462 VEINS. 



as reservoirs for the blood. These are the veins of the diploe ; they can only be 

 displayed by removing the outer table of the skull. 



In adult life, as long as the cranial bones are distinct and separable, these veins 

 are confined to the particular bones ; but in old age, when the sutures are united, 

 they communicate with each other, and increase in size. These vessels commu- 

 nicate, in the interior of the cranium, with the meningeal veins, and with 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 



Fig. 237. Veins of the Diploe, as displayed by the Removal of the 

 Outer Table of the Skull. 



vein, by an aperture at 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 ; 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, 

 which is confined to the occipital bone, and opens either into the occipital vein, 

 or the occipital sinus. 



CEREBRAL VEINS. 



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

 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, inferior, 

 internal, and external. 



The Superior Cerebral Veins, seven or eight in number on each side, pass 

 forwards and inwards towards the great longitudinal fissure, where they receive 

 the internal cerebral veins, which return the blood from the convolutions of the 

 flat surface of the corresponding hemisphere ; passing obliquely forwards, they 

 become invested with a tubular sheath of the arachnoid membrane, and open into 



