120 M. G. Cuvier's Eeport o?i the Researches 



of nerves; that the fibres of communication of its two fasciculi 

 cross there, so that those of the right ascend into the left, and 

 xuce versa ,- that these fascicuh, alter this first enlargement in 

 the Mammifei'ar by an admixture of grayish matter, and after 

 having formed the protuberance known by the name of 2)07is 

 Varolii, separate and take the name of crura cerebri, conti- 

 nuing to send out nerves ; that they again enlarge by a fresh 

 admixture of grayish matter, in order to form the masses com- 

 monly called thalami nervorum opticoi-wii; and a third time, 

 to form those called corpora striata ; that from the whole exter- 

 nal edge of these last enlargements, is given off an expansion of 

 greater or less thick/iess, and more or less folded externally in 

 different animals, entirely covered ■with grayish matter, and re- 

 flected upwards to cover them again, by forming what are 

 called the hemispheres ,• and which, after bending down between 

 tliem, unites itself to that of the opposite side by one or more 

 commissures or fasciculi of transverse fibres, the most consi- 

 derable of which, existing only in the Mammiferae, is called 

 cojpiis callosum. It is also well known that upon the criira ce- 

 rebri, behind the optic thalami, are one or two pair of lesser 

 enlargements, known, when there are two pair, as in the Mam- 

 miferae, under the name of tuberciila quadrigemina, from the 

 first of which the optic nerves appear to take their origin ; 

 that the olfactory nerve is the only one which does not sensi- 

 bly arise from the spinal marrow, or from its branches ; and 

 that the cerebellum, an irregular mass externally white, and 

 internally cineritious, like the hemispheres, but often much 

 more divided by exterior folds, is situated crosswise behind 

 the tuhercnla quadrigemina, and upon the medulla oblongata, 

 with which it is connected by transverse fasciculi, which ai'e 

 called crura cerebelli, and which join it on either side of the 

 pons Varolii. In these masses, so different and so compli- 

 cated, it was necessary to seek the point from which irritation 

 pi'oceeded, and that at which sensation terminated ; it was ne- 

 cessary to ascertain their respective cooperation in the acts of 

 the will; — and this is what M. Flourens has especially laboured 

 to accomplish. 



He has examined, first, how high we must ascend to pro- 

 duce efficacious irritations on the muscular system; and he 

 has discovered a point at which these irritations were power- 

 less ; then })roceeding to the opposite side of the encephalus, 

 he has irritated it more and more profoundly, so long as it did 

 not act upon the muscles : and when it began to act, he found 

 himself again at the same place where its action had stopt in 

 ascending. This is also the place at which the sensation of ex- 

 citations directed against the nervous system stops ; above it, 



punctures 



