28 



ANATOJIY OF VERTEBRATES. 



18 



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

 genous, are autogenous in a few instances. 



The vertebral elements are, the centrum 

 c, the nenrapophyses n ; the neural spine 

 ns, the plenrapophyses pi, the hsemapo- 

 physes h, and the haemal spine hs. The 

 exogenous parts are the diapophysis d, the 

 parapophysis/>, the zygapophysis z, 1 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 



d 

 fi 



W&bP% 



its 



Cranial segmen or vertebra 



neural spine is most commonly exogenous; 

 of the exogenous parts, the parapophyses, 

 diapophyses, and hypapophyses, are sometimes autogenous. 



Vertebra? 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 

 haemal 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 hamial 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 pi. 

 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 haemal arch 

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

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

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

 The segments are commonly simplified and made 



^n^ 



V 5 



Thoracic segment or 

 vertebra 



as in fig. 7. 



1 Gr. zugos, junction, and apophusis. 



2 Gr. ana, backwards, and apophusis. 



3 Gr. meta, between, and apophusis. 



Gr. hupo, below, and apophusis. 

 Gr. epi, above, and apophusis. 



