Common Frog. 35 



For a full description of the Ophidian Skeleton, see Professor Owen, 

 Monograph on the Fossil Reptilia, pt. iii. p. ^^, 1 850. Hun- 

 terian Osteological Catalogue, Prep. 602 et seqq., 1853. Orr's 

 Circle of the Sciences, Organic Nature, vol. i. p. 196, 1834. 



For an account of the development of the two first cervical ver- 

 tebrae in Vertebrata Allantoidea, as discovered by Eathke, see 

 KoUiker, Entwickelungsgeschichte, p. 187, and H. Miiller, 

 cit. in loc. See also, Rathke, Entwickelungsgeschichte und 

 Korperban der Krokodile, p. 46, 1866. 



9. Common Frog {Ra^ia Temporaria), 



Injected and dissected so as to show its nervous, circulatory, and respiratory systems 

 together with some of its reproductive and digestive organs. 



The roof of the cranium, and the body- walls in front and on the 

 left side, have been removed with the integument and muscles in 

 connection with them. The reproductive appears to be the domi- 

 nant system in the economy of this and of the other Amphibians, 

 the sudden evolution of the generative glands, especially in the 

 females at the breeding season, necessitating certain special coor- 

 dinations and correlations in all, or nearly all, the other organs of 

 the body. The absence of complete costal arches may be explained 

 by the fact that great room must of necessity be available for 

 the lodgment of the ova previous to extrusion, and the trans- 

 pirability of the skin compensates in some measure for the sus- 

 pension of the function of the lungs which the great distension 

 of the thoracico-abdominal cavity entails at those periods. The 

 transpirability of the skin again exercises an important influence 

 on the special habits of these animals as it is incompatible with 

 the sustentation of life except in media containing a certain pro- 

 portion of watery vapour. The physiological importance of the 

 skm as an aerating and depurating organ, in correlation at once 

 with the kidneys and liver as well as with the lungs, is well shown 

 by the distribution of vessels to it as illustrated in Plate III. 

 The skin of the true Reptiles is far inferior in this point of view 

 to that of the Amphibia, which again is inferior to that of the 

 more highly organized classes in the all but universal absence of 

 scutes, scales and claws, and the universal absence of any of those 



D 2 



