42 CERVICAL VERTEBRA. [CHAP. 



comparatively short, and not keeled, the laminae narrow, the 

 spines well marked, and the transverse processes greatly 

 developed, especially those of the atlas. 



In the Elephant (order PROBOSCIDEA), the atlas much 

 resembles the human atlas. The axis has a short conical odon- 

 toid process and a very massive spine, broad above and bifid 

 posteriorly. The bodies of the other vertebrae are very short, 

 flattened, sub-circular disks, very slightly opisthoccelous. 

 Excepting the seventh they all have short spinous processes, 

 and short, broad, and largely perforated transverse processes. 

 The seventh has a high spine, an imperforate transverse pro- 

 cess, and on the hinder edge of its body a very distinct arti- 

 cular cavity for the head of the first rib. In the young animal 

 this is divided into two equal parts by the neuro-central 

 suture. 



In the order SIRENIA, the Dugong (Halicore) has seven 

 cervical vertebrae, as in the Mammalia generally. The atlas 

 has short imperforate conical transverse processes. The axis 

 has a high arch and massive neural spine, a short rounded 

 odontoid process, and very rudimentary transverse processes. 

 The others have short and wide bodies, small spines, and 

 irregularly developed transverse processes, often not com- 

 pletely enclosing a vertebrarterial canal. 



The Rhytitta, a large animal of this order, which became 

 extinct towards the close of last century, had also seven 

 cervical vertebrae, and the Miocene Halitherium had the 

 same number. 



The Manatees (genus Manatus), of which there are two 

 well-marked forms, one inhabiting the west coast of 

 Africa, and the other the east coast of Central and South 

 America, never have more than six vertebras in the cervical 

 region. These resemble generally those of the Dugong, 

 having short and wide bodies, and very irregular transverse 



