494 Julia B. Platt 
but in its backward growth soon meets the side of the chorda near 
the transverse plane passing through the middle of the auditory 
vesicles. Anterior to this plane, the median prochondral tissue of 
the basieranial plate disappears, and the chorda extends free nearly 
to the posterior wall of the hypophysis. In Triton, according to 
STÖHR (80), the trabecular plates meet at each side the point of 
the chorda, which they soon surround anteriorly, occupying thus that 
area of the basicranial plate which in Necturus does not chondrify. 
In the Anura (STOHR’82), although the trabecular plates ultimately 
surround the point of the chorda, at first the chorda extends forwards 
completely free beyond the region in which its sides are enclosed 
by the trabecular plates, as is permanently the case in Necturus. 
This condition in Necturus, however, is evidently secondary, as 
evinced by the disappearance of the antero-median part of the basi- 
cranial plate. 
Fig. 14, pl. XVIII, is a diagram showing the early relations of 
these tissues. The procartilage of the basicranial plate is bounded . 
posteriorly by the line —d and terminates anteriorly in two horns 
that reach as far forwards as the optic stalks, or to the line a—a, 
where they pass into the mesectodermic part of the trabeculae, 
indicated in the diagram by dotted outlines. Although the trabecular 
bars are here represented as lying in the plane of the basicranial 
plate, in reality they curve downwards as seen from the sagittal 
section shown in fig. 10, pl. XVIII, or from the model shown in 
fig. 7. 
The position of the membranous ear is indicated in the dia- 
gram, and two short cross-lined bars extending on the right from 
the basicranial plate towards the auditory vesicle show the position 
of the first two fusions taking place between the cartilage of the 
ear, and the basal plate. In the embryo of 17 mm, the tissue about 
the ear is still unchondrified. The connection between the auditory 
capsule and basal plate occurs in the embryo of 18 mm, when the 
anterior, posterior, lateral, and ventral walls of the capsule (save 
the foramina) are chondrified, but while the median and dorsal 
walls of the capsule are still open. The anterior of the two connec- 
ting bars forms first. It lies immediately posterior to the egress 
of the ramus hyomandibularis facialis from the facial ganglion, 
former »basicranial«, the latter »basal«e.. The two plates are not coextensive, 
and consequently do not represent the same plate in successive stages of car- 
tilaginous development. 
