Vertebroid Homologies of the Cranium in Vertebralia. 53 



of the cranium, placed on the summit of the frauhm, where 

 the first and second cervical vertebrae 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 : — 



BlVERTEBRJ2. M ETA VERTEBR J2. 



L Basi-occipital. ©{ ^. Condyloid i. Edge of Foramen magnun,. 

 r ( S. Sub-occipital spine. 



Axoid. P. Hyp-otic and Mammilla. L. Epi- 

 II. Basi-otic. otic. S. Wormi-otic. 



Atloid. P. Pro-otic and Mastoid. L. Parietal. 



(Atloid. Alae majores — Orbito-sphenoid. 



< Axoid. 



III. Basi-sphenoid. 0 ■< Axoid. Olivare. P. Optic. L. Ant. clinoid. 



(_ Alae Ingrassii. 



^Atloid. P. Supra-orbital plate and Supereili- 



IV. Ethmo-frontal.© < ary ridge. L. Os frontis. 



Axoid. Ethmoid and turbinals. 



V. Apocranial. ® Nasal protuberance and Ossa nasi. 



The relation of these vertebroid 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 Eoyal 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. 



