28 



ANATOMY OF VERTEBRATES. 



18 



Cranial sogmcii^or vertoljia 



throughout the vertebrate series; and some parts, usually, exo- 

 genous, are autogenous in a few instances. 



The vertebral elements are, the centrum 

 c, the neurapophyses n ; the neural spine 

 ns, the pleurapophyses pi, the Ivccmapo- 

 physes /(, and the haimal spine hs. The 

 exogenous parts are the diapophysis d, the 

 parapophysis;), the zygapophysis r,' the ana- 

 popliysis «,^ the metapophysis m,^ the hypa- 

 jiophysis, fig. 17, y,"* and the epapophysis, 

 fig. 17, e.^ Of the autogenous parts, the 

 neural spine is most commonly exogenous; 

 of the exogenous parts, the parajiophyses, 

 diapophyses, and hypapophyses, are sometimes autogenous. 



Vertebra3 are suliject to many and great modifications — e. g. as 

 to the number of the elements retained in tlieir composition, as to 

 the form and pro2:)ortion of the elements, and e^'en as to the relative 

 position of the elements ; but the latter modification is never 

 carried to such a degree as to obscure the general pattern or 

 type of the bony segment. 



Sometimes, as in the example, fig. 18, of the third segment of 

 the human skeleton, tlie neural arch, N, is much expanded, the 

 hcBmal one, ii, is contracted; and, in the expanded neural arch, 

 the autogenous diapophyses, d d, are wedged between the neura- 

 pophyses, n, and the enormously expanded neural spine, ns. IMore 

 19 commonly, as in the example from the thorax, fin-. 



19, the ]ia3mal arch, /;.«, is much expanded, the neural 

 one n, contracted; and the parapophysis is re]>re- 

 sented somethnes by tlie exogenous growth from 

 the centrum, commonly by that, p, from the ril) pi. 

 Sometimes, again, as is exemplified in the neck of 

 the bird, fig. 20, and tlie tail of the Crocodile, both 

 neural and luvmal arches arc alike contracted, the 

 pleurapophyses, /)/, being excluded from the latter, 

 and standing out as continuations of the confluent 

 diapophyses and parapopliyses ; and the ha?mal arch 

 l)eing formed, either liy ha-majiopliyscs (Crocodile), fig. 7, or 

 hypapophyses (bird), fig. 20, /,//. Such vertebra deviate but 

 little from the ideal type, under its less developed condition, 

 as in fig. 7. The segments arc commonly simplified and made 



' Gr. j«f/,«, jmictioii, ,iu,l apvphiisis. • Qr. /,„/„,, l,,loiv, and „pophi,sis. 



- Gr. ami, backwai-ds, ami ,v«7./,».v/.v. f Qr, cj,i, above, an.l „p,:ph„yis. 



^ Gr. iiict(/, bctwcon, iiiul ftpojiliusis. 



^xrlulira 



