CERVICAL VERTEBRA. 23 



times of great size and strength, but varies much in development 

 in the different regions of the same animal. The inferior 

 (hypapophyses) are for the most part rudimentary, and can 

 scarcely be said to exist, except in the cervical region, where 

 they project from the inferior central line of the bodies. 



The centra or bodies of the vertebrae, placed in natural appo- 

 sition, thus form a central bony column, to which the arches 

 and processes are attached ; the arches, with their connecting 

 ligaments, form superiorly a cavity, the spinal or neural canal, 

 which extends from the head to the tail, and contains the spinal 

 cord, with its membranes and blood-vessels ; the articular pro- 

 cesses strengthen the connections of the vertebrae, while the 

 spinous and transverse processes are levers to which muscles are 

 attached, their development having great influence on the physical 

 conformation and capabilities of the animaL The ribs may be 

 regarded as continuations of the dorsal transverse processes ; they 

 help to form the inferior or haemal arch of their own region. 



FALSE VERTEBRAE. 



The false vertebra are found in the sacrum, which con- 

 sists of vertebral segments united by the ossification of their 

 connecting material, and in the coccyx, the skeleton of which 

 consists of rudimentary or imperfectly-developed vertebrae. The 

 sacral segments in the early stages of life are separable, and 

 they present all the characteristics of true vertebrae. 



CERVICAL VERTEBRAE. 



General Features. 



(FiG. 8.) 



There are seven cervical vertebra in all the Mammalia, with 

 the exception of the Three-toed Sloth, which has nine, and one of 

 the Sea-cows, which has six. They are numbered in order from 

 the head, the first receiving the special name of atlas, and the 

 second that of axis or vertebra denata ; these, with the sixth and 

 seventh, differ from the rest, which are essentially alike. 



The centra or bodies of the cervical vertebrae are larger and 

 longer than those of any other true vertebrae, and frequently 

 measure upward of four inches in length ; they are quadrangular 

 in shape, their anterior extremity or head being convex and some- 

 what heart-shaped, with the apex downwards, while the postericr 



