DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
229 
make it normal; it is large, well developed, and has a spatulate extra- and a lignlate, 
fixed, supra-stapedial (e.st., s.st.), 
The stylo-hyal ( st.h .) is confluent; it is not enlarged above, as in the other kind ; 
the rest of the bar (fig. 4, c.hy., h.hy.) is narrow, without a lobe. 
The lateral lobes of the basal plate ( b.h.br .) are well developed, the notch in front 
and the main plate are of the average size, and the thyro-liyals ( t.liy .) are long, and 
moderately divergent. Between them there is a thick, ossified mass, with a free 
rounded fore margin ; this is the last basi-brancliial ( b.br.) ; its hinder margin is grooved. 
In front of this bony ridge the plate is keeled, below, and this keel expands behind 
the front notch into a triangular mass, the first basi-brancliial; the whole keel is more 
or less calcified. 
The three characteristic hyo-branchial plates of this and the two other kinds 
(Plate 43, figs. 4, 6, and 10,— Engystoma) evidently belong to three closely related 
species. 
In the main skull (Plate 43, figs. 1, 2) the investing bones are as feeble as the 
centres in the chondrocranium. The fronto-parietals (fig. \,f.p.), thin shells pointed 
in front, dilated postero-externally, and nowhere meeting at the mid-line, exactly 
correspond to their counterparts in metamorphosing Common Tadpoles. So also 
the broadly-crescentic nasals (n.) with their facial handle, and the frail marginal 
bones (px ., nix., qfi), and, running along the suspensorium, the squamosal (sq.). The 
parasphenoid (fig. 2, pa.s.) has its basi-temporal wings larger than it cochleariform 
rostrum ; the hind part is a large triangle. 
The small ragged vomers (v.) have all the four normal processes, in size and develop¬ 
ment they come between those of this and the next kind; they protect the inner edge 
of the rather small, round, inner nostrils ( i.n .), which like the outer (e.n.) are extremely 
wide apart. 
In some things this skull comes nearer the “ norma ” than the two last, viz.: in its 
perfect annulus, well-developed columella, and distinct prootics and ex-occipitals. It 
is farther from it in the extreme feebleness of all the bony tracts in the main skull, 
and in the total absence of the girdle-bone ; also in the retention of the “ orbitar 
processthe clear regional mark between the post-palatine and pterygoid cartilaginous 
tract; in the more perfect development of the thick, bony, uncinate last basi-brancliial ; 
and especially in having a rudiment of both a supra- and a basioccipital. 
These minute forms are well worthy of study in their irregular, and as it were, 
halting metamorphosis ; and this is to be noted, namely, that generic groups may be 
made according to the taste of each individual Zoologist; no two species agree in all 
things, and in some existing genera each species might be put by itself, and have its 
own generic, as well as specific, name. 
