28 ILLINOIS BIOLOGICAL MONOGRAPHS [28 
and the verticale, the lamina medialis is pierced by two foramina, through 
the dorsal of which, the nasalis internus of the profundus nerve passes to 
the intermaxillary gland; while a blood vessel passes through the more 
ventral one. A small prenasal process extends anteriorly a short distance 
from the median ventral surface of the cupola. The internasal space is 
deep and narrow, and it is filled with intermaxillary glands which extend 
back beneath the planum basale, to its posterior margin. In the presence 
of these glands, Plethodon differs from Cryptobranchus and Spelerpes 
but resembles Amblystoma and Salamandra. 
In all essentials Plethodon resembles very closely the adult Amblystoma 
to which it is probably nearly related. The absence of earlier stages has 
prevented a study of the development of the capsule; but comparing the 
single larval stage of Winslow with my early stages of Amblystoma, 
coupled with the many resemblances between the adults, I am inclined to 
place Plethodon very near to Amblystoma. The absence of the fenestra 
infra-conchalis in Plethodon is the primary difference between these cap- 
sules; but the position and size of the planum verticale, the lamina externa 
and medialis, the anterior cupola as well as the large dorsal and ventral 
gaps are resemblances that suggest a very close relationship between these 
animals. 
NECTURUS MACULATUS 
As in Spelerpes, the chondrification of the nasal capsule of Necturus 
is greatly retarded; so that, except for the mere extension of the trabeculae 
into the head region, there is no evidence of a nasal skeleton up to the 25 
mm. stage. In higher Urodeles of this size, well developed capsules are 
already chondrified. 
In a 24 mm. larva, the trabecular crests are not developed, and the 
cylindrical trabeculae incline toward each other, but do not unite to form 
the planum basale. There is no evidence of a cornu at the anterior end, 
nor has the antorbital process yet chondrified; but procartilage cells have 
formed near the trabecula which indicate its later development. The 
forebrain lies lateral to the nasal sac and extends slightly anterior to the 
trabeculae. 
In a slightly older stage (Fig. 25), the anterior ends of the trabeculae 
more closely approach each other and near the tips they have expanded 
dorso-laterally, so that a cross section of the trabecula in this region is 
reniform. Miss Platt (1897) has described the independent chondrifica- 
tion of the planum basale, and its subsequent connection to the trabecula; 
although this stage does not show the chondrified basale, yet a few pro- 
cartilage cells lying in the tissue between the anterior ends of the trabeculae 
indicate its origin as independent of the trabeculae. In this stage also, a 
small triangular antorbital process has chondrified from the trabecula. 
