veins of the brain, placed between it and the arch of the skull, would tend 

 to depress it towards the base of that cavity. If this dilatation, at first 

 sight, were carried beyond the extensibility of these vessels, their rup- 

 ture would occasion fatal effusions. It is in this manner, that some 

 authors have explained sanguineous apoplexy. 



It will be objected, perhaps, that many of the sinuses of the dura mater 

 are at the base of the skull, and that, consequently, their dilatation must 

 tend to raise the cerebral mass. 



But the greater part of these sinuses are connected only with the cere- 

 bellum and the medulla oblongata, of which it has not yet been possible 

 to ascertain the motions. These sinuses are almost all lodged in the edges 

 of the falx and of the teutorium cerebelli. The cavernous sinus in which 

 the ophthalmic vein disgorges itself, the communicating sinuses, which 

 allow the blood of one of these sinuses to pass into the other, are two in- 

 significant to produce a raising of the cerebral mass. Lastly, the resist- 

 ance of their parietes, formed chiefly by the dura mater, must set strait 

 bounds to their dilatation ; the spongy tissue which fills the interior of 

 the cavernous sinuses, still makes this dilatation and the reflux of the 

 blood more difficult, 



CL. It is enough to prove, by reasons drawn frorn^ the disposition of 

 parts, that the motions of the brain are communidfcted to it, by the col- 

 lection of arteries at its base; the fact must yet be established upon ob- 

 servation, and placed beyond doubt, by positive experiments. The fol- 

 lowing are what I have attempted for this purpose : 



A. I have first repeated the observation of some authors, and ascer- 

 tained, as they did, that the pulsations felt on placing the finger on the 

 fontanels of the skulls of new-born infants, correspond perfectly to the 

 beatings of the heart and arteries. 



B. A patient, trepanned for fracture, with effusion on the dura mater, 

 enabled me to see the brain, alternately rising and falling. The rising 

 corresponded with the diastole, the falling with the systole of the arte- 

 ries. 



C. Two dogs, trepanned, exhibited the same phenomenon, in the 

 same relation, to the dilatation and contraction of the arteries. 



D. I removed, carefully, the arch of the skull, on the body of an adult. 

 The dura mater, disengaged from its adhesions to the bones which it 

 lines was preserved, perfectly untouched. I afterwards laid bare the main 

 carotids, and injected them with water. At every stroke of the piston, 

 the brain showed a very sensible motion of rising, especially when the 

 injection was forced at once along the two carotids. 



E. I have injected the internal jugular veins. The cerebral mass re- 

 mained motionless. Only the veins of the brain, the sinuses of the dura 

 mater dilated. The injection having been kept up for some time, there 

 resulted from it a slight swelling of the brain : when driven with more 

 force, some of the veins burst, and the liquor flowed out. The same in- 

 jection being made with water strongly reddened, the surface of the 

 brain became coloured with an intense red. To see clearly this effect, 

 you ought, after removing the arch of the skull, to divide, on each side, 

 the dura mater, on a level with the circular incision of the skull, then 

 turn back the flaps towards the upper longitudinal sinus. 



F. The internal jugular veins having been laid open, while the injec- 

 tion was forced along the main carotids, each time the piston was pushed 

 forward, the venous blood flowed with the greatest impetus j a clear proof 



