CROCODILIA, 91 



given in PI. 3, fig. 8, and an under view of the same in fig. 9, showing the two hyp- 

 apophysial ridges extending from tlie articular facets for the hsemapophyses atone end 

 to the other end of the centrum. 



The segments of the endo-skelcton composing the skull are more modified than 

 those of the pelvis ; but just as the vertebral pattern is best preserved in the neural 

 arches of the pelvis, which are called collectively ' sacrum,' so, also, is it in the same 

 arches of the skull, which are called collectively ' cranium.' The elements of which these 

 cranial arches are composed preserve, moreover, their primitive or normal individuality 

 more completely than in any of the vertebrre of the trunk, except the atlas, and 

 consecpiently the archetypal character can be more completely demonstrated. 



In fossil Crocodilia, and many other reptiles, the bones of the head are very liable 

 from this cause to a greater extent of dislocation and separation than happens to the 

 skull of the warm-blooded animal, in which a greater proportion of those primitive 

 bones coalesce with age. It not unfrequently happens that detached bones of the 

 skull of a reptile are found fossil, and the usually much modified form of these vertebral 

 elements renders their determination difficult. In order to diminish this difiiculty, I 

 subjoin some figures of the individual bones from my work on the ' Archetype of the 

 Vertebrate Skeleton,' with such indication of their natural connexions, as is compatible 

 with a clear outline. A profile or side view of all the bones is offered in fig. 13, and 

 as those of the cranium are least familiar to the pateontologist in their detached state, 

 I have added a direct view of them nearly as they are arranged in the formation of the 

 successive neural arches of the skull. Such figures are the more necessary in the 

 present state of anatomy and palaeontology, since the illustrations of the osteology of 

 the crocodile which have hitherto been prefixed to the descriptions of the fossil remains 

 of the Reptilian class, as, e. g., in the great work of Cuvier, include only figures of the 

 bones in question as they are naturally combined together in the entire skull. 



If, after separating the atlas from the occiput, we proceed to detach the occipital 

 segment of the cranium from the next segment in Pi„. g. 



advance, we find the detached segment presenting the 

 form of the neural arch, and it is easily and naturally 

 divisible into the four bones figured in Cut 9. The dotted 

 circle crosses the mars-ins at which the bones were joined v 

 together, in order to encompass the hindmost segment 

 of the brain, called ' epencephalon,' whence this neural 

 arch of the occiput is termed ' epencephalic arch.' 



No. 1 is the base of the arch, and is the 'centrum' or Bonesoftliedisarticulatedepencephalic 



body of the whole occipital vertebra : it presents, like arch, viewed from behind (Crocodae). 

 those of the trunk, a convexity or ball at its posterior articular surface, but its anterior 

 one, like the hindmost centrum of the sacrum, unites with the next centrum in advance 

 by a flat rough ' sutural' or ' symphysial' surface. Like most of the centrums in the 



