304 THE SKELETON OF THE RABBIT. 



bones in this way, it must be borne in mind that, inasmuch as 

 they are primitively independent of the cartilaginous skeleton, 

 any attempt to group them according to the divisions of this 

 primary skeleton must be more or less arbitrary. 



1. The cranium proper, or brain-case, forms the posterior 

 part of the skull, and is situated almost completely 

 behind the orbits, or sockets for the eyeballs. The 

 anterior or facial part of the skull is not in a line 

 with the base of the cranium, but is deflected down- 

 wards through angle of about 60. 



The bones of the cranium proper are arranged 

 in a series of segments or rings, one in front of the 

 other : of these, the hindmost or occipital segment 

 is the most obvious, and is very easily detached from 

 the rest of the skull as a bony ring. 



Care must be taken not to confuse these segments 

 with vertebrae, with which they do not correspond. 



a. The occipital segment consists entirely of cartilage- 

 bones, which may fuse together inseparably. It 

 articulates with the first vertebra by means of the 

 occipital condyles. 



i. The basi-occipital is a flat median bone, forming 

 the floor of the hinder part of the cranial 

 cavity. It forms the ventral boundary of 

 the foramen magnum, and a small part of 

 each occipital condyle. 



ii. The ex-occipitals bound the foramen magnum 

 laterally, and form the greater part of the 

 condyles. Each is produced at its outer side 

 into a long downwardly directed par-occipital 

 process, which is closely applied to the pos- 

 terior surface of the tympanic bulla. 



iii. The supra-occipital is a large median bone, 

 which completes the occipital segment above. 

 The whole bone is markedly cancellous, and 

 its outer surface is raised into a prominent 



