434 Julia B. Platt 
The antorbital processes have chondrified, and a large part of 
the cartilaginous skull is now incased in bone. The optic and 
oculomotor nerves pass outwards through two openings in the crista 
trabeculae as in the younger embryo, and the ramus ophthal- 
micus profundus trigemini extends forwards between the ascend- 
ing process of the quadrate and the trabecula, its union with the 
trigeminal ganglion being roofed by the fusion of the ascending 
process with the dorsal bar of the crista trabeculae (fig. 16). In 
the older embryo, however, a cartilaginous process extends backwards 
from the ascending process and fuses with the anterior wall of the 
auditory capsule. This process continues the line of the dorsal bar 
of the crista trabeculae, so that it now appears that the trige- 
minus, like the opticus and oculomotorius, passes outwards 
through an opening between the dorsal and ventral bars of the 
crista. The trigeminal ganglion lies between the quadrate and 
the auditory capsule, and from the ganglion the mandibular nerve 
passes outwards external to the ascending process, while the pro- 
fundus passes forwards median to this process. 
With the completion of the median wall of the otic capsule, 
the large opening found in the younger embryo (fig. 16) has become 
reduced to four smaller foramina, three of which le immediately 
above the floor of the capsule, while the fourth opening is found 
near the roof of the capsule, vertically above the cartilaginous par- 
tition separating the median of the three lower openings from the 
posterior. The dorsal foramen admits the ductus endolympha- 
ticus. The anterior of the three lower openings admits the facial 
nerve with the anterior of the two auditory nerves. The median 
foramen admits the posterior auditory nerve, while the posterior 
opening is the foramen perilymphaticum. 
It is thus seen that in the older embryo a cartilaginous partition 
separates the two auditory nerves. At the same time a ledge of carti- 
lage which grows inwards from the ventral part of the antero- 
lateral wall of the capsule forms a secondary floor separating the 
hyomandibular part of the facial ganglion from the auditory chamber. 
Through an opening left in this inner floor, the anterior auditory 
nerve, which has entered the posterior wall of the capsule with the 
facial nerve, passes upwards to the sensory membrane, while the 
rami hyomandibularis and palatinus pass through the lower 
and primary floor of the auditory capsule by their respective fora- 
mina. As in the younger embryo, the glossopharyngeal and vagus 
