50 Proceedings of the Royal Physical Society. 
cranium of a deer or sheep in the Black Forest, which im- 
pressed them with the resemblance the cranium bore to a 
series of vertebrae more or less fused together, the theory of 
a unity of organisation, traceable throughout all the verte- 
brate and articulate classes, has been wrought out down- 
wards to the lowest Eozoa or Acrita. The main object of 
this communication is to point out the homologies which 
appear in the human cranium, as the first part of the subject, 
and especially, to determine the true homologies of the dif- 
ferent types from man to the lowest ichthyia or osseous fishes, 
and afterwards those analogous homologies of Scleroderms 
among the Annulozoa and ARTHR0Z0A(the Articulata. — Guv.) 
A few changes in the usual terms of the anatomical school 
will be required for the clear elucidation of this important 
subject. Shelon will be substituted for Endoskeleton, and 
the different segments will be styled Skelotomes. Instead 
of Exoskeleton or Scleroderm, ^c/ero^i will be used, and Sclero- 
tome for any segment seen in the Arthrozoa and Annulo 
zoa. Somatome will include a segment of both skelon and 
scleron^ together with the visceral or splanchnosJcelon, and 
the soft parts connected with them. These terms are 
slightly modified from those proposed by Professor Goodsir. 
The characteristic difference distinguishing the verte- 
BRALiA from all other members of the zoological scale is 
drawn from the existence of a central stem or haulon, usually 
styled the Spinal or Vertebral column. I restrict this term 
to the stem formed by the centra or bodies of the vertebrae 
continued through the basicranium, having sometimes a 
mesospine on its ventral aspect. On its dorsal aspect, the 
perineural tunnel protecting the myelon or spinal marrow, 
is formed by the coalescence of the neur-arcs on each side, 
firmly anchylosed to the individual skelotome of the kaulon, 
and extending backward to unite in the neural spine. 
These Neur-arcs are formed of three distinct parts, like 
all other laminse — 
1. The Pedicle fused into the vertebrae, and forming part 
of the aperture for transmitting the spinal nerves (trous des 
f'onjugaison) . 
2. The Lamella, generally the largest part, with the tubercle 
