These (Sinus duræ matris) are blood-spaces between the meningeal and
periosteal layers of the dura mater and are lined with endothelium. In
many places the lumen is crossed by fibrous strands. They receive the
veins of the brain, communicate with the meningeal and diploic veins,
and with veins outside of the cranium; their connections with the latter
are by means of small =emissary veins= (Emissaria). They convey the
blood directly or indirectly to the jugular veins. Some are paired,
others unpaired. They may be divided into dorsal and basilar systems.
The =dorsal system= comprises the following:
The =superior longitudinal= or =sagittal sinus= (S. sagittalis superior)
is situated in the upper border of the falx cerebri along the internal
sagittal crest. It begins at the crista galli and ends at the tentorium
osseum by dividing into two transverse sinuses. It receives the superior
cerebral veins. Along each side are small pouches (Lacunæ laterales)
into which the veins open. The lumen of the sinus is traversed by
fibrous bands and is partially divided by a longitudinal septum.
[Illustration:
FIG. 464.—MEDIAN SECTION OF HEAD OF HORSE, UPPER PART WITH SEPTUM NASI
REMOVED.
_a_, Lateral mass of ethmoid bone; _b_, superior turbinal; _c_,
inferior turbinal; _d_, _d′_, turbinal folds; _e_, frontal sinus;
_f_, falx cerebri; _g_, tentorium cerebelli; _h_, medial surface of
hemisphere; _i_, cerebellum; _k_, occipital bone; _k′_, occipital
condyle; _k″_, paramastoid process; _l_, external auditory meatus;
_m_, temporal condyle; _n_, parieto-temporal canal; _1_, branches of
ethmoidal artery; _2_, _2′_, branches of sphenopalatine artery; _3_,
_3′_, branches of sphenopalatine vein; _4_, branches of ethmoidal
nerve; _5_, _5′_, branches of sphenopalatine nerve; _6_, artery of
corpus callosum; _7_, superior sagittal sinus; _8_, straight sinus;
_9_, vena magna cerebri; _10_, inferior sagittal sinus; _11_, _11′_,
transverse sinuses; _12_, superior petrosal sinus; _13_, superior
occipital sinus; _14_, superior cerebral vein; _15_, corpus
callosum; _16_, fornix. (After Ellenberger, in Leisering’s Atlas.)
]
The =transverse sinuses= (S. transversi), right and left, pass outward
in the transverse grooves of the parietal bones, enter the
parieto-temporal canals, and are continued by the superior cerebral
veins to the superficial temporal veins. The two sinuses are connected
by the sinus communicans.
The =inferior longitudinal= or =sagittal sinus= (S. sagittalis inferior)
runs backward on the upper surface of the corpus callosum along the
concave edge of the falx cerebri and joins the great cerebral vein (of
Galen) to form the straight sinus.
The =straight sinus= (S. rectus) passes upward and backward between the
cerebral hemispheres and in the tentorium cerebelli and joins the
superior sagittal sinus. The point of meeting is the confluence of the
sinuses (Confluens sinuum).
The =occipital sinuses= (S. occipitales) lie on either side of the
vermis cerebelli. They empty anteriorly into the sinus communicans and
communicate behind with the spinal veins.
The =superior petrosal sinuses= (S. petrosi superiores) pass in the
tentorium cerebelli to end in the transverse sinuses.
The =basilar system= consists of the following:
The =cavernous sinuses= (S. cavernosi) lie in the inner grooves of the
root of the temporal wings of the sphenoid bone at either side of the
sella turcica. The two are connected by a wide traverse branch (Sinus
intercavernosus) behind and below the posterior part of the pituitary
body. Each is continuous in front with the ophthalmic vein and below
with the inferior petrosal sinus. The third, sixth, and the ophthalmic
and maxillary divisions of the fifth nerve lie along the outer wall of
the sinus. The internal carotid artery traverses the sinus and is
connected with its fellow by a transverse branch which lies in the
corresponding part of the sinus. An oval opening in the floor
communicates with the inferior petrosal sinus and transmits the internal
carotid artery.
The sinus is not subdivided by strands of fibrous tissue as in man,
but a few delicate bands attach the artery to its wall.
The =inferior petrosal sinuses= (S. petrosi inferiores)[172] lie along
the borders of the basilar part of the occipital bone, inclosed in the
thick dura which closes the foramen lacerum. The anterior part extends
about half an inch (ca. 12 mm.) under the temporal wing of the sphenoid.
Here communications exist with veins in the pterygo-palatine fossa. The
posterior end is bulbous and lies in the condyloid fossa; it
communicates with the condyloid vein issuing from the hypoglossal
foramen and is drained by the inferior cerebral vein; it also receives
an emissary vein from the parieto-temporal canal. The roof of the sinus
is perforated by an oval opening at the carotid notch which opens into
the cavernous sinus and transmits the internal carotid artery; the
latter forms the first bend of its =S=-shaped curve in the petrosal and
the second in the cavernous sinus.
The =basilar plexus= (Plexus basilaris) is a venous plexus situated on
the upper surface of the basilar part of the occipital bone. It is
connected through the hypoglossal foramen with the inferior petrosal
sinus and communicates behind with the spinal veins.