DEVELOPMENT OF THE SKULL IN THE I3ATRACHIA. 
51 
Its regions, fore, middle, and hinder, are in contrast with what 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 line 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 mimetic canine tooth (cl). Everything in the side view 
speaks of strong pterygoid and temporal muscles. 
The outer bones are unusually strong, so are the intermediate pterygoids (pg.), but 
the ossification of the endocranium is exactly like that of an adult Common Frog, and 
very inferior in degree to what is seen in the two large kinds, and in the dwarft species 
(di. 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 pi’ootics 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 well built 
up to the roof, under the edges of which there is on each side a very definite “ wall- 
plate.” The arched form of the skull is combined with considerable overlapping of the 
roof and floor (figs. 7, 8,f.p., pa.s.), the investing bones being applied above and below 
very closely round the endocranium (eth., 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 ( p.rh .) are well 
developed and unusually long and projecting; the labials (u.V.u.V 1 .) are normal. The 
“girclle-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.oh.), 
which here attains to a distinctness almost equal to what it has in the “Hylidse.” 
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 (pa.), and this is 
followed at the outer edge by a very remarkable pterygoid (pg.). The processes 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 inbent. 
In the “axil” of the pterygoid the Eustachian passage is small and round; the 
stylo-hyal end of the hyoid (st.h.) has coalesced with the tympanic floor, and bends 
li 2 
