28 



ANATOMY OF VERTEBRATES. 



genous, 



18 



7tS 



C'ranial scginen or vertebra 



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

 are autogenous in a few instances. 



The vertebral elements are, the centrum 

 c, the neurapophyses n ; the neural spine 

 ns, the pleurapophyses pi, the haemapo- 

 physes h, and the haemal spine hs. The 

 exogenous parts are the diapophysis d, the 

 parapophysis/*, the zygapophysis z, } the ana- 

 pophysis a, 2 the metapophysis m, 3 the hypa- 

 pophysis, fig. 17, y, 4 and the epapophysis, 

 fig. 17, e. 5 Of the autogenous parts, the 

 neural spine is most commonly exogenous; 

 of the exogenous parts, the parapophyses, 

 diapophyses, and hypapophyses, are sometimes autogenous. 



Vertebrae are subject to many and great modifications e. g. as 

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

 the form and proportion of the elements, and even 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, the neural arch, N, is much expanded, the 

 hsemal one, H, 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. More 

 commonly, as in the example from the thorax, fig. 

 1 9, the haamal arch, hs, is much expanded, the neural 

 one n, contracted ; and the parapophysis is repre- 

 sented sometimes by the exogenous growth from 

 the centrum, commonly by that, p, from the rib pL 

 Sometimes, again, as is exemplified in the neck of 

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

 neural and haemal arches are alike contracted, the 

 pleurapophyses, pi, being excluded from the latter, 

 and standing out as continuations of the confluent 

 diapophyses and parapophyses ; and the hcemal arch 

 being formed, either by haemapophyses (Crocodile), fig. 7, or 

 hypapophyses (bird), fig. 20, hy. Such vertebras deviate but 

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

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



Thoracic segment or 

 vertebra 



1 Gr. zugos, junction, and apophusis. 



2 Gr. ana, backwards, and apophusis. 



3 Gr. meta, between, and apophusis. 



Gr. Jnipo, below, and apophusis. 

 Gr. epi, above, and apophusis. 



