CRANIUM PROPER, 49 
1. The cranium proper. An unsegmented cartilaginous 
tube whose cavity forms the anterior part of the 
neural canal and lodges the brain. The roof of the 
tube is imperfect, there being one large anterior 
fontanelle, and two smaller posterior fontanelles, 
which are closed by membrane only. In the cartilage 
ot developed cartilage bones, and around it membrane 
ones. 
To study the cranium satisfactorily, the membrane bones should 
# stripped from one of the skulls you have prepared as durected 
above. 
a. Cartilage bones of cranium proper. 
4, The exoccipitals: two irregular bony masses at the 
sides of the posterior end of the skull. They 
almost completely surround the foramen magnum 
or entrance to the cranial cavity ; and bear on 
their posterior surfaces the occipital condyles, 
two oval convex processes which articulate with 
the first vertebra or atlas. 
| Ai. The sphenethmoid or girdle-bone: a bony tube 
which encircles the anterior end of the cranial 
cavity, and extends forwards into the olfactory 
region: in front it is divided by a vertical partition 
into right and left cavities, in which lie the 
olfactory nerves. 
b. Membrane bones of cranium proper. © 
i. The fronto-parietals: two long flat bones on the top 
of the brain-case ; covering the fontanelles, and 
overlapping the hinder end of the sphenethmoid. 
ii. The parasphenoid : a |. shaped bone on the ventral 
surface of the cranium: its lateral processes 
underlying the auditory capsules. 
