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bestowed on the latter who gave a superb dra\ving of the same part. I 

 shall content myself with observing, that the principal arterial trunks 

 going to the brain, are situated at the base of this viscus ; that the 

 branches into which these trunks divide, and the subdivisions of these 

 branches, are, likewise, lodged at its base in a number of depressions, 

 and that, in the last place, the arteries of the brain do not penetrate into 

 its substance, after they have undergone in the tissue of the pia mater, 

 which appear, completely vascular, very minute subdivisi -ns. 



The vessels which return the portion of blood which has not been 

 employed in the nutrition and growth of the brain, are on the contrary, 

 situated towards its upper part, between its convex surface, and the arch 

 of the cranium, each convolution contains a great vein which opens into 

 the superior longitudinal sinus. The vena Galeni which deposits into the 

 sinus, the blood brought from the choroid plexus; small veins which 

 open into the cavernous sinuses; others, likewise very minute, which 

 passing through the foramina in the alse majores of the sphenoid bone, 

 contribute to form the venous plexus of the zygomatic fossa, are the only 

 exceptions to this general rule. 



This being laid down in the arrangement of the arteries and veins, let 

 us examine what will be the effect of their action, with regard to this 

 viacus. 



The contractions of the heart propel the blood into the arterial tubes, 

 which experience especially at the place of their curvatures, a manifest 

 displacement, at the time of their dilatation. All the arteries situated 

 at the base of the brain, experience both these effects at once. Their 

 united efforts, communicate to it a motion of elevation succeeded by de- 

 pression, when by their contraction, they re-act on the blood which fills 

 them. 



These motions take place, only as long as the skull remains entire; this 

 cavity is too accurately filled, and there is no void space between the 

 membranes of the brain. Lorry who, with good reason, denied the ex- 

 istence of sch a space, committed an equally serious anatomical mis- 

 take in asserting, that as no motion could take place, on account of the 

 state of fulness of the skull, it was effected in the ventricles, which he 

 considers as real cavities, but which, as Haller has shown, are, when in a 

 natural state, merely surfaces in contact. No motion actually takes place, 

 except in those cases in which there is a loss of substance in the parietes 

 of the skull. 



It is easy to conceive, however, that the brain which is soft and of weak 

 consistence, yields to the gentle pressure of ics arterial vessels. Does 

 not this continued action of the heart on the brain, explain in a satisfactory 

 manner, the remarkable sympathy between those two organs, linked by 

 such close connections ? It is, besides, of very manliest utility, and con- 

 nected with the return of the blood distributed to the cerebral mass and 

 to its envelopes. The veins which bring it back, alternately compressed 

 against the arch of the skull, empty themselves more easily into the 

 sinuses of the dura mater, towards which their course is retrograde, and 

 unfavourable to the circulation of the blood which they pour into them. 



When any thing impedes the free passage of the blood through the 

 lungs, it stagnates in the right cavities of the heart; the superior vena 

 cava, the internal jugulars, and consequently the sinuses of the dura 

 mater, and the veins of the brain which terminate in them, are gradual- 

 ly distended ; and if this dilatation were carried to a certain degree, the 



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