THE BRAIN. 165 



The Cerebral Veins. 



These are grouped into cortical, basilar, and ganglionic 

 (deep or central). 



The superior cortical veins gather the blood from the 

 outer and inner surfaces of the cerebral hemispheres and ter- 

 minate in the superior longitudinal sinus. They are eight 

 to ten in number, and open into the sinus forward, contrary 

 to the direction of the blood stream, which is backward. 



The basilar or inferior cortical veins collect the blood 

 from the lower and under surface of the cerebrum and 

 empty into the cavernous, superior petrosal, and lateral 

 sinuses. The more important of these are the (a) middle 

 cerebral vein, which accompanies the middle cerebral 

 artery and empties into the cavernous sinus. () The 

 great anastomotic vein of Trolard (which extends from 

 the parietal lobe to open into the superior petrosal sinus. 

 It communicates above with the superior cerebral veins and 

 thus forms a communication between the superior longitu- 

 dinal sinus and those at the base of the skull), and (c) the 

 posterior anastomosing- vein of Labbe (which passes from 

 the middle cerebral vein to the lateral sinus over the outer 

 part of the temporal lobe). 



The central, ganglionic, deep cerebral veins empty 

 into the veins of Galen, which will appear when dissecting 

 the interior of the brain. 



DISSECTION. 



The pia and its numerous vessels are to be removed from the brain. This 

 must be undertaken very slowly. It is best to begin the removal from the 

 cortical surface, then from the inner surface, and finally from the base. Dur- 

 ing this dissection it is well to place the brain in a basin of water, which 

 partially floats it and preserves its contour. 



When working upon the inner surface of a hemisphere do not separate them 

 too widely, or the corpus callosum will be torn through. Do not draw the 

 vessels directly upward, but at right angles to the surface. 



