43] THE NASAL ORGAN IN AMPHIBIA—HIGGINS 43 
other. In Amblystoma, this process is.changed slightly, due to the 
independence of the ethmoidal columns from the cornua. In the 25 mm. 
larva, by medial growths of the columnae a pons has formed, so that in 
this stage the capsule is divided into dorsal and ventral halves, the only 
connection being the crista. By further chondrification of the region 
between the pons and the planum basale, a verticale is formed, the process 
continuing posteriorly, developing the solid thick cartilage of the 45 mm. 
larva. 
A planum verticale does not chondrify in Triton and Diemictylus, so 
that internasal space and cavity of the forebrain are separated by mem- 
branous structures only. The pons ethmoidalis develops in Triton, uniting 
the dorsal medial margins of the capsules somewhat anterior to the planum 
basale, but it is completely lost in Diemictylus. Evidence is lacking as to 
the origin of the pons in Triton, but Born (1876) describes the process as a 
continuous growth of cartilage from the trabeculae, and not as independent 
parts; it would appear, then, that the pons has probably arisen by growths 
from the medial surfaces of the capsules, similar to that of Salamandra. 
In the absence of a pons, Diemictylus appears to be reduced from some 
form like Triton; the nasal capsule of these two being very similar in other 
details. 
The antorbital process is present in all Urodeles, arising in all, except 
Cryptobranchus, from the ventral margin of the trabecula just back of the 
choana. It is directed laterally and anteriorly and in most Urodeles unites 
to the lamina externa, or to the cornu trabeculae, outlining the foramen 
orbito-nasalis, through which the nerves of the nasal region enter the 
capsule. In Necturus and Amphiuma, on the other hand, this process 
never unites to the more anterior parts of the capsule, so that a foramen 
is never formed, nor is there any posterior wall to the capsule as in those 
Urodeles where the antorbital unites to the tectale, as in Plethodon and 
Amblystoma. 
Gaupp (1893) held that the antorbital process of Urodeles is homologous 
with the pterygo-quadrate arch of the Anura; and the terms palatine 
cartilage or ethmo-palatine have been indiscriminately used when referring 
to this structure. If we regard Cryptobranchus as ancestral, or at least 
more primitive, a conclusion I believe both the nasal capsule and the 
olfactory organs justify, then the relations and the development of the 
antorbital process in this animal may throw some light upon the homology 
of these structures. In the two weeks larva, in which the trabecular 
crests are already well-developed, there is no evidence of an antorbital 
process; but slightly posterior to its probable position, procartilage cells 
lie near the lateral ventral margin of the trabecula, which continue pos- 
teriorly into the pterygoid process of the quadrate. In the later stage, 
these cells have chondrified and, uniting to the pterygoid, have reached 
