20 ILLINOIS BIOLOGICAL MONOGRAPHS (20 
the olfactory organ; and together with the posterior prolongation of the 
cornu form a shelf upon which the posterior parts of Jacobson’s organ rest. 
Slightly anterior to its junction with the cornu, the tectalesis pierced by a 
small circular foramen, which, like the infra-conchalis of Amblystoma and 
Triton, contains the anterior end of the organ of Jacobson. The planum 
tectale is interrupted on its anterior half by two oval openings, of which the 
external naris is the larger, extending back nearly to the middle of the cap- 
sule. The more medial gap is much smaller and marks the beginning of the 
process of resorption, just as in the older Triton larva. 
The lamina medialis (/m) is continuous with the tectale and forms the 
medial wall of the capsule from the planum basale to the anterior cupola; 
while ventrally, it curves into the floor of the capsule which is pierced by 
two small foramina, through which rami of the nasalis internus nerve 
leave the capsule. The main branch of this nerve passes to the internasal 
space through the larger foramen just in front of the base of the pre-nasal 
process. 
The adult Diemictylus (Fig. 15) shows no further chondrification of 
structures than those present in the larva. Ossification has taken place in 
all parts and further resorption has increased the size of the gaps present 
in the earlier stage. A single foramen exists above the antorbital process, 
so that both nasalis internus and externus of the profundus nerve enter the 
capsule through the foramen orbito-nasalis. 
The planum tectale is more vaulted than before, and its posterior half 
is pierced by two foramina; the medial of which is for a branch of the pro- 
fundus nerve, while the lateral and larger one contains, as before, the 
cephalic end of Jacobson’s organ. The anterior tectale has two large 
openings, the external naris, lateral in position, and, medial to this, the 
further development of the gap begun by resorptive processes of the larva. 
The ventral surface of the adult capsule has a greatly enlarged choana, 
which occupies the posterior two-thirds of the floor. It is bounded laterally 
by the prolongation of the cornu, which in this stage extends beyond the 
junction to the tectale, so that a short process, behind the shelf, supports 
the posterior parts of the organ of Jacobson. The anterior part of the floor 
and the cupola need no description, further than the mention of five small 
foramina for branches of the nasalis internus nerve. 
The nasal capsules of Triton and Diemictylus are very close. The 
presence of the same large gaps, and the reduced planum basale, together 
with the continuity of cavum cranii with the internasal space are strong 
resemblances between the two. The fenestra ethmoidalis is not a perma- 
nent character of any other adult, although it is temporary in some larvae 
as Salamandra and certain Anura. There are some resemblances between 
the capsules of the adult Amblystoma and Diemictylus. In both, the 
anterior part of the organ of Jacobson extends through a foramen which in 
