454 NERVOUS SYSTEM AND SENSE ORGANS OF AMIURUS. 
PLATE VI.—(Continued). 
the dura mater medullaris. Between these two membranes is 
the characteristic loose adipose tissue. The roof of the neural 
canal is here formed by cartilage which has largely undergone 
ossification both from the centre and the perichondrium. It is 
invested on the outside by the membrane bone in continuity 
with the third spinous process. The dorsal musculature lies 
above the anterior part of the tranverse process of the fourth 
vertebra and the saccus paravertebralis which contains the mal- 
leus. (Vide Fig. 4). 
Fig. 2.—Through the ventral roots of the second nerve (further back than the 
dorsal) (vide Fig. 8, Pl. IV.) which emerge behind the ascending 
processes of the stapes (right side is somewhat further back- 
wards). Between the neural arches of the first vertebra is the 
thickened patch of dura mater which furnishes the membranous 
wall of the neural canai as well as the dura mater medullaris. 
Fra. 3.—Shows the dorsal roots of the second spinal nerve emerging above 
the ascending processes of the stapes. The neural arches of the 
first vertebra are seen as the articular processes of the stapes. 
The ventral roots of the second are seen in a canal of dura mater 
in their backward course towards their foramina. The anterior 
spoon-shaped process of the stapes is caught just behind the 
atrium sinus Imparis. 
Fia. ‘4—Is through the middle of the atria sinus imparis, the partition be- 
tween which is formed by the thickened dura mater which is in 
continuity with the connective tissue surrounding the stapes, 
and that on the outside of the claustra. The separation of the 
layers of dura mater is less complete, but in the dorsal part of 
the spinal canal the medullary can be distinguished from the 
vertebral layers and between them the rest of the membrane is 
continuous with the loose adipose tissue. The tips of the claus- 
tra project slightly from above into the atria sinus imparis. The 
whole of the saccus paravertebralis containing the oily reticular 
tissue is seen in section, the malleus and incus being connected 
to the stapes by tendon. 
Fig. 5.—The basi-occipital is here only exposed for a small portion in the 
middle line owing to tlie ex-occipitals abutting on it. The section 
passes through the communication between the cavum and atria 
sinus imparis, the partition (dm. of last figure) being only 
caught above. The atria open above into the reservoir (rst). 
The lateral wall of the neural canal is formed by the connective 
tissue separating the claustra from the ex-occipitals. 
Fig. 6.—The reservoir appears in this section, which passes through the 
foramen magnum, slightly bilobed. ‘The dorsal and the ventral 
roots of the first nerve are caught in the bony canal through 
which they emerge. The cavum sinus imparis is cut behind the 
saccus endolymphaticus. It contains only fluid like the atria 
- and reservoir, no reticular tissue. The posterior surface of the 
lagena cochlex is just caught. The osseous roof of the cavum 
thins out before it joins the patch of dura mater. 
Fic. 7.—Just behind the vagus foramen, and through the strong ventral roots 
of the first spinal nerve, the membranes of the brain have here 
the features characteristic of the cranial cavity. The osseous 
roof of the cavum sinus imparis is somewhat thicker, its walls 
much thinner. It contains here the thin walled saccus endolym- 
phaticus. In the foveae sacculi is the section of the pars inferior 
