54 Proceedings of the Royal Physical Society. 
Without attemptiDg to examine fully the course of de- 
velopment of the human cranium, a slight sketch is neces- 
sary to show the coincidence between the foetal and adult 
condition. 
Professor Huxley has assumed that there are three states 
or conditions of the human foetal cranium. 
I. The membranous or vesicular cranium, when the 
skelon is entirely membranous, consisting of investing tissue 
enclosing the centrochord (noto-chord) between the neural 
and hsemo-splanchnic axes, which consists of mere cellular 
substance within a structureless sheath, forming a primitive 
pentre around which the bodies of the vertebrae are so placed 
as to afford a floor or basement for the cephalo-myelon to 
rest upon, over which the neur-arcs raise an arched tunnel 
by the anchylosis of the neural spinous process of each meta- 
vertebral skelotome in adult condition. 
II. The chondro-cranium, shortly after foetal development 
has commenced, may be traced, at several points, around 
both the cephalic and spinal centrochord in the cartila- 
ginous square masses observable on each side, and which 
appear to be the tubercles of the neur-arcs, which are first 
ossified, and from whence ossification of the pedicle extends 
to the centrum vertebrae, and in the other direction completes 
the lamella, and ultimately terminates the spinous processes. 
In the basi-cranium a similar process may be observed around 
the foramen magnum and onward. 
III. The Osteo-cranium, commencing with the basicra- 
nial axis, in the . same order as when describing the chondro- 
skelon. 
(i.) The Occipital Bivertehrahegms to show points of ossi- 
fication before they appear in the vertebral kaulon. At 
birth the occipital bone consists of separate pieces : 1. Basi- 
lar ; 2. Condyloid ; 3. The cerebellar fossae, formed in mem- 
brane about the same time that the wormi-otic spine appears 
in two points. The different parts of the occipital bivertebra 
are not completely ossified before the sixth year. 
(ii.) The Basi-otic Bivertebra. — The centrum 5 is formed 
hy the anterior part of the basilar process {posterior clinoicis), 
