ANGIOLOGY 



mastoid foramen; and (4) the occipital, the largest of the four, which is confined 

 to the occipital bone, and opens either externally into the occipital vein, or inter- 

 nally into the transverse sinus or into the confluence of the sinuses (torcular 

 Herophili). 



Fia. 564. Veins of the diploe as displayed by the removal of the outer table of the skull. 



The Veins of the Brain. 



The veins of the brain possess no valves, and their walls, owing to the absence 

 of muscular tissue, are extremely thin. They pierce the arachnoid membrane and 

 the inner or meningeal layer of the dura mater, and open into the cranial venous 

 sinuses. They may be divided into two sets, cerebral and cerebellar. 



The cerebral veins (vv. cerebri) are divisible into external and internal groups 

 according as they drain the outer surfaces or the inner parts of the hemispheres. 



The external veins are the superior, inferior, and middle cerebral. 



The Superior Cerebral Veins (vv. cerebri superiores), eight to tw r elve in number, 

 drain the superior, lateral, and medial surfaces of the hemispheres, and are mainly 

 lodged in the sulci between the gyri, but some run across the gyri. They open into 

 the superior sagittal sinus; the anterior veins runs nearly at right angles to the 

 sinus; the posterior and larger veins are directed obliquely forward and open into 

 the sinus in a direction more or less opposed to the current of the blood contained 

 within it. 



The Middle Cerebral Vein (v. cerebri media; superficial Syhian vein) begins on the 

 lateral surface of the hemisphere, and, running along the lateral cerebral fissure, 

 ends in the cavernous or the sphenoparietal sinus. It is connected (a) with the 

 superior sagittal sinus by the great anastomotic vein of Trolard, which opens into one 

 of the superior cerebral veins; (6) with the transverse sinus by the posterior anasto- 

 motic vein of Labbe, which courses over the temporal lobe. 



The Inferior Cerebral Veins (vv. cerebri inferiores) , of small size, drain the under 

 surfaces of the hemispheres. Those on the orbital surface of the frontal lobe join 

 the superior cerebral veins, and through these open into the superior sagittal 

 sinus; those of the temporal lobe anastomose with the middle cerebral and basal 

 veins, and join the cavernous, sphenoparietal, and superior petrosal sinuses. 



