13 



The cranial vertebrae are three in number, and may be named, from 

 before backward, the frontal, parietal and occipital vertebrae. 



The supposed nasal vertebra has no existence, the bones presumed 

 to constitute it belonging to different categories. 



Each cranial vertebra is composed of a centrum, a neural and a 

 visceral arch ; the haemal arch is present only in the third or occipital 

 vertebra forming the so-called ' body of the atlas.' 



Between the neural arches of the cranial vertebra pass out diverti- 

 cula of the cerebral vesicles to the ' sense-capsules,' as vrell as the 

 ordinary cerebro-spinal sensero-motor nerves. The primary segments 

 of the brain are three in number. The special sense nerves, and those 

 of the cerebro-spinal system, correspond in number to the cranial 

 vertebral segments. The auditory capsule is intercalated between the 

 neuropomata of the second and third cranial vertebrae ; the optic 

 nerve issues between those of the first and second, while the corre- 

 sponding capsule is contained in the orbital cavity, protected by cer- 

 tain bones, pro-orbital, meso-orbital and meta-orbital, &c. ; the olfac- 

 tory capsules are situated in front of the first vertebra, and are thus 

 enabled to approximate mesially, separated only by the prolongation 

 of the body of the frontal vertebi'a. 



The occipital vertebra has for its centrum the basi-occipital, for its 

 neuropomata the ah-occipital, and for its neuracantha the supra- 

 occipital, which is sometimes divided into two. 



The basi-sphenoid is the centrum of the second or parietal vertebra ; 

 the neuropomata are termed ali-parietals, and the divisions of the 

 neuracantha parietals. 



The centrum of the frontal or most anterior vertebral segment is 

 formed by the pre-sphenoid, the neuropomata by the ali-frontal, and 

 the divided neuracantha by the frontals. 



The squamosal and mastoid bones may be regarded as belonging 

 to the same category as the ossa Wormiana, namely, the accessory 

 neuropomatous pieces. 



The post-petrosal bone in the Chelonia is erroneously regarded by 

 Professor Owen as the equivalent in the occipital vertebra of the an- 

 gioparal element of the body of the vertebra in fishes, or of the infe- 

 rior transverse process in the higher vertebrata, since both receive the 

 same name in his system. 



The mastoid is also regarded by Prof. Owen as the ' parapophysis ' 

 of the parietal vertebra. 



The visceral arch of the frontal vertebra is formed by the palato- 

 maxillary apparatus exclusive of the pro-maxilla, and by the malleus 

 leucus with the lower jaw in the mammalia, or by the os quadratum 

 and Meckel's cartilage with the appendages in birds and reptiles. 



The corresponcUng arch of the parietal is formed by the anterior 

 horn of the hyoid bone, and that of the occipital by the posterior 

 cornua and body of the same bone. 



