54 Proceedings of the Royal Physical Society. 



Without attempting 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 haemo-splanchnic axes, which consists of mere cellular 

 substance within a structureless sheath, forming a primitive 

 centre 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 Bivertebrahegms 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 

 by the anterior part of the basilar process {posterior clinoids), 



