140 THE VERTEBRATE SKELETON. 



the newt is really the axis, and that the atlas with the excep- 

 tion of the odontoid process has become fused with the skull. 

 The sacral vertebra or sacrum, differs from the vertebrae 

 immediately in front of it only in the fact that its transverse 

 processes are stouter and more obviously divided into dorsal 

 and ventral portions. 



THE CAUDAL VERTEBRAE. 



The caudal vertebrae are about twenty-four in number. 

 The anterior ones have hour-glass shaped centra, and short 

 backwardly-directed transverse processes. The middle and 

 posterior ones have rather shorter centra, and are without 

 transverse processes. The neural arches resemble those of the 

 trunk vertebrae, but each is drawn out into a rather high 

 cartilaginous neural spine abruptly truncated anteriorly. All 

 the caudal vertebrae except the first have also a haemal arch, 

 which is very similar to the neural arch, and is drawn out 

 into a haemal spine quite similar to the neural spine. Both 

 neural and haemal arches are ossified continuously with the 

 centra. 



B. THE SKULL. 



The skull of the newt is divisible into three principal 

 parts : 



(1) an axial part, the cranium proper, which encloses 

 the brain and to which 



(2) the capsules of the auditory and olfactory sense 

 organs are fused ; 



(3) the skeleton of the jaws and hyoid apparatus. 

 The skull is much flattened and expanded, though not so much 

 as in the frog. 



(1) THE CRANIUM PROPER. 



The cranium proper or brain case is an unsegmented 

 tube which remains partly cartilaginous, and is partly con- 

 verted into cartilage bone, partly sheathed by membrane bone. 

 The roof and floor of the cartilaginous cranium are, as is 



