Vertehroid Homologies of the Cranium in Vertebralia. 53 
of the cranium, placed on the summit of the kaidon^ where 
the first and second cervical vertebree have a different rela- 
tion to one another from what is seen in the lower vertebrae : 
in order to give the extended motion enjoyed by the human 
cranium equivalent to the universal joint, the body of the 
axis, with its narrow lamellar tubercle and very prominent 
spine, has a strong odontoid process developed on the upper 
surface of the centrum, which intrudes, and in a manner re- 
places a large part of the body of the atlas, here reduced to 
a mere bony ring having a meso-spine on its ventral surface, 
while the axis is retained by a strong ligament behind it, 
completing the floor of the neural tunnel. The posterior ring 
of the atlas has the lamellar tubercles or transverse processes 
much produced, but the neural spines very small, greatly 
contrasting the axis in all particulars. 
The axo-atloid relation is carried out in the basicranium, 
where each centrum has a double perineural arch in the 
following ascending order : — 
BlVERTEBR/E. MeTA VERTEBR/E. 
I. Basi-occipital. © | 2°^^^°^^-: , ^'■'^^^^ 
^ IS. SuD-occipital spine. 
( Aocoid. P. Hyp-otic and Mammilla. L. Epi- 
II. Basi-otic. 0 j otic. 8. Wormi-otic. 
Atloid. P. Pro-otic and Mastoid. L. Parietal 
( Atloid. Alas majores — Orbito-sphenoid. 
III. Basi-sphenoid. 0 \ Axoid. Olivare. P. Optic. L. Ant. clinoid. 
Alge lugrassii. 
C Atloid. P. Supra-orbital plate and Supercili- 
IV. Ethmo- frontal. 0 I ary ridge. L. Os frontis. 
(_ Axoid. Ethmoid and turbinals. 
V. Apocranial. 0 Nasal protuberance and Ossa nasi. 
The relation of these vertehroid skelotomes of the cranium 
to the encephalon and the cranial nerves is very important, 
and deserves more notice than can be given in this hasty 
communication to the Royal Physical Society. Had time 
permitted, the vertebral analogies could be shown by the 
intervertebral transmission over the pedicle. This part of 
the subject, with the evidence afforded by development in 
the foetus, will form the subject of a future communication. 
