46 



ANATOMY OF VERTEBRATES. 



fissure deepens and tlic 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 hasmal arch. There are no true 



40 hasmajDophyses in the tail of fishes : the elements there 



composing the hajmal arch are parapophyses, pleura- 



pophyses, or iDoth combined. In the abdomen only are 



hasmapophyses represented by the supporting bones of 



the ventral fins, fig. 41, e4. The slender ossicles 



along its under part in the Hemng, fig. 37, dli, are 



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



connected with the lower ends of the riljs, jjl- 



In the subclass Protopteri the notochord, fig. 41, 

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

 the hajmal 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 

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

 hasmal arch and support the hajmal spines, hs, along 

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

 velopes in the continuous vertical fin-fold the acces- 

 sory ossicles marked m, ili, in the cut. 



§ 18. Vertehral column of Batrachia. — Xcither 

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

 cephalan or batrachian. In the former amphiljious 

 order the notochord persists, but with Ijeginnings of 

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

 verted into a series of separate centrums. These in 

 the Ichtliyomorphs are biconical, and deeply cupped 

 at Ijotli ends, through the same arrest of ossification 

 as in fishes : the developemeut of the vertebra goes 

 through tlie same piscine stage in the larvre of the 

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

 42 ; in tlie mature quadrupedal stage of these Ba- 

 trachia, ossification converts one terminal cup into a 

 ball ; which may l)e the front one, as in Pipa, or the 

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

 the Land- Salamander, also, ossification goes to this 

 stage, with the ball in front. 



I'liidd-iiTii] exii-ske- 

 Ictal L'k'iiieiits (il II 

 t'fiudal vt'rtflirii of 

 tliG riakc, II. 



' Loctuvcs OH Coiiip. Aunt. p. 191, I'ig. 81. 



