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General Observations on the Skeletons of the BATRACHIA. 



In commencing the study of the skeletons of Reptiles in the lowest, and most fish-like of the class, 

 we find a much less complex condition of the osseous framework of the body than in the Bony Fishes ; 

 this will be immediately manifest by a comparison of the skeleton of the Menopome (No. 583), which 

 may be taken as an example of the perennibranchiate Batrachia, with the skeleton of the Trout 

 (No. 45), or of the Haddock (No. 176). 



The difference tends greatly to elucidate the true nature of the complexities of the Fish's skeleton, 

 since it chiefly consists in the simplification of that of the Batrachian by the non-development of the 

 parts of the dermal skeleton, which characterize that of the Fish. The suborbital, supraorbital and 

 supratemporal scale-bones are removed, together with the opercular bones from the head ; and the 

 interneural and dermoneural spines, with the interheemal and dermohaemal spines, are removed from 

 the trunk : and the endo-skeleton is also reduced to a very simple condition ; the advance characteristic 

 of the higher class being appreciable only by a comparison of it with the skeleton of the most batrachoid 

 of Fishes the Protopterus (No. 380) and Lepidosiren. 



We then perceive that the bodies of the vertebrae, in the true Batrachian, are distinctly ossified, 

 though preserving, in the perennibranehiate species, a deep, conical, jelly-filled cavity both before and 

 behind : they have also coalesced with the neural arches, as these have with their spines, which are, 

 however, scarcely developed except in the tail. The transverse processes are developed not only 

 from the centrum but from the base of the neural arch, and are formed by both parapophyses and 

 diapophyses ; and they coexist with distinct heemapophyses in the tail : with these, likewise, coexist 

 cartilaginous pleurapophyses in the second, third and fourth caudal vertebrae ; short ossified pleur- 

 apophyses being developed from the ends of the diapophyses in the first caudal to the vertebra dentata 

 inclusive. 



By this instructive condition of the skeleton of the Menopome we perceive at once that the haem- 

 apophyses are neither transverse processes, nor ribs bent down or displaced, but are elements of vertebrae, 

 as distinct as the neurapophyses above. The neural arches are now articulated together by well- 

 developed zygapophyses with synovial articulations, which are absent in the Protopterus, as in most 

 Fishes. 



In the Protopterus, as in the Squatina and some other cartilaginous fishes, the neural arch of the 

 atlas rests upon a backward production of the basioccipital ; in the Batrachians it is confluent with 

 its own proper centrum, which developes two articular surfaces for two occipital condyles. The 

 haemal arch of the occipital segment which is attached to its proper vertebra in the Lepidosiren, as 

 in Osseous Fishes, is detached and displaced backwards in the Batrachians, as in the Plagiostomes. 

 In the completion of the haemal arch of the sacral vertebra in the Menopome, by the enlarge- 

 ment of its transverse process and by its pleurapophysis extended to join a heemapophysis below, we 

 have the key to the essential nature of the pelvis in all air-breathing animals. The ultimate subdivi- 

 sions of the radiated or diverging appendages of the scapular and pelvic arches do not exceed five in 

 any existing air-breathing animal, and their further complexity is due to the specialization of each digit, 

 so as to combine in associated action, instead of their indefinite multiplication which causes the seeming 

 complexity of the same appendages in Fishes. 



