DURA MATER. 5d7 
~ blood from veins which come from various parts of the brain. They are described 
in the section dealing with the Vascular System. 
| Strong fibrous partitions or septa are given off along certain lines from the deep 
Ty 
ra 
: . f a 
Cavernous sinus 
\ Y, 
Internal carotid artery \ \ 
/ NA 
Basilar sinus AN \ Superior petrosal sinus 
/ fe 
/ f MENS 
Inferior petrosal sinus Lateral sinus 
Fic. 413.—SaciTraL SECTION THROUGH THE SKULL, A LITTLE TO THE LEFT OF THE MESIAL PLANE, 
to show the arrangement of the dura mater. 
The cranial nerves are indicated by numerals. 
surface of the dura mater. These project into the cranial cavity, and subdivide it 
partially into compartments which all freely communicate with each other, and 
each of which contains a definite subdivision of the brain. These septa are: (1) the 
falx cerebri; (2) the tentorium cerebelli; (3) the falx cerebelli; and (4) the 
diaphragma selle. 
The falx cerebri is a sickle-shaped partition which descends in the great longi- 
tudinal fissure between the two hemispheres of the cerebrum. In front it is narrow, 
and attached to the crista galli of the ethmoid bone. As it is followed backwards 
it increases in breadth, and behind, it is attached along the mesial plane to the 
upper surface of the tentorium. The anterior narrow part of the falx is frequently 
cribriform, and is sometimes perforated by apertures to sueh an extent that it almost 
resembles lace-work. Along each border it splits into two layers, so as to enclose a 
blood sinus. Along its upper convex attached border runs the great longitudinal 
sinus ; along its concave free border courses the much smaller inferior longitudinal 
sinus ; whilst along its attachment to the tentorium is enclosed the straight sinus. 
The tentorium cerebelli is a large crescentic partition of dura mater, which forms 
a membranous tent-like roof for the posterior cranial fossa, and thus intervenes 
between the posterior portions of the cerebral hemispheres and the cerebellum. It 
is accurately applied to the upper surface of the cerebellum. Thus its highest point 
is in front and in the mesial plane, and from this it slopes downwards towards its 
attached border. It is kept at a high degree of tension, and this depends on the 
integrity of the falx cerebri, which is attached to its upper aspect in the mesial 
plane. 
The posterior border of the tentorium is convex, and is attached to the hori- 
