ANATOMY OF VEUTEBRATES. 



127 



In fig. 90, the centrum i, neurapophyses 2, and neural spine 

 3, of the epencephalic arch, are seen from their inner or cranial 

 surfiice : -vvith the increasing bulk of the brain, the spine, 3, 

 begins to expand laterally, and take a greater share in roofing- 

 over the hinder part or epencephalon : the parapophysis, 4, is 

 excluded in this view. The gristly capsule of the ear-organ fills 

 up the otocrane formed by the bones, 2, 3, 5, and 6 ; and extends 

 outward and backward to enter the basal cavity of 4, the par- 



90 



Section of cranium. Turtle (Chelone mydas^ 



occipital : were ossification to extend into the acoustic capsule, 

 either from an independent centre, like 16, figs. 81, 83, 84, or 

 by continuous growth from any of the otocranial bones, the true 

 homologue of the ' petrosal ' or ' petrous portion of the temporal 

 bone ' of Anthropotomy would be established. In some Emydians 

 there is a small autogenous bony plate in the acoustic cartilage, 

 close to the foramen caroticum. 



The basisphenoid, 5, continues forward the series of cranial 

 centrums, expands beneath the cranial cavity, articulates on each 

 side with the alisphenoid, 6, and sends out from its under and 

 lateral surface a plate to articulate with the pterygoids, fig. 98 b, 24, 

 and, in the Emys, with the petrosal. The alisphenoid, 6, fig. 90, 

 protects the side of the mesencephalon (optic lolje), is widely 

 notched anteriorly by the emerging divisions (2ncl and 3rd) of the 

 trigeminal nerve, is perforated posteriorly by a filament of the 

 acoustic nerve, where it joins the cartilaginous petrosal ; it 

 articulates above with the mastoid, 8, and parietal, 7, and in 

 front with the orbitosphenoid, 11. The anterior semicircular 

 canal is partly lodged in the cavity of the otocraue contributed 



