THE SUPERIOR CAVAL SYSTEM. 877 



The Cerebral Veins. 



The cerebral veins (vv. cerebri) convey the blood carried to the brain by 

 the cerebral arteries to the sinuses of the dura mater. They differ from most 

 of the other veins in that they contain no valves, their walls are very thin and 

 destitute of muscle-tissue, and their arrangement does not usually follow that of the 

 arteries. 



1. The Superior Cerebral Veins. — The superior cerebral veins (vv. cerebri 

 superiores) are from eight to twelve in number, draining the upper, lateral and medial 

 surfaces of the cerebral hemispheres. They follow, for the most part, the sulci of the 

 hemispheres, although connected across the gyri by numerous anastomoses, and they 

 open above into the superior longitudinal sinus. The various veins show a tendency 

 to increase in size from before backward, and while the anterior ones have a course 

 almost at right angles to the superior longitudinal sinus, the more posterior ones are 

 directed forward as well as upward and open obliquely into the sinus and in a direc- 

 tion contrary to the flow of the blood contained within it. 



2. The Middle Cerebral Vein, — The middle cerebral vein (v. cerebri media), 

 also termed the superficial Sylvian vein, lies superficially along the line of the Sylvian 

 fissure and opens below into either the cavernous or the spheno-parietal sinus. It 

 receives afifluents from the surface of the brain on either side of the fissure and through 

 these anastomoses with both the superior and inferior cerebral veins. One of these 

 afifluents which lies appro.ximately along the line of the fissure of Rolando is usually 

 of large size and communicates directly with one of the superior cerebral veins, the 

 two forming what is known as the great ayiastomotic vein of T^'olard, uniting the 

 superior longitudinal sinus with the median cerebral vein. 



3. The Inferior Cerebral Veins. — The inferior cerebral veins (vv. cerebri 

 inferiores) are a number of small veins which occupy the inferior surfaces of the hemi- 

 spheres. They are somewhat irregular in their arrangement, those of the frontal 

 lobes anastomosing with the superior cerebrals and opening into the anterior portion 

 of the superior longitudinal sinus, while those of the temporo-sphenoidal region 

 anastomose with the middle cerebral and open into the spheno-parietal, cavernous and 

 superior petrosal sinuses and into the basilar vein. 



4. The Great Cerebral Vein. — The great cerebral vein (v. cerebri magna), 

 also known as the great vein of Galen, is a short stem about i cm. in length which 

 is formed beneath the splenium of the corpus callosum in the neighborhood of the 

 pineal body, by the union of the two internal cerebral veins. It passes backward 

 and upward, curving around the posterior extremity of the corpus callosum, and 

 terminates (Fig. 756) by opening into the anterior end of the straight sinus. 



Tributaries. — The great cerebral vein is formed by the union of the two {a) internal cerebral 

 veins (vv. cerebri internae), also known as the small veins of Galen. These are situated, one on 

 either side of the median line, in the velum interpositum, which forms the roof of the third 

 ventricle. Each is formed at the foramen of Monro by the union of three veins, the choroid vein, 

 the vein of the septum lucidum, and the vein of the corpus striatum. The choroid vein (v. chori- 

 oidea ) seems to be the direct continuation of the internal cerebral vein. It begins at the junc- 

 tion of the body and descending horn of the lateral ventricle, passes forward along the floor of 

 the ventricle in the outer edge of the choroid plexus, and opens at the foramen of Monro into the 

 internal cerebral vein of its side. The vein of the septum lucidum (v. septi pellucidi) passes 

 backward along the outer (ventricular) surface of the septum lucidum, returning the blood from 

 the head of the caudate nucleus and neighboring parts, and the vein of the corpus striatum (v. 

 terminalis), which drains the lenticular nucleus and to a certain extent the caudate nucleus also, 

 passes backward in the groove between the corpus striatum and the optic thalamus (stria termi- 

 nalis). 



{b) The posterior vein of the corpus callosum passes backward from about the middle of 

 the superior surface of the corpus callosum and, bending around the splenium, empties into the 

 great cerebral vein or into the internal cerebral vein near its termination. It receives blood 

 from the corpus callosum and from the median surface of the hemisphere. 



(c) The basilar vein (v. basalis) is a large paired vein which arises at the anterior per- 

 forated space by the junction of the deep Sylvian vein with the anterior vein of the corpus cal- 

 losum. It passes backward over the optic tract of its side and then curves upward around the 

 crus cerebri to reach the dorsal surface of the brain-stem, where it opens into either the great or 

 the internal cerebral vein. Occasionally the terminal portion which bends upward around the 



