3i 
structure of the brain and nerves, &c. 
That the cortical part of the brain is the seat of memory, 
is an opinion I have long entertained, from finding that any 
continued undue pressure upon the upper anterior part of the 
brain entirely destroys memory, and a less degree materially 
diminishes it. Pressure upon the dura mater, where the 
skull has been trepanned, puts a temporary stop to all sense, 
which is restored the moment that pressure is removed ; 
and the organ appears to receive no injury from repeated 
experiments of this kind having been made. In hydroce- 
phalus, when the fluid is in large quantity, and there only 
remains the cortical part of the brain and pons verolii con- 
necting it to the cerebellum, all the functions go on, and 
the memory can retain passages of poetry, so as to say them 
by heart ; but a violent shake of the head produces instant 
insensibility. Pressure in a slight degree upon the sinciput, 
produced in one case complete derangement, with violent 
excesses of the passion of lust, both of which went off' 
upon removing, by the crown of the trepan, the depressed 
bone. 
The veins being so minute, and being supplied with valves, 
explains the circumstance of lymphatics never having been 
met with in this organ ; these veins performing that office, 
carrying the absorbed matter into the superior longitudinal 
sinus, which appears more a reservoir than a vein ; for the 
fluid that passes through it is not simply circulating blood ; 
it contains the colouring matter in a decomposed state as 
black as ink, a change we shall find it undergoes in the spleen 
after death. 
The superior longitudinal sinus may be considered as the 
common receptacle of the absorbent veins of the pia mater 
