TYPICAL SEGMENTS, OR VERTEBRAE, 



27 



by a pair of bones called "pleurapopbjses," pi (Gr, 

 pleuron^ rib, and apophysis) ; by 

 a second pair, called "baemapo- 

 pbyses," h (Gr. for blood, and 

 apophysis ; and by a bone some- 

 times bifid, called the "haemal 

 spine," hs. It also sometimes 

 includes parts, or bones, called 

 "parapophyses" (Gr. ^am, trans- 

 verse, and apophysis). Bones, 

 moreover, are developed, which 

 diverge as rays, from one or more 

 parts of a vertebra. 



The parts^of a vertebra which 



are developed from independent 



centres of ossification are called 



" autogenous ;" those parts that 



j grow out from previously ossified 



I parts are called " exogenous ;" the autogenous parts of a 

 ■ vertebra are its elements," the exogenous parts its " pro- 

 cesses." No part, however, is absolutely autogenous 

 throughout the vertebrate series, and some that are exo- 

 genous in most are autogenous in a few instances. The 

 line cannot be strictly drawn; and, in classifying the parts 

 of a vertebra, as of other parts of animals, or of entire 

 animals, the systematist must be guided by general rules, 

 to which there will ever be some exceptions. 



The elements, or autogenous parts, of a vertebra are 

 the centrum, c, the neurapophyses, n^ the neural spine, ns, 

 the pleur apophyses, pl^ the hcemapophyses, A, and the 

 haemal spine, hs. The exogenous parts are the diapophy- 

 sis (Fig. 5), d^ the parapophysis (ih) p^ the zygapophysis 

 (Fig. 6), z (Gr. zugos^ junction, and apophysis), the ana- 



TYPICAL VERTEBRA. — (iDEAL.) 



