46 



ANATOMY OF VERTEBRATES. 



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fissure deepens and the fork elongates, until at the seventy-third 

 the lower prong descends at a right angle to the upper one, and, 

 meeting its fellow, forms the hamial arch. There are no true 

 40 hrcmapophyses in the tail of fishes : the elements there 



composing the luemal arch are parapophyses, pleura- 

 pophyses, or both combined. In the abdomen only are 

 hremapophyses represented by the supporting bones of 

 the ventral fins, fig. 41, 64. The slender ossicles 

 along its under part in the Herring, fig. 37, dh, are 

 dermal bones, which, like the scutes of serpents, are 

 connected with the lower ends of the ribs, pi. 



In the subclass Protopteri the notochord, fig. 41, 

 ch, persists : the neural arches, n, ns, are ossified : 

 the haemal arches in the abdomen are represented 

 by parial bones, p, attached to the notochordal sheath, 

 and curving outward, like the long parapophyses in 

 the Cod, and the short pleurapophyses in the Amia 

 and Salamander, with which they, more probably, 

 are homologous. These riblets bend down and 



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meet at the beginning of the tail, p, to form the 

 ha3inal arch and support the ha3inal spines, hs, along 

 that region. As in fishes, the Lepidosiren also cle- 

 velopes in the continuous vertical fin-fold the acces- 

 sory ossicles marked in, ih, in the cut. 



18. Vertebral column of Batrachia. Neither 

 inter- nor dermo-neurals are present in any gano- 

 cephalan or batrachian. In the former amphibious 

 order the notochord persists, but with beginnings of 

 the ossification of centrums : } in Batrachia it is con- 

 verted into a series of separate centrums. These in 

 the Ichthyomorphs are biconical, and deeply cupped 

 at both ends, through the same arrest of ossification 

 as in fishes : the developement of the vertebra goes 

 through the same piscine stage in the Iarva3 of the 

 Theriomorphs, as indicated by the dotted lines d, fig. 

 42 ; in the mature quadrupedal stage of these Ba- 

 trachia, ossification converts one terminal cup into a 

 ball ; which may be the front one, as in Pipa, or the 

 hind one, as in Rana, and most frogs and toads. In 

 the Land- Salamander, also, ossification goes to this 

 - and exo-ske- stage, with the ball in front. 



lotal elements of a 

 caudal vertebra of 

 the Plaice, n. 



1 Lectures on Comp. Anat. p. 194, Fig. 84. 





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