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isochronous to the pulsations of the heart and arteries, or do they cor- 

 respond, at the same time, to those of respiration ? Such is the physio- 

 logical problem, of which I am about to attempt the solution. 



Those authors who admit the existence of motions in the dura mater, 

 do not agree as to the cause which produces them. Some, and among 

 others, Willis and Bagiivi, thought they had discovered muscular fibres, 

 and ascribed these motions to their action: others, as Fallopius and Bau- 

 hinus, attributed these motions to the pulsations of the arteries of that 

 membrane. The dura mater possesses no contractile power; its firm 

 adhesion to the inside of the skull, would, besides, prevent any such mo- 

 tion. The motion observed in this membrane is not occasioned by the 

 action of its vessels; for, as Lorry observes, the arteries of the stomach, 

 of the intestines, and of the bladder, do not communicate any motion to 

 the parietes of these hollow viscera; and yet, in number and size, they 

 at least equal the meningeal arteries. 



The motion observed in the dura mater is communicated to it by the 

 cerebral mass which this membrane covers; and this opinion of Galen, 

 adopted by the greater number of anatomists, has been placed beyond a 

 doubt, by the experiments of Schlitting, of Lamure, Haller, and Vicq- 

 d'Azyr. They have all observed, that on removing the dura mater, the 

 brain continued to rise and fall; and, with the exception of Schlitting, 

 they agreed that the brain, absolutely passive, received from its vessels 

 the motions in which the dura mater partook: but are these motions 

 communicated by the arteries or by the cerebral veins, and by the sinuses 

 in which these terminate; or, in other words, are they isochronous to 

 the beats of the pulse, or to the contraction and successive dilatation of 

 the chest, during respiration. 



Galen, in his treatise on this function, says, that the air admitted into 

 the pulmonary organ distends the diaphragm, and is conveyed along the 

 vertebral canal into the skull. According to this writer, the brain rises 

 during the enlargement of the chest; and it sinks, on the contrary, when 

 the parietes of this cavity are brought nearer to its axis. Schlitting, in 

 a memoir presented to the Academy of Sciences, towards the middle of 

 the last century, maintains that these motions take place, in a different 

 order; the elevation of the brain corresponding to expiration, and its de- 

 pression to inspiration. Conceiving that he has determined this fact by 

 a sufficient number of experiments, he does not enter into any explana- 

 tion; and concludes his inquiry, by asking whether the motions of the 

 brain are occasioned by the afflux of air, or of blood, towards that organ. 



Haller and Lamure attempted to answer this difficulty. They both 

 performed a number of experiments on living animals, acknowledged 

 the fact observed by Schlitting, and explained it in the following man- 

 ner: as well as this last anatomist, Lamure believed that there is a va- 

 cuum between the dura and pia mater; by means of which, the motions 

 of the brain might always be performed. The existence of such vacuum 

 is disproved, by the close contact of the membranes between which it is 

 supposed to exist. 



During expiration, continues Lamure, the parietes of the chest close 

 on themselves, and lessen the extent of this cavity. The lungs, pressed 

 in every direction, collapse; the curvature of their vessels increases, and 

 the blood flows along them with difficulty. The heart and great vessels 

 thus compressed, the blood carried off by the upper vena cava to the 

 right auricle, cannot be freely poured into this cavity which empties 



