OF THE SKULL IN THE UKODELOUS AMPHIBIA. 
585 
In neither is there any roof or floor cartilage, save below, in the trabecular rods them- 
selves ; the nasal region is not chondrified*; the auditory capsules are cartilaginous below 
and at their sides, but membranous above. 
For the rest the divergence is extreme ; in the Axolotl almost half each trabecula is 
parachordal, and the prochordal part does not reach to the nasal sacs, and only encloses 
the sides of the great pituitary fontanelle ; each trabecula is sending up an alisphenoidal 
crest. 
In the Frog or Toad the trabeculae have only a small parachordal tract ; they are 
long, grow beyond the pituitary fontanelle as a pair of diverging, but short cornua, but 
do not quite meet in front of the subcerebral fontanelle. 
In the Axolotl the suspensorium is a solid cartilage, growing forwards and outwards ; 
it has three upper processes, all distinct as yet from the trabecula ; these are the pedicle 
and its ascending fork, and the otic process ; there is no quadrato-pterygoid process for 
some weeks to come. 
The suspensorium is about two fifths the length of the free mandible, which meets its 
fellow in front of and under the upper part of the face. 
In the Batrachian the suspensorium is of the same size, or nearly, as the trabecula ; its 
apex or pedicle is a simple band of cartilage, which has already fused with the elbow of 
the trabecula behind, and its distal part is continuous with the ethmoidal region in front. 
There is no ascending and, for some weeks to come, no otic process ; the bar is narrow 
like the trabecula, runs parallel with it to the nasal region, and the two are, as we have 
seen, twice conjugated, like the filaments of Zygcena. 
Instead of being much longer than its pier, the mandible is one fourth the length 
only ; and like the “ horns ” of the trabeculae, these two bars are quite in the front of the 
head ; they cross under the fore face, like folded arms, and are evidently, for a long 
while, non-functional, the labials being, as in the Lamprey, the working jaws. 
In both there is no epihyal segment, or pier, to the hyoid arch ; when it does 
appear in the Batrachian, after two months or more, it comes with new credentials, and 
on another mission, than as a support to the arch of the tongue : in the Axolotl, and 
most of the Urodeles, it is entirely suppressed. 
But the cerato-hyal or free hyoid cornu is large in both ; in position and relation 
that of the Axolotl agrees now with that of an almost transformed Tadpole, being under 
the ear-sacs and attached to the back of a short suspensorium, and having a tape-like form. 
In the Frog and Toad it is a short, massive, obliquely 4-sided and 4-angled plate, 
whose attachment to the back of the suspensorium is in front of the eye. 
In the Axolotl the four flat branchial arches are all distinct, and the two foremost 
are composed of two pieces ; there are two basibranchials, and the last arch has no gills. 
In the Frog and its congeners the four gill-arches are all functional, and are all con- 
joined together above and below ; this series of pouched cartilages is conjugated by a 
single basibranchial. 
In the Urodeles they are formed on the same plan as in Selachians, Ganoids, and 
MDCCCLXXVII. 4 s 
