140 



MORPHOLOGICAL TYPES 



shaft or diaphysis and an epiphysis at each end. Between the 

 epiphyses and the diaphysis there are, in young mammals, 

 portions of cartilage, and the bone is able to increase in length 

 by adding on new bone to the diaphysis at each end. Eventu- 

 ally, however, the epiphyses become firmly fused on to the 

 diaphysis, and no further growth of the bone is then possible. 



Fig. 61. — Lepus : thoracic vertebras and ribs. 



A, seen from in front ; B, seen from the left side, c, centrum of the 

 vertebra ; ca, capitulum of the rib ; na, neural arch ; ns, neural spine ; r, 

 rib ; t, tuberculum of the rib ; tp, transverse process. 



The epiphyses can still, however, be recognised as distinct 

 from the diaphysis. 



Vertebral Column. — In all mammals the number of cervical 

 vertebrae is seven (three species only form an exception to this 

 rule). The first is the centrum-less atlas, and the second is 

 the axis bearing the centrum of the atlas in the form of the 

 odontoid peg. The cervical vertebrae have vertebrarterial 

 canals formed by the fusion of the tuberculum of the rib to the 



