DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
105 
24 (continued).—(B) Camariolius tasmaniensis (?).—Larva, f inch (9 lines) long ; legs, 
3 ^- inch. Same locality. 
This Tadpole was the largest of several of this species examined by me, and its free 
hind legs showed that it has attained to its full larval condition; it was as long with 
its tail as its parent without. 
In the possession of paired nasal sacs, each with a distinct roof, and of a well defined 
fenestra ovalis, this larva had gone beyond the Lamprey; hut there was no bony 
deposit even below the skull (parasphenoid), and the hinder half of the long hypo¬ 
physial space was still membranous ; the rest of the space was composed of a very 
thin layer of young, half consistent cartilage. 
This skull, therefore, was in the best possible state for comparison with that of 
Petromyzon and its allies. 
Leaving out the prenasal structures this skull (Plate 15, figs. 6, 7) is nearly square; 
it is unusually short, and although the head was no larger than that of a Blow-jly, the 
chondrocranium had become a very solid structure; and cartilage was forming even in 
Tadpoles one-third the length of this—that is, in newly-hatched specimens corres¬ 
ponding to my earliest stage in Bufo vulgaris (Phil. Trans. 1876, Plate 55, fig. 1). The 
first-formed cartilage can now be well seen, as it is much more massive, and richer 
with proliferating cells, than the newer tracts. 
The cartilage, which at first only enclosed the apex of the notochord as the ends of the 
trabeculae, has now spread along the whole hind floor and a very definite tract crosses in 
front of the notochord. That rod is expanding to its full (spinal) size just where it 
emerges from between the parachordal bands (iv. ); they pass outwards and backwards, and 
end in a free rounded point behind the ganglion of the 9th and 10th nerves (IX., X.), 
which lies in a notch in the outer border of each band. These bands are distinct 
until they reach the apex of the notochord, and then, as just mentioned, unite in front 
of it; there they form the hinder boundary of the pituitary space. Directly in front 
of the notch for the ganglion each parachordal dilates suddenly into a broad crescentic 
wing, which forms a concave floor for the antero-internal half of the auditory capsule 
(fig. 7) right and left. There is a shallow crescentic notch in the middle of the hinder 
margin of each wing; this forms the inner boundary of the fenestra ovalis ( f.o .). In 
front, there is a deep round notch between the wing and the trabeculae; in and over 
this space lie the more or less united ganglia of the 5th and 7th nerves (V., VII.). 
The sub-orbital fenestra, and the band of cartilage which encloses it are, together, 
scarcely of larger extent than the auditory capsules behind. These have lost their 
simple oval form, for-the three large canals and their globular ampullae (i a.s.ch.s.c., 
p.s.c.) above, and the sacculus (■ vb .) below, have wrought the sac into their own form. 
The alate basal floor is thin, and composed of rather young cartilage, but the 
auditory sacs are very solid, for they become cartilaginous directly after hatching, 
coevally with the trabeculae and suspensoria. 
MDCCCLXXXI. 
p 
