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casioned, many of which, however, take effect without rupture, and by 

 the mere transudation of blood through the coats of the arteries. These 

 vessels, like the branches arising from their divisions, are lodged in the 

 depressions with which the base of the brain is furrowed, and do not en- 

 ter its substance, till they are reduced to a state of extreme tenuity, by 

 the further divisions they undergo, in the tissue of the pia mater. 



Notwithstanding the proximity of the brain to the heart, the blood 

 reaches it, then, with an exceedingly slackened motion : it returns, on 

 the contrary, with a motion progressively accelerated. The position of 

 the veins at the upper part of the brain, between its convex surface and 

 the hollow of the skull, causes these vessels, gently compressed by the 

 alternate motions of rising and falling of the cerebral mass, to disgorge 

 their contents readily into the membranous reservoirs of the dura mater, 

 known by the name of sinuses These, all communicating together, of- 

 fer to this fluid a sufficiently large receptacle, from which it passes into 

 the great jugular vein, which is to carry it again into the general course 

 of the circulation. Not only is the calibre of this vein considerable, but 

 its coats too, of little thickness, are extensible : so much so, that it ac- 

 quires by injection, a calibre superior to that of the venae cava. The 

 flowing of the blood is favoured by its own weight, which makes a retro- 

 grade course very difficult*. Thus, to sum up all that is peculiar in the 

 cerebral circulation, the brain receives, in great quantity, a blood abound- 

 ing in oxygen ; the fluid finds, in its course thither, many obstacles which 

 impede and slacken its impulse, whilst all uu the cuntrary, favours its re- 

 turn, and prevents venous congestion!. Let me observe, to conclude 

 what I have to say on the circulation of the brain, that of the eye is near- 

 ly allied to it, since the ophthalmic artery is given out by the internal ca- 

 rotid, and the ophthalmic vein empties itself into the cavernous sinus of 

 the dura mater. Accordingly, the redness of the conjunctiva, the promi- 

 nence, the brightness, the moistness of the eyes, indicate a stronger de- 

 termination of the blood towards the brain. Thus the eyes are animat- 

 ed at the approach of apoplexy, in the transport of a burning fever, du- 

 ring delirium, a dangerous symptom of malignant or ataxic fevers. On 

 this connexion of the vessels of the eye and brain, depends the lividity of 

 the conjunctiva, whose veins, injected with a dark coloured blood, indi- 

 cate the fullness of the brain in the generality of cases of suffocation. 



CXLVI. Of the connexion betiueen the action of the brain and that of tlie 

 heart. It is possible, as was done by Galen, to tie both carotids, in a liv- 

 ing animal, without his appearing sensibly affected by it ; but if, as has 

 never yet been done, both the vertebral arteries are tied, the animal drops 

 instantly and dies, at the end of a few seconds. To perform this experi- 

 ment, it is necessary, after tying the carotid arteries of a dog, to remove 

 the soft parts which cover the side of the neck, then with needles, bent in 

 a semi-circular form, passed into the flesh along the sides of the articu- 

 lation of the cervical vertebrae, to apply ligatures to the arteries which 



* In preventing this reflux, there is no use of valves, which the jugular vein is entire- 

 ly without. It is sufficiently prevented, hy the direction in which the blood Hows, and 

 the extensibility of its coats. This great size which the vein can acquire, would have 

 made useless the valvular folds, insufficient to stop the canal, in that great augmenta- 

 tion of its dimensions. Author's Note. 



t The transverse anastomoses of the arteries, at the base of the brain, are very prop- 

 er for distributing the blood, in equal quantity, to all parts of this viscus, Copland 



