DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
19 
Skulls of larval “ Ranidas.” 
Chondrocranium of perfect larva of Bull Frogs. 
First Stage. —1. Tadpole of Ran a clamata (A), whose total length was 3^ inches; of 
the tail, 2 inches; and of the hind legs, 5 lines (- x - 2 - inch). 
The skull (Plate 2, figs. 5, 6) lias now attained its full cartilaginous ( Petromyzine) 
condition, and has gone beyond it; there is a pair of cartilage-bones, and there are 
three membrane bones. I shall deal with these signs of metamorphic progress after 
describing the chondrocranium. 
The cranium, proper, is now a small flat-bottomed boat, with a semi-cartilaginous 
deck; this has been constructed upon the original frame in the following manner. 
The large open space in the orbital region has acquired a thin floor of cartilage, and 
this median (“ intertrabecular ”) tract has grown forwards to the region of the inner 
nostrils ( i.n .), where the trabeculae have grown together, and are diverging again as 
free, flat, broad-ended “cornua” ( c.tr.). 
Behind, the occipital arch is as perfect as may be, for the auditory capsules (vb.) 
fit into large fenestras in its sides; its top ( s.o .) is flat, and extends to the fore¬ 
most third of the capsules ; its floor is flat, and contains the diminishing notochord (nc.) 
in its middle : in this kind this rod scarcely acquires any true cartilage in its outer 
sheath. 
In the large orbital region the side walls are cartilaginous, except where the optic 
nerves (II.) pass out of their “ fenestrae ”—spaces three or four times as large as the 
actual foramina. 
As in the occipital region, so also in this, there is a cartilaginous “tegmen;” its 
halves have not united in the middle, and a bilobate “ fontanelle ” (fo'.) exists between 
these growths and the superoccipital cartilage. Then there is a large oval fontanelle (fo.) 
or membranous space up to a short distance of the end of the cranial cavity, where a 
tract of cartilaginous roof margins this egg-shaped space. 
Here there is a perfect cartilaginous cincture, which becomes in the adult the “ os 
en ceintureits front end is extended as a cartilaginous beak formed from below 
upwards as a crested tract of the “ intertrabecula this is the mesethmoicl ( p.e .) in 
rudiment; the lateral regions are the right and left “ ecto-ethmoids” (al.e.). 
These lateral parts grow outward into wings whose scooped front margins form a 
back wall to the nasal sacs ; the olfactory nerves pass to these sacs through “ fenestras ” 
that lie between the middle and outer parts of the cincture. 
The nasal roofs are still soft, and in the dissection the olfactory sacs were removed 
to display the cartilages. 
But the interna] nostrils (i.n.) are shown in these figures ; they are large and 
neatly circular ; much of their margin is seen to be formed by the narrow, clinging 
part of the trabeculae, and the curved spat idee that grow out from the ethmoidal 
P ‘2 
