61) THE NASAL ORGAN IN AMPHIBIA—HIGGINS 61 
are well exemplified in Necturus where, even in the adult, the capsule is 
more nearly entire than in any other genus; a condition which may be 
explained on the supposition that Necturus is to be regarded, not as more 
primitive than other Urodelan genera, but as a permanent larva, a view 
which has been advocated by many in recent years. 
In Amblystoma, as detailed in the foregoing pages, this history is 
carried farther. There is first a progressive development tending toward 
a complete capsule, but never approaching completeness as nearly as does 
the adult Necturus. Then, in conjunction with the process of meta- 
morphosis, there comes a resorption of parts and a modification of those 
that persist, resulting in large vacuities in both floor and roof of the cap- 
sule. These steps are detailed above, and the final result is an envelope 
for the olfactory organ in which parts are recognizable as homologous 
with those of the capsules of the adult Anura. 
In the history of the capsules in all Amphibia the following parts are 
concerned. The two trabeculae are united in the ‘ethmoid’ region by what 
Gaupp and others have called an internasal plate. This lies below the 
tip of the brain and is the ‘ethmoid plate’ of Winslow or the ‘planum 
basale’ of the foregoing description. In front of this planum basale, the 
trabeculae continue as the cornua trabeculorum to the tip of the skull, 
supporting the anterior part of the nasal organ. In several Urodeles, 
where I have studied the early larval stages (this history has not been 
followed in the Anura with sufficient detail to say whether it holds for them) 
a bar of cartilage, the columna ethmoidalis, arises on the upper medial side 
of the olfactory organ (either independently or as an outgrowth from the 
cornu) and lies parallel to the lower trabecula. By a lateral growth from 
this ethmoidal column, the planum tectale extends over the dorsal surface 
of the nasal sac, uniting in the later stages to the cornu trabeculae. The 
term lamina cribosa, used by Winslow (1898) and Terry (1906) to designate 
this cartilage is a misnomer, for it is hardly necessary to say that it cannot 
be homologous with the structure bearing the same name in the mammals, 
as it lies wholly dorsal to the olfactory nerve. 
In the larvae of several Urodeles, and in my single larva of Rana, the 
ethmoidal columns of the two sides are connected by a pons ethmoidalis 
which roofs the fenestra ethmoidalis leading from the cavum cranii to the 
ethmoid region. This is only a temporary condition in most amphibia 
where the chondrification of the planum verticale closes the fenestra and 
unites the floor and roof of the capsule. In Triton and Diemictylus, on 
the other hand, the planum verticale never develops; so that cavum cranii 
and internasal space are separated by membranous structures only. 
The last special element entering into the formation of the capsule is 
the antorbital process, which needs a somewhat longer discussion. In 
the Urodeles, a process arises from the side of the trabecula just back of 
