13 
The cranial vertebree are three in number, and may be named, from 
before backward, the frontal, parietal and occipital vertebre. 
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 heemal 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 well 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 vertebre ; 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 vertebra. 
The occipital vertebra has for its centrum the basi-occipital, for its 
neuropomata the ali-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 corresponding 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. 
