202 
MR. W. K. PARKER ON THE STRUCTURE AND 
segmented off, and is also very narrow; it soon dilates into a sub-orbicular convex 
extra-stapedial ( e.st .), which gives off a supra-stapedial band (s.st.) that is confluent 
above. 
The labials (u.P.u.l 2 .), septo-maxillaries ( s.mx .), and the marginal bones ( px ., mx., q.j.) 
are all like those of the last kind, but smoother and less solid in this young spec im en. 
The ear-shaped top of the squamosal (sq.) does not reach the roof-bones, and is less 
broad in its postorbital region. The roof-bones ( f.p .) are already anchylosed to the 
endocranium behind ; the fronto-nasal suture is more triangular. The cerato-hyal 
(Plate 38, fig. 6, c.hy.) is broad in the middle without any sudden enlargement; the 
basal plate (b.h.br.) is narrower than in the last kind; the anterior lobes are broader, 
and the right hind lobe is ear-shaped also. 
The differences here noticed are partly due to age, but some of the modifications 
would be found in the skull of an old individual; it is more Ranine, having a separate 
inter-stapedial piece. 
57. Bufo aqua.— Old female, 6^ inches; young do., 5 inches long. South America. 
This large kind has a skull which is the Bufonine counterpart of that of the Bull¬ 
frog (Rana pipiens) ; they are the largest of the Order, or have scarcely any rivals, and 
in both the skull has much that is archaic or generalised. In the great Frog the skull 
is smooth and neat, and very narrow in the interorbital region (Plate 8); here the 
roughness and strength, and the breadth of the mid skull, are all exaggerated : the 
one is a caricature, so to speak, of a Frog’s skull, and the other of a Toad’s. 
In this (Plate 36), as in the last, the length is only three-fourths of the breadth ; 
here the condyles of the quadrate go as far back as the root of the occipital condyles, 
but they fall short, very much, of what is seen in the larger Frogs. 
The ossification of the endocranium is much greater than what we have seen in 
the Ethiopian B. pantherinus; and here, with no pretence to the sub-Ganoid condition 
such as is seen in some Frogs, the investing bones are very extensive, solid, and 
coarse. 
There is a great approach here to the triangular form in the general outline ; this 
will be seen still more in the species yet to be described; the hinder margin shows 
all the projections to be almost flush with an imaginary transverse line drawn across 
the skull behind; the occipital condyles project beyond, the quadrate condyles reach, 
and the epiotic eminences just come short of, such a line. The occipital condyles 
(oc.c.) are sub-oval, swpero-posterior, they are of moderate size, and are separated by a 
crescentic notch larger than themselves. The whole hind skull is one mass of hone 
up to the covered tegmen tympani; in a younger individual (fig. 4) this part is 
largely cartilaginous ; the ossification reaches in front to the optic fenestree (II.). Only 
one-fourth of the interorbital region is unossified, and only the front half of the nasal; 
the girdle-bone takes up all its own region and half of the nasal and orbito-sphenoidal. 
