DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 51 



Its regions, fore, middle, and hinder, are in contrast with Avhat is seen in the two 

 Bull-frogs just described and also in the lesser species, for the middle region is long, 

 relatively, beyond that of any kind I know, each orbital region being large enough to 

 ensocket a pair- of eye-balls twenty times the size of those that do lodge in them. 

 This middle region shows a cranial trough, not high (fig. 8) but narrow, and with an 

 approach to the outline of an hour-glass. 



The length is a fraction less than the greatest breadth, and the quadrate condyles 

 (q.c.) just reach to a supposed hue running across the double hole for the 9th and 10th 

 nerves (IX., X.). 



Thus the gape is not that of a very characteristic Frog, but rather that of an arrested 

 or a somewhat generalised type. Laterally seen (fig. 8), the skull is arched, having 

 strong deep curved planks of bone built round and over it : this is a correlate of its 

 powerful mandible with its inimetic canine tooth {d.). Everything in the side view 

 speaks of strong pterygoid and temporal muscles. 



The outer bones are unusually strong, so are the intermediate pterygoids (p^.), but 

 the ossification of the endocranium is exactly like that of an adult Common Frog, and 

 very mferior in degree to what is seen in the two lax'ge kinds, and in the dwarft species 

 [R. pygmcea, Plate 5, figs. 11, 12), 



The occipital condyles [oc.c.) are large, low in position, near together, and with 

 the short interspace straight. There is a considerable basi- and supraoccipital tract 

 unossified, and the prootics and ex-occipitals [pr.o., e.o.) are divided below, and only 

 slightly confluent above. 



There are the three normal fontanelles above, and the side walls (fig. 8) are w^ell built 

 up to the roof, under the edges of wiiich there is on each side a very definite "wail- 

 plate." The arched form of the skull is combined with considerable overlaj^ping of the 

 roof and floor (figs. 7, S,/.p., j^fi-s.), the investing bones being applied above and below 

 very closely round the endocranium [etJi., o.s.) so as to leave the interorbital wall 

 uncovered to an unusually small extent. The short and not very broad nasal region lies 

 well within the outer bones; there is no "rostrum," but the pro-rhinals (jj.rh.) are tPell 

 developed and unusually long and projecting; the labials («,/'.«./-.) are normal. The 

 "girdle-bone" (eth.) reaches only to the front of its own region and half-way back to the 

 optic nerves; it does not ossify the very definite angular supraorbital projection (s.ob.), 

 which here attains to a distinctness almost equal to what it has in the "Hylidre." 



The more rounded form of the great orbital space in front, enclosed there by the 

 ethmo-palatine bar, gives rise to a sickle-shaped palatine bone (^J".), and this is 

 followed at the outer edge by a very remiukable pterygoid (^f/.). The pi-ocesses of 

 this bone that enwrap the pedicle (pd.), and bind upon the inside of the suspensorium 

 to the hinge {q.c), are short but normal, but the intra-jugal portion of the bone is of 

 great depth (fig. 8, pg-), and strongly inbeut. 



In the "axU" of the pterygoid the Eustachian passage is small and round; the 

 stylo-hyal end of the hyoid {st.Ji.) has coalesced with the tynijianic floor, and bends 



U -2 



