656 THE VEINS. 



the sinuses of the dura mater, and on the exterior of the skull with the veins of 

 the pericranium. They are divided into the frontal, which opens into the supra- 

 orbital vein by an aperture in the supra-orbital notch ; the anterior temporal, 

 which is confined chiefly to the frontal bone, and opens into one of the deep 

 temporal veins, after escaping by an aperture in the great wing of the sphenoid ; 



( FIG. 382. Veins of the Diploe as displayed by the removal of the outer table of the skull. 



the posterior temporal, which is confined to the parietal bone, and terminates in 

 the lateral sinus by an aperture at the posterior inferior angle of the parietal 

 bone ; and the occipital, the largest of the four, which is confined to the occipital 

 bone, and opens either into the occipital vein or internally into the lateral sinus 

 or torcular Herophili. 



The Cerebral Veins. 



The Cerebral Veins are remarkable for the extreme thinness of their coats in 

 consequence of the muscular tissue in them being wanting, and for the absence 

 of valves. They may be divided into two sets : the superficial, which are placed 

 on the surface, and the deep veins, which occupy the interior of the organ. 



The Superficial Cerebral Veins ramify upon the surface of the brain, being 

 lodged in the sulci between the convolutions, a few running across the convolu- 

 tions. They receive branches from the substance of the brain and terminate in 

 the sinuses. They are named, from the position they occupy, superior, median, 

 and inferior cerebral veins. 



The Superior Cerebral Veins, eight to twelve in number on each side, return 

 the blood from the convolutions on the superior surface of the hemisphere ; they 

 pass forward and inward toward the great longitudinal fissure, where they receive 

 the median cerebral veins ; near their termination they become invested with a 

 tubular sheath of the arachnoid membrane, and open into the superior longitudi- 

 nal sinus in the opposite direction to the course of the blood. 



The Median Cerebral Veins return the blood from the convolutions of the mesial 

 surface of the corresponding hemisphere ; they open into the superior cerebral 

 veins, or occasionally into the inferior longitudinal sinus. 



The Inferior Cerebral Veins ramify on the lower part of the outer and on the 

 under surface of the cerebral hemisphere. Some, collecting tributaries from the 

 under surface of the anterior lobes of the brain, terminate in the cavernous sinus. 

 One vein of large size, the middle cerebral vein, commences on the under surface 



