328 



MANUAL OF ZOOLOGY. 



rapophyses," because they form with the body a canal the 

 " neural canal " which encloses the spinal cord. From the 

 point where the neural arches meet behind, there is usually 

 developed a longer or shorter spine, which is termed the " spi- 

 nous process " or " neural spine " (s). From the neural arches 

 there are also developed in the typical vertebra two processes 

 (aa\ which are known as the " articular " processes, or " zyga- 

 pophyses." The vertebrae are united to one another partly by 

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

 the side 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." (In the typical 

 vertebra the transverse processes consist each of two pieces, 

 an anterior piece or " parapophysis," and a posterior piece or 

 " diapophysis.") These elements form the vertebra of the 

 human anatomist, but the " vertebra " of the transcendental 

 anatomist is completed by a second arch which is placed be- 

 neath the body of the vertebra, and which is called the " hae- 

 mal " arch, as it includes and protects the main organs of the 

 circulation. This second arch is often only recognisable with 

 great difficulty, 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. 



Fig. 117. A, Lumbar vertebra of a Whale: c Body or centrum ; n n Neural arches ; 

 s Neural spine ; a a Articular processes ; dd Transverse processes. B, Diagram of a 

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

 Neural spine ; r r Ribs, assisting in the formation of the haemal arch ; pp Costal car- 

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



The haemal arch in the case of the human thorax (fig. 117, 

 B) is formed by the ribs (r r) and the costal cartilages 



