GENERAL CHARACTERS OF VERTEBRATA. 3<DI 



there are also developed in the typical vertebra two processes 

 (a a), which are known as the "articular" processes, or "zyga- 

 pophyses." The vertebrae are united to one another partly 

 by these, but to a greater extent by the bodies or " centra." 

 From the sides of the vertebral body, at the point of junction 

 with the neural arches, there proceed two lateral processes 

 (d d), which are known as the " transverse processes." 



Fig. 268. A, Lumbar vertebra of a Whale : c Body or centrum ; n n Neural arches ; 

 j Neural spine ; a a Articular processes ; d d Transverse processes. B, Diagram of a 

 thoracic vertebra : c Centrum ; n n Neural arches enclosing the neural canal ; J Neural 

 spine; r r Ribs, assisting in the formation of the haemal arch; j> p Costal cartilages; 

 b Sternum, with haemal spine. (After Owen.) 



These elements form the vertebra of the human anatomist, 

 but the "vertebra" of the transcendental anatomist is com- 

 pleted by a second arch which is placed beneath the body of 

 the vertebra, and which is called the " haemal " arch, as it 

 includes and protects the main organs of the circulation. 

 This second arch is often only recognisable with great diffi- 

 culty, as its parts are generally much modified, but a good 

 example may be obtained in the human chest, or in the caudal 

 vertebra of a bony fish. 



As a general rule, the vertebral column is divisible into a 

 number of distinct regions, of which the following are recog- 

 nisable in man and in the higher Vertebrata : i. A series of 

 vertebrae which compose the neck, and constitute the " cer- 

 vical region " of the spine (fig. 269, c\ 2. A number of vertebrae 

 which usually carry well-developed ribs, and form the " dorsal 

 region'' (d). 3. A series of vertebrae which form the region 

 of the loins, or "lumbar region" (b}. 4. A greater or less 

 number of vertebrae which constitute the " sacral region," and 



