. 181 



In the bird, the occipital neural arch wants the ex-occipitals. 

 The temporal arch possesses no centrum, but the petrosals, 

 mastoids, and parietals are placed one over the other as two 

 pairs of neurapophyses and a divided meta-neurapophysis. 

 The post-sphenoidal centrum is surmounted by the post- 

 sphenoidal wings and the feebly-developed post-frontals as 

 two pairs of neurapophyses, while the meta-neurapophysis is 

 deficient. 



In the crocodiles, the occipital arch, as in the birds, has 

 lost the upper pair of neurapophyses. The temporal centrum 

 is not developed, but the two pairs of neurapophyses, and an 

 undivided meta-neurapophysis the petrosals (ali-sphenoids 

 of Owen), mastoids, and so-called parietal form a continuous 

 arch. The post-sphenoidal centrum is again found to carry 

 two pairs of neurapophyses, the great sphenoidal wings (orbito- 

 sphenoids of Owen), and the post-frontals. The meta- 

 neurapophysis is missing. 



In the chelonians, the occipital arch consists of one pair 

 of neurapophyses and a meta-neurapophysis surmounting a 

 centrum. The temporal centrum is not developed. The 

 inferior pair of neurapophyses, the so-called ex-occipitals, abut 

 externally against the mastoids, and are thus connected with 

 the largely-developed so-called "parietals." These "parietals" 

 not only form a large part of the cranial and temporal vaults, 

 but send down laminae to rest on the pterygoids, and thus 

 enter into the formation of the lateral walls of the cranial 

 cavity in front of the post-sphenoidal wings. Above the post- 

 sphenoidal centrum, the post-sphenoidal wings and the post- 

 frontals rise in connection with one another as two pairs of 

 neurapophyses, but the meta-neurapophysis is again wanting. 



In the ophidians, the occipital centrum is again surmounted 

 by one pair of neurapophyses and a meta-neurapophysis. The 

 temporal centrum has disappeared behind the basi-sphenoid ; 

 but the well-developed so-called " petrosals," the ali-sphenoids 



