SKELETON AND TEETH 



73 



ptz 



Fig. 15. — Third lumbar vertebra of Wolf, 

 front end and left side. Ir., transverse 

 process, en., centrum, pr.z. and pl.z., 

 anterior and posterior zygapophyses. 

 n.sTp., neural spine. 



rately so. Taking the dorso- 

 lumbars, or trunk-vertebrae, as a 

 single series, we may note that 

 in a few mammals {e.g. the ele- 

 phants) all the neural spines 

 have a backward slope, but in 

 the great majority of forms 

 this backward inclination ceases 

 near the hinder end of the dor- 

 sal region, where there is one vertebra with erect spine, while 

 behind this point the spines slope forward. 



(4) The sacral vertebrae, varying from 2 to 13 in number, 

 are fused together solidly into one piece, the combined centra 

 forming a heavy mass and the neural canals a 

 continuous tube, while the neural spines are 

 united into a ridge. As a rule, only the first 

 two vertebrae of the sacrum are in contact with 

 the hip-bones, to support which they have de- 

 veloped special processes, the remainder of the 

 mass projecting freely backward. 



(5) The caudal vertebrae vary greatly, in 

 accordance with the length and thickness of the 

 tail. In an animal with well-developed tail 

 several of the anterior caudals have the parts 

 and processes of a typical vertebra, centrum, 

 neural arch and spine, zygapophyses and transverse processes. 

 Posteriorly, these gradually diminish, until only the centrum 

 is left, with low knobs or ridges, which are 

 the remnants of the various processes. A 

 varying number of long, cylindrical centra, 

 diminishing backward in length and diame- 

 ter, complete the caudal region and the ver- 

 tebral column. In some mammals, chevron 

 bones are attached to the under side of the 

 anterior and middle caudals ; these are forked, Y-shaped bones, 



Fig. 16. — Sacrum 

 of Wolf, upper 

 side. /, //, ///, 

 first, second and 

 third sacral verte- 

 brae. pL, surface 

 for attachment to 

 hip-bone. 



Fig. 17. — Caudal verte- 

 brae of Wolf, from ante- 

 rior and middle parts of 

 the tail. Letters as in 

 Fig. 15. 



