DEVELOPMENT OP 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 {f.p) are less developed; each bone is a sharp style, growing 

 broader behind, and shell-like. 



Also the parasphenoid, below Cfig. 2, jxt.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. clamuta; the " tegnien 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 suspensoriura, 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 trabeculse is a 

 mere blunt projection. The jDalatine ridge ("post-palatine x\\d\mer\t" pt.pa.) 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 (mk.) are needed. Here the 

 condyle for the hyoid (fiy.f.) is only two-thirds the distance from the hinge for the 

 lower jaw, as compai-ed with the former instance. 



Except in Pseudis, to be aftei-wards described, there is no better kind of Tadpole 

 than tliis 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.Jiy.) 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 m Plate 3, fig. 3, articulating by a 

 somewhat convex condyle with the flattish facet imder the fore part of the suspeu- 

 sorium. 



Outwards and backwards from the joint the "stylo-hyal" process {st.Ji.) forms a 

 large irregular triangle ; below, the " hypo-hyal " 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 cartihige 

 with a rounded lobe growing from its hinder broad end : this is the 1st basi- 

 branchial with a rudiment of the 2nd [h.br.). 



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 commou 

 "hypo-branchial" plates {h.br.). 



