36 



THE CAT. 



[CHAP. in. 



Those projecting backwards have a smooth articular surface, which 

 looks mainly downwards, and are called posterior articular processes, 

 or postzyaapophyses. 



The anterior margin of each pedicle is somewhat concave, while 

 its posterior margin is generally more so. In this way, the vertebrae 

 being naturally juxtaposed, the adjoined concavities, or notches, of 

 two adjacent vertebrae, constitute a rounded opening termed an 

 inter vertebral foramen. These foramina communicate with the 

 neural canal, and enable nerves and vessels to pass thence outwards. 



The adjacent surfaces of the bodies of the vertebra? are nearly 

 flat, and are connected together by the intervention of a fibrous pad 

 the intervertebral substance which will be described later, 

 amongst the ligaments. 



The vertebrae are composed of cancellous bony tissue invested by 

 compact bone. The latter is most abundant on the arch and 

 processes. The body of each vertebra is almost entirely composed 

 of spongy substance traversed by canals for veins. 



Such is the general condition of most of the vertebra), but in 

 some of them certain of their parts and processes are wanting, while 

 in others there are additional parts and processes. 



5. The vertebra? are divisible into five different CATEGORIES. (See 

 Fig. 23, c, d, /, , and cd). 



First come those of the neck, which are termed cervical. They 

 are seven in number. 



Secondly, those of the back, which have the ribs attached to them 

 and are called dorsal. Of these there are thirteen. 



Thirdly, we find certain large vertebra? which do not bear ribs : 

 these are situate behind the dorsal vertebra? and are called lumbar. 

 There are seven of them. 



All the above are termed " true vertebrae," because they do not 

 become anchylosed together, but remain connected only by ligaments 

 and by the intervertebral substances. 



Behind these true vertebra? come three which are called " false," 

 and which sooner or later anchylose together to form a bony mass. 



This mass, termed the sacrum, comes immediately behind the 

 lumbar vertebra?, and part of it affords attachment on each side to 

 one of the haunch, or hip, bones. The sacral vertebrae thus anchy- 

 lose together to constitute the sacrum. The rest of the vertebra? are 

 called caudal, and form a series of some twenty bones which decrease, 

 gradually, backwards as regards their complexity of structure, but 

 increase in length to about the tenth, and then again become 

 successively shorter, as well as simpler, to the end of the tail. 



6. Of the vertebrae, the DORSAL, as the simplest of those in 

 front of the tail, may first be selected for description, the fifth 

 dorsal being taken as the type. The centrum of this vertebra (c) 

 is about three quarters as deep from above downwards as it is 

 broad from side to side, its length (from before backwards) being 

 about equal to its breadth. Its upper surface is more or less flat- 

 tened. Its under surface is strongly convex from side to side, 



