DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
23 
they are crescentic and enclose the outside of each “foramen ovale;” these are the 
prootics (V. pr.o.). 
The fronto-parietals (fp) are less developed; each bone is a sharp style, growing 
broader behind, and shell-like. 
Also the parasphenoid, below (fig. 2, pa.s.), is altogether a smaller bone, with more 
slender processes; in front it stops short obliquely: here there will appear an additional 
and rare centre—the “ pro-parasphenoid” (see fig. 5, pa.s'.). 
The auditory capsules are relatively less than in R. clamata; the “ tegmen tympani ” 
is a rounder, less pronounced growth, and the position of the stapes and its fenestra 
(st.) is more oblique and inferior in position. 
The narrow-waisted cranium, and the more out-turned suspensorium, make the 
subocular fenestra of a very regular oval shape instead of oblong. 
The orbitar processes ( or.p .) are smaller, and the quadrate region in front of them 
shorter; and the spur ( pr.pa .) which by ligament is tied to the cornu trabeculae is a 
mere blunt projection. The palatine ridge (“post-palatine rudiment,” ptpa.) projects 
backwards less, but is larger than the outer wing of the ethmoid ( al.e.). 
The arcuate form of these great suspensoria throws the quadrate condyles further 
(obliquely) inwards, and thus shorter free mandibles (mJc.) are needed. Here the 
condyle for the hyoid (hyf) is only two-thirds the distance from the hinge for the 
lower jaw, as compared with the former instance. 
Except in Pseudis, to be afterwards described, there is no better kind of Tadpole 
than this of the American Bull-frog for showing the structure of the post-oral 
arches. 
The figure (Plate 2, fig. 8 ) was taken from a dissection of a larva 3f inches long; 
it is drawn as it appeared from above, after the gill-tufts were cleared away, and the 
whole basket-work somewhat flattened out for display. 
The “cerato-hyals” ( c.liy .) are roughly hourglass shaped; very solid in the middle, 
and twisted ; they flatten out into massive slabs at each end. 
The natural position of those bars is shown in Plate 3, fig. 3, articulating by a 
somewhat convex condyle with the flattish facet under the fore part of the suspen¬ 
sorium. 
Outwards and backwards from the joint the “stylo-liyal” process (st.h.) forms a 
large irregular triangle ; below, the “ hypo-liyal ” region is greatly outspread or pedate. 
Each lobe projects inwards at it foremost third, and the right and left lobes are united 
by an isthmus of simple ( embryonic) cartilage—the “ basi-hyal ” tract ( h.hy.). 
Wedged in behind this band of arrested tissue we see a large oval azygous cartilage 
with a rounded lobe growing from its hinder broad end: this is the 1st basi- 
branchial with a rudiment of the 2nd ( b.hr.). 
Overlying this rudiment, and articulating with the main piece, there is a pair of 
winged cartilages, closely applied each to each at the mid-line : these are the common 
“hypo-branchial” plates ( h.br .). 
