46 THE CAT. [CHAP. in. 



are placed directly over the ventral sacral foramina before described. 

 The bony substance of each sacral vertebra projects outwards beyond 

 these foramina, forming what is called the " lateral masses " of the 

 sacrum (/), which are in fact the coalesced transverse processes of 

 the sacral vertebrae. 



The formation of the ventral and dorsal sacral foramina may be 

 thus explained. Nerves in the true vertebra? pass out, as we have 

 seen, between the pedicles of adjacent vertebra?. Now the coa- 

 lescence of the sacral transverse processes necessarily changes each 

 such intervertebral opening into a pair of openings, of which one is 

 dorsal and the other ventral. 



In a line connecting each pair of dorsal sacral foramina, slight 

 irregular perforations in the roof of the neural canal indicate the 

 primitive interspaces which existed between adjacent sacral vertebra?. 

 At the anterior end of the sacrum is an articular surface (c), 

 very wide but narrow from above downwards, which joins the 

 centrum of the last lumbar vertebra. Above this is the opening of 

 the neural canal, also greatly extended transversely, and narrow 

 from above downwards, and the prezygapophyses and neural spine 

 before mentioned. Extending out from each side of the front 

 articular surface of the centrum are the two " lateral masses," which 

 project strongly outwards, downwards, and somewhat forwards. 



At the posterior end of the sacrum there is a small oval articular 

 surface, which joins the centrum of the first caudal vertebra. On 

 each side of it the "lateral masses" here small, thin bony plates 

 project outwards. Above it is the small crescentic opening of the 

 hinder end of the sacral neural canal, surmounted by the neural 

 spine and postzygapophyses (z) before mentioned. 



The sacrum, viewed laterally, exhibits the neural spines, zyg- 

 apophyses, and dorsal foramina before described, and below these, 

 one of the lateral masses, which appears deep in front and tapers 

 rapidly backwards. On its deep part is a large irregular surface, 

 which in the living animal is coated with cartilage, and articulates 

 with the hip or haunch- bone. This surface is somewhat crescentic, 

 with the concavity upwards, and is called the auricular surface, because 

 the corresponding part in man has an outline somewhat resembling 

 an ear. Above this surface the lateral mass is more or less excavated 

 and uneven. The auricular surface may be entirely supported by that 

 part of the lateral mass which pertains to the first sacral vertebra; it 

 may, however, extend on to part of that pertaining to the second 

 sacral vertebra. That part which pertains to the third sacral vertebra 

 ends behind in a pointed process extending outwards as well as 

 backwards to about the level of the middle of the sacrum's hinder 

 central surface. 



12. The last part of the cat's spine is formed by the CAUDAL 

 VEUTEBEJE (see Fig. 23), usually about eighteen or nineteen in 

 number, but sometimes as many as twenty-four. Of course the 

 short-tailed breeds have only a few caudal vertebra?. In the Manx 

 cat there are four, and in the Malay cat several of the vertebra? 



