ANATOMY OF RA^'A TrGHTNA. 



605 



A comparison of the neural arch of a typical (e. g. sixth) 

 vertebra of the grass-frog with that of the corresponding 

 vertebra of R. tigrina or of Pelohates fascios, will, I think, bear 

 out this statement (text-fig. 2, A-C). 



In all three cases it will be seen that there is an incisure upon 

 the anterior face of the neural arch between the zygapophyses. 

 In the Bull-frog and in Pelohates this incisure is a deep one, 

 whereas in R. temjMraria it is broad but comparatively shallow. 

 Upon its posterior border the arch is practically not incised at all 

 in R. teriiporaria, aud is most deeply notched in Pelohates, the 

 condition of R. tigrina being intermediate in this respect. 



Text-figure 2.- 



V^ 



The sixth vertebra of (A) Rana tigrina (X |), (B) H. temporaria, and (C) Pelo- 

 hates fasctis (both X 3), to show the relative decree of incisure of tlie neural 

 arches and the development of the neural spiu?s iu the three species. («) Dorsal, 

 (6) ventral, and (c) posterior view. 



In Pelohates and in R. tigrina, however, the centrum has 

 practically the same length as the neural arch, whereas in R. tem- 

 poraria the centrum is, approximately, half as long again as the 

 neural ai'ch. When the vertebra3 are articulated in the normal 

 manner, therefore, the neural arches do not come into contact in 

 this species, excepting at the zygapophyses, notwithstanding that 

 some of the surplus length of the centrum has been absorbed in 

 the concavity of the following centrum. In the case of R. tigrina 

 (and Pelohates) the neural arch is sufficiently long to allow of 

 considerable overlap upon the succeeding neural ai^ch. 



Neural spines, too, are well developed (text-figs. 1, 2). This 

 Proc. Zool. Soc— 1915, Xo. XLIT. 42 



