A treatise on zoology . teral radials ;but small preaxial radials remainin Protopferus (Fig. 205). The fin-skeleton is entirely of Ceratodus ForstcH, Kr. The skeleton of ^ in livinf Dinnoi andthe right fin is completely exposed, a, jointed CartUaglUOU., Ul llVUlj^ l^ipnoi, dliu axis ; , dermal rays ; , lateral process ; scarcely any traCCS of it , median process; p, pelvic cartilage; . i <? -i a- ;»•.(•, postaxial radials; , preaxial radials; in any KUOWU lOSSllS. hinCC, s, scaly covering of axial region. (Partly Virvwo-irov fVit^oo liavA nil Inhntpafter Bsw
A treatise on zoology . teral radials ;but small preaxial radials remainin Protopferus (Fig. 205). The fin-skeleton is entirely of Ceratodus ForstcH, Kr. The skeleton of ^ in livinf Dinnoi andthe right fin is completely exposed, a, jointed CartUaglUOU., Ul llVUlj^ l^ipnoi, dliu axis ; , dermal rays ; , lateral process ; scarcely any traCCS of it , median process; p, pelvic cartilage; . i <? -i a- ;»•.(•, postaxial radials; , preaxial radials; in any KUOWU lOSSllS. hinCC, s, scaly covering of axial region. (Partly Virvwo-irov fVit^oo liavA nil Inhntpafter Bswidotr, from Quart. Jonrn. ) nOWeVCl, tnese liaVC all lODaiG fins like those of Ceratodus, therecan be hardly any doubt, judging from the scale-covered axialregion, the dermal rays, and what remains of the axis in somefossils, that the endoskeleton in the extinct Dipnoi was of essen-tially similar character. It may safely be assumed that theearly forms had typical rachiostichous and mesorachic Fio. view of the pelvic girdle and lins BRAIN 245 The brain deserves particular notice :few organs in the Dipnoi so clearly showthe isolation of this sub-class from otherfish. On the whole, the brain is primitivein structure ; it lacks the special character-istics of the Elasmobranch or of the Teleo-stome ; so far as it is distinctly advanced,it approximates to the Amphibian type(Beauregard [35], Burckhardt [69], Bingand Burckhardt [73]). The brain is longand narrow, and has large ventricles. Alarge and simple medulla is followed by avery small cerel)ellum (Figs. 214-15). Themid-brain is long and fully exposed ; theoptic lobes are fused in Protopterus. Thereis a velum transversum. ]\Iost remarkableare large paired cerebral prolongationsprojecting far beyond the lamina hemispheres are separate, and inthe Dipneumones have thickened nervouswalls above and at the sides as Avell asbelow (Fig. 281); in Ceratodus, however,which has a less d
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