NERVOUS CENTRES. (Human Anatomy. Tue MEnrnces.) 
The cranial dura mater is not a simple bag. 
From its internal surface partition-like processes 
pass inwards, which serve to separate certain 
subdivisions of the encephalon. These are, 
the falx cerebri, the tentorium cerebelli, and the 
Jalz cerebelli. 
The falx cerebri is a process of fibrous mem- 
brane corresponding to the mesial plane and 
lying in the great median fissure of the brain, 
where it separates the lateral hemispheres from 
each other. Its shape is falciform ; its superior 
convex border corresponds to the frontal and 
Sagittal sutures, and encloses the great longitu- 
dinal sinus; its inferior border is concave and 
much shorter than the superior, and corres- 
ponds to the superior surface of the corpus 
callosum, which connects the hemispheres of 
the brain. In front the falx is very narrow and 
almost pointed ; it embraces the crista galli of 
the ethmoid bone, which appears to be enclosed 
between its layers. As the falx proceeds back- 
wards it increases considerably in depth; its 
Superior edge may be traced back to the internal 
Occipital protuberance ; its inferior edge termi- 
nates at a point corresponding to the middle 
line of the posterior margin of the corpus 
callosum. The falx cerebri contains within it, 
along its posterior border, a large vein, which 
is called the inferior longitudinal sinus. 
The falx cerebri is continuous at its posterior 
border on each side with the tentorium cere- 
belli. This process is nearly horizontal in its 
direction ; it forms a vaulted roof to a cavity 
the floor of which corresponds to the occipital 
) in which the cerebellum is lodged. Its 
upper surface is convex on each side of the 
attachment of the posterior extremity of the 
falx cerebri: it supports the posterior lobes of 
the brain. The inferior surface is adapted to 
the upper convex surfaces of the cerebellar 
hemispheres. Its posterior and outer edge 
adheres to the occipital bone and to the pos- 
terior border of the petrous portion of the 
temporal bone, reaching as far inwards as the 
osterior clinoid processes of the sella Turcica. 
@ occipital portion of this edge contains a 
considerable part of the lateral sinus (fig 362, e) 
and that portion which adheres to the petrous 
bone contains the superior petrosal sinus. The 
anterior or inner margin of the tentorium is 
concave and free in the greater part of its 
extent; it forms the posterior and lateral boun- 
dary of a large opening (which the sella Tur- 
cica completes in front), through which the 
crura cerebri and other parts connected with them 
pass. This margin is attached by its anterior 
extremities to the anterior clinoid processes, to 
reach which it crosses the posterior border. 
The crossing of these two edges at a point 
external to the sella Turcica gives rise to the 
formation of a little triangular space, the base 
of which corresponds to the sella Turcica; its 
outer angle is perforated for the transmission of 
the third pair of nerves, and its anterior one for 
that of the fourth pair. 
From the inferior surface of the tentorium 
cerebelli at its posterior edge, a short and thick 
fold of very slight depth descends to the pos- 
terior edge of the foramen magnum. This is 
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the falx cerebelli ; it corresponds to thé ned ian 
notch between the hemispheres of the cerebellum. 
Its anterior border is slightly concave. Two 
veins called occipital sinuses are contained in it. 
The internal surface of the cranial dura mater 
presents the same smooth appearance as we 
have noticed in the spinal membrane of the 
same name. We observe, however, an excep- 
tion to this on each side of the line along the 
great longitudinal sinus. Here it is very com- 
mon to find the membrane presenting a peculiar 
cribriform appearance, which occupies a space 
of from half an inch to two inches in length and 
not more than a quarter of an inch in breadth, 
but exhibiting great difference in various sub- 
jects as to the number and depth of the foramina 
or depressions upon which the sieve-like struc- 
ture depends. These depressions are caused 
by the presence of little bodies which grow 
from the layer of arachnoid that covers the 
brain, glandule Pacchioni, which will be 
described by-and-bye. The anatomist may 
expect to find in a large proportion of adult 
brains a greater or less degree of adhesion 
between these parts of the dura mater and the 
edges of the hemispheres of the brain. 
The dura mater is perforated by numerous 
orifices fur the transmission of the encephalic 
nerves. It adheres firmly to the border of each 
of the foramina in the cranial bones, and is 
partly continued in the shape of neurilemma 
over the nerve that escapes through it. In the 
case of the optic nerve a strong fibrous sheath 
is prolonged from the dura mater, and at the 
same time that membrane appears to become 
continuous with the periosteum of the orbit, as 
if it had, opposite the optic foramen, split into 
two layers, one of which formed the sheath of 
the optic nerve, and the other applied itself to 
the interior of the orbit, forming a periosteum 
to the walls of that cavity. 
Of the arteries and veins of the dura mater. 
—tThe disposition of the bloodvessels of the 
dura mater, both of the spine and of the cra- 
nium, deserves a special description. The 
former membrane derives its arteries from the 
numerous vessels which take their rise close to 
the spinal column in its various regions. These 
are ramifications of the abdominal and thoracic 
aorta or of their large primary branches. In the 
neck the deep cervical, the occipital, and the 
vertebral arteries send in numerous branches, in 
the back the intercostal arteries, and in the loins 
the lumbar arteries. These vessels pass in at 
the vertebral foramina, and send branches to 
the spinal membranes as well as to the bones 
themselves. 
The blood which is returned from the spinal 
cord and its membranes, as well as from the 
vertebra, is poured into a very intricate plexus 
of veins which surrounds the dura mater on 
its lateral and posterior surfaces, ramifying 
among the iohites of soft fat by which the 
exterior of that membrane is invested. This 
plexus is less ‘intricate in the dorsal than in 
the cervical or lumbar regions; it communi- 
cates very freely with the plexus of veins which 
lies on the exterior of the vertebral laminz and 
processes (the dorsi-spinal veins of Dupuytren). 
