15° 



CHORDATE ANATOMY 



EPISTROPHEUS 



CERVICAL ,' 

 CURVATURE^ 



}'CERV1CAL 



the foramina for the spinal nerves which pass out between the vertebrae. 

 Articular processes or zygapophyses project forwards and backwards 

 from the neural arches. A postzygapophysis of one vertebra overlaps a 

 prezygapophysis of the next vertebra and the two are bound together by 



ligaments: thus the backbone is 

 strengthened, but at the same time 

 made less flexible. On each side a 

 transverse process projects from the 

 neural arch laterally into the muscles 

 of the body wall. 



The Kinds of Vertebrae. There 

 are five kinds of vertebrae, cervical, 

 thoracic, lumbar, sacral, and caudal 

 or coccygeal. A distinguishing fea- 

 ture of cervical vertebrae is a trans- 

 verse foramen which in the upper 

 six vertebrae transmits the vertebral 

 artery. The lateral border of this 

 foramen is formed by the fusion of a 

 rudimentary rib with the vertebra. 

 The first two cervical vertebrae are 

 the atlas and the axis or epistro- 

 pheus. A pecuUarity of the two is 

 that the centrum of the atlas fuses 

 with that of the axis to form the 

 odontoid process upon which the 

 atlas rotates. The forms and 

 arrangement of the cervical verte- 

 brae permit greater freedom of move- 

 ment than is possible in other parts 

 of the column. The spinous process 

 of each cervical vertebra except the 

 last is forked or bifid. 



Only the twelve thoracic verte- 

 brae carry ribs. A pit in the cen- 

 trum articulates with the head of the 

 rib and a similar pit at the extremity of the transverse process articulates 

 with the tubercle of the rib. The head of most ribs articulates with two 

 adjacent centra. 



The five lumbar vertebrae are the largest. Short ribs fuse with them 

 to form conspicuous transverse processes. The neural arches of these 

 vertebrae have mammillary and accessory processes in addition to 

 articular. 



Coccygeal. 



Fig. 140. — The human vertebral col- 

 umn viewed from the left side. (Redrawn 

 after Sobotta.) 



