VEINS OF THE CEREBRUM The Internal Veins of the Cerebrum.—The veins of the cere brum (vence cerebri) are classed as internal and external. The trunks of the internal veins are located largely in the chorioid tela of the third ventricle, near the apex of which the internal cerebral vein is formed: while at the base of this chorioid tela the internal cerebral vein unites with its mate in forming the great cerebral vein.
The internal cerebral vein (v. cerebri interna) is formed by the union of the chorioidal, the terminal and the vein of the septum pellucidum. It runs backward between the layers of the chorioid tela of the third ventricle (Fig. 7), receiving several small collaterals from the tela, from the pineal and quadrigem inal bodies and the corpus callosum; and, finally, it receives the basilar vein from the inferior surface of the cerebral hemisphere.
Under the splenium of the corpus callosum it joins the internal cerebral vein of the opposite side and forms the great cerebral vein.
The great cerebral vein (v. cerebri magna, Galeni) is a short, thick, median trunk, a half-inch long (Fig. I). At the posterior border of the tentorial notch it is joined by the inferior sagittal sinus and then continued as the sinus rectus. This short vein receives collateral tributaries from the gyrus cinguli, from the medial and tentorial surfaces of the occipital lobe and from the superior surface of the cerebellum (Cunningham).
Small nameless internal veins issue from all parts of the ex terior surface of the cerebrum and form the external veins.
The External Veins of the Cerebrum.—The external cerebral veins (vence cerebri externce) are numerous and of large size. They ramify in the pia mater and in the subarachnoid space. They empty into the dural sinuses, as a rule, against the current in the sinuses, and they form two principal groups: The superior cerebral and the inferior cerebral, and a very small group, on the medial cerebral surface, called the medial cerebral veins.
The superior cerebral veins (vence cerebri superiores), twelve or more in number, carry away the blood from the superior surface of the hemisphere. They run obliquely upward and forward into the superior sagittal sinus. Just before emptying into the sinus they receive most of the medial veins.
The Medial Cerebral Veins (Vence cerebri mediales).—They drain the marginal part of the medial surface of the hemisphere. The veins of this group which do not empty into the superior cerebral veins unite and form the inferior sagittal sinus, and the anterior cerebral vein which drains much of the medial surface.
The inferior cerebral veins (vence cerebri inferiores) drain the base of the cerebrum and the lower border of its convex sur face. On the tentorial surface of the hemisphere, from three five of these veins empty into the transverse and superior petrosal sinuses. Those from the temporal and frontal lobes empty into the spheno-parietal sinus and cavernous sinus, excepting the small anterior cerebral vein and the deep middle cerebral vein, which unite with the inferior striate veins in forming the basilar vein. The anterior cerebral vein accompanies the artery of the same name. It drains the gyrus cinguli and corpus callosum, chiefly; and, in the fossa lateralis cerebri, unites with vessels that descend from the corpus striatum, the inferior striate veins, and with the deep middle cerebral vein. The deep vena cerebri media drains the insula and the opercula, in part, and deep in the fissure runs medianward to the fossa lateralis cerebri and helps to form the basilar. The basilar vein (v. basilaris), is formed at the anterior perforated spot by the deep middle cerebral, the inferior striate and the anterior cerebral veins. Running backward it receives additional blood from the interpeduncular structures, the hippocampal gyrus and the inferior horn of the lateral ventricle, and from the mid brain, as it winds around it to empty into the corresponding internal cerebral vein near its termination. In the fissura lateralis cerebri (Sylvii) runs also a superficial vein, called the superficial middle cerebral (v. cerebri media) which receives tributaries from the surfaces adjacent to the posterior ramus and the stem of that fissure and empties into the cavernous sinus; but it may have two other outlets, viz., the transverse sinus and the superior sagittal sinus. The connection occasionally established between the superficial middle cerebral vein and the transverse sinus is called the posterior anastomotic vein; while the great anastomotic vein (of Trolard) is produced when it joins one of the superior cerebral veins. The great anastomotic vein connects the superior sagittal with the cavernous sinus.
There are no lymphatic vessels in either the brain or spinal cord; perivascular lymph spaces carry the fluid to the interior from the subarachnoid spaces.