CEREBRAL DEVELOPMENT, ETa 35 



CEREBRAL DEVELOPMENT OF THE EARLIER 

 YERTEBRATA. 



ITS APPAEENT PKINCIPLE. 



It is held by a class of naturalists, some of them of the high- 

 est standing, that the skulls of the vertebrata consist, like the 

 columns to which they are attached, of vertebral joints, com- 

 posed each, in the more typical forms of head, as they are in 

 the trunk, of five parts or elements, — the centrum or body, 

 the two spinous processes which enclose the spinal cord, and 

 the two ribs. These cranial vertebrae, foui in number, cor- 

 respond, it is said, to the four senses that have their seat in 

 the head. There is the nasal vertebra, the centrum of which 

 is the vomer, its spinal processes the nasal and ethmoid bones, 

 and its ribs the wpper jaws ; there is the ocular vertebra, the 

 centrum of which is the anterior portion of the sphenoid bone, 

 its spinal processes the frontals, and its ribs the under jaws ; 

 there it the lingual vertebra, the centrum of which is the pos- 

 terior sphenoid bone, its spinal processes the parietals, and 

 its ribs the hyoid and branchial bones, — portions of the ske- 

 leton largely developed in fishes j and, lastly, there is the au- 

 ditory vertebra, the centrum of which is the base of the oc- 

 cipital bone, and its spinal processes the occipital crest, and 



