DEVELOPMENT OP THE SKULL IN THE BATRACHIA. 161 
the Nearctic and Neotropic regions, that the Indian “ Polypedatidse ” do to the typical 
Frogs of their own region. 
In general development the skull is about equal to that of Polypedates maculatus 
and chloronotus (Plates 27 and 26), but the ear-organs are more arrested ; altogether, 
however, it is a lighter and more elegant skull, and is almost exactly intermediate 
between the skull of a Cystignathus (of the same size), on one hand, and that of such a 
true Ilyla as H. rubra (Neotropical), (Plate 33, figs. 6, 7) on the other. I shall com¬ 
pare it with that of Cystignathus ocellatus and typhonius (Plate 16). 
The length is nine-tenths of the greatest breadth (Plate 29, figs. 7, 8), and the cheeks 
rapidly narrow in towards the broad, rounded snout. 
The fore and middle regions are of equal axial length ; the hind skull is only 
two-thirds their length, but it is of great breadth; the ossification, outer and inner, is 
typical; the whole structure is elegantly light, but of considerable strength. The 
occipital condyles ( oc.c .) are small, project but little, are directly posterior, and are nearly 
twice their own breadth apart; they are separated by a gently emarginate line ; the 
condyles for the mandibles reach as far back as the fore edge of the stapes. The upper 
and lower median cartilaginous tracts are rather wide, and the superoccipital edge 
(fig. is almost as far back as the basioccipital. The prootics and ex-occipitals 
( pr.o ., e.o.) of the same side are continuous, and the bone reaches in front to the optic 
fenestra (II). 
The bone, outside, reaches beyond the horizontal canal ( h.s.c .) and then there is a 
large lozenge-shaped tract of cartilage which ends in the tegmen tympani ( t.tiy .), whose 
margin stretches outwards and forwards. 
In front of the ampullae of the anterior and horizontal canals (ci.s.c., h.s.c.) there 
is a blunt hook of bone, looking outwards ; this process is also developed largely in 
Siren lacertina (Huxley, Art. “Amphibia,” Encyc. Brit., 9th edit., p. 758; and 
Wiedersheim, “ Das Kopfskelet der Urodelen,” plate 1, figs. 11, 12, Y. F., and 
plate 2, fig. 18, Y. F.). I have worked out this part in Siren, and in the correspond¬ 
ing stage in the larvae of Triton cristatus, and I find it to be a foregrowth of the plaster 
of cartilage developed beneath more or less of the auditory capsule—an outgrowth 
from the bevelled edge of the basal plate, or “ investing mass.” 
The hinder roof (tegmen cranii) reaches to the optic fenestrse ; it has two lesser 
fontanelles in it. The main fontanelle is a long oval, half the extent of the roof. 
The fontanelle is narrow because the tegminal edges are wide, equal to the scanty 
tegmen in front—the top of the girdle-bone ( eth .); there is a small open space there, 
and a lozenge-shaped naked tract of the ethmoid. The temporal fossse are large and 
round, being margined outside by the prootic spurs ; then the rather narrow skull 
steadily widens forwards, as in Cystignathus ocellatus (Plate 16, figs. 1, 2). 
Infero-laterally, two-fifths of the mid skull is unossified, the large optic fenestrse 
lying at the end of the soft tract, right and left. 
In this flattish skull the girdle-bone barely reaches the true nasal region, and does 
MDCCCLXXXT. Y 
