92 MR. \V. K. I'AHKKR (IN THR STRUCTrRK AND 



manifestly seen to be an external crest of the trabecula, a continuation of the cranial 

 wall, but in front of the cranial cavity. 



For the rest, the quadrate region and its condyle (7.), the mandibles (fig. 7, ml-) and 

 the lower labials [LI.) have merely increased in size since the last stage. The same may 

 be said of the fronto-parietals {f.}^.) ; they are a little straighter, however. But the 

 parasphenoid (fig. 6, ^Jrt.5.) has been transformed into the normal shape, or nearly ; the 

 notch is now relatively much smaller : its shaft is long and wide also ; the basi-temporal 

 wings are now developed, they are pointed, raggedly lobate, and meet in a triangular 

 " handle." 



1 9 (continued). — (C) Cystlgnathus ocdlatas var. — Adult male ; b\ inches long. Dominica. 



This large sub-typical Frog has a skull (Plate IG, figs. 1-5), whose length is to its 

 breadth as 7 to 8 ^ ; it is a very regular half-oval in outline, and the condyles for the 

 lower jaw reach, very nearly, as far back as those for the atlas. Being of great 

 breadth, the auditory regions are extended like outspread arms, the parotic jjrocesses 

 being as wide as the capsules proper, outside the horizontal canals. 



The extent of the ossification of the endocranium is normally Ranine, and there 

 is clear tract of cartilage above and below the foramen magnum {f.m.), and the 

 ex-occipitals and prootics [e.o., pr.o) are distinct. 



The occipital condyles {oc.c.) are large, reniform, postero-inferior, and separated l)y a 

 space less than their own size ; the occipital arch itself is of great width, and well 

 marked oif from the auditory capsule, especially above. This is due to the great 

 size of the epiotic eminence {ep.), caused by the arch of the posterior canal ; this 

 eminence is unossified. So also is the outer half, below, and the outer third, above, 

 the prootic not reaching, even there, as far as to the squamosal {sq.). Thus the whole 

 of the extensive tegmen tympani {t-lij.) is unossified. 



Besides the high epiotic region another ichthyic character appears (seen to a less 

 degree in Rana pipiens, Plate 8), viz. : an extensive " pterotic " crest {pt.o.) ; this is a 

 backward and outward sigmoid process of the tegmen tympani, which doubles the 

 extent of the margin and overhangs the large annulus tympanicus (fig. 3, a.ty.), beliind. 



The prootics [pr.o.) reach as far as to the middle of the space between the 5th and 2nd 

 nerves (V., II.); the latter lie in a fenestra which reaches half-way from the prootic to 

 the girdle-bone [eth.). The interorbital region widens steadily from behind forward, it 

 is rather hollow above and below, for the side view (fig. 3) shows a concave outline 

 both to the roof-bones and the parasphenoid {f.})-, pa.s.). 



This enlargement forward is due rather to the growth of an " eave " over the fore part 

 of the orbit than to any great inci-ease in the size of the cranial trough within ; but for 

 that superorbital expansion the cranial trough Avould be seen as somewhat spindle- 

 shaped, bellying in the middle and narrower at either end. The outer edge of the 

 superorbital expansion is unossified, and in its fore edge the orbito-nasal nerve (fig. 3) 



