DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 43 



everywliere in this outwiirdly similar, but inwardly most variable, " Order." The 

 determination of these will, I am satisfied, help the Zoologist in his work of deter- 

 mining species and classifying the gi'oups. 



10. Rana j)yci'>n(Pa. — Adult male; 7} inch long. Anamallays Mountains, Malabar, 

 S. W. India. 



I shall, in turn, describe the skull of a true Frog as small as this from the Ethiopian, 

 and of a sub-typical form from the Neotropical region ; they will appear like the 

 yowig of larger species ; this is manifestly old and its skull is intensely ossified 

 (Plate 5, figs. 11-15). 



This is a very short skull ; in R. gracilis and R. ci/anophlyctis the width of the skull 

 aci-oss the quadrato-jugals is exactly the same as the length. In tliis species the 

 breadth is to the length as 4 to 3^. 



In R. cyanophlyciis the condyle of the quadrate ends opposite the exit of the 9th 

 nerve ; in R. gracilis it ends opposite the same point ; in R. pygmcea it does not reach 

 further back than the front third of the stapes — two-fifths of the distance between 

 the 5th and 10th nerves, at their exit. The extremest case of wide gape is in 

 R. pipiens, where this joint is far behind the occipital condyles (see Plate 8). 



This is almost the only sign of arrest in the skull of this small, stout species,* but 

 there are some things in it which have a look of generalisation about them, as if this 

 were an old offshoot from the stock. 



The occipital condyles {oc.c.) are oval, small, and very wide apart ; the emargination 

 of the roof, over tlie foramen magnum {/.in.) is slight ; that of the floor is a mere 

 gentle arcuation of the transverse margin of the skull-floor. 



The whole cranium, proper, is flat and wide, only gently narrowing in at the temples, 

 and a little more in front of the eyes ; thus the ear-masses ai'e wide apart, and with 

 their drums outside and a little in front of them, have a very elegant appeai-ance 

 (Plate 5, fig. 11). These four regions are nearly of the same size. 



The common bony occipito-auditory mass is cleft in its fore margin below (fig. 12), 

 and bi-emarginate in its fore margin above (fig. 11). This widely extended post- 

 cranial region is capped with cartilage at three y)laces on each side. These unossified 

 tracts are — a, the occipital condyles (oc.c.) ; h, the edge of the tegmen tympani 

 (fig. 11, t.ty) ; and c, the facets for the "pedicle" below (fig. 12, pc/.). The roof- 

 cartilage has evidently been absorbed considerably, between the temjaoral regions, thus 

 the three fontanelles all inn into one, which is an oval, with rounded lobes behind. 



The alisphenoidal region is ossified half way to the optic opening (II.) ; the girdle- 

 bone {elh.) just reaches that passage in front ; thus there is a half belt of cartilage in 



♦ I am of opinion that tbere are forms which, although highlj- specialised, are ari-cstcd as compared to 

 their large nearest congeners ; this must be dne to dwarfing, and is to be distinguished from archaic, 

 or truly generalised conditions. 



G 2 



