I must now notice two other hypotheses as to the office of the cerebellum; the first is that of Foville; the second that of Gall. Foville supposed that the cerebellum is the centre of sensation, " the focus of sensibility." The objections which appear fatal to this hypothesis are derived from anatomy and from patholo gical observation. The cerebellum wants that general connection with sentient nerves, (direct as well as indirect,) which might be expected if it performed the office in question. Not one of the nerves of pure sense has any connection with it. Moreover the diseased states of cere bellum do not give rise to any privation of sensibility such as tnight be expected where the centre of sensation was the part involved.
The most celebrated view of the office of the cerebellum is that put forward by the distin guished Gall. Ile supposed that the instinct of propagation has its seat in this organ, and therefore referred to it as the source of all sexual and genemtive impulses.
Gall's view rests on two assumptions; first, that the instinct of generation or of reproduc tion is " the most indispensable and most pow erful of all the instincts ;" and, secondly, that great width of the occipital region of the skull and thickness of the back of the neck indicate great developement of the cerebellum.
It is by reason of the assumed transcendant importance of the generative instinct that so large a portion of the encephalic mass (an eighth or ninth part of the whole) has been assigned by Gall to exercise an exclusive in fluence over it.
This first position taken by Gall seems to me untenable. Can we separate the sexual instinct from the emotions, from those especially which are clearly instinctive in their nature ? I ap prehend not. The same part of the brain would probably exercise its influence upon all the emotional actions. But even if the sexual instinct were separable from the other instincts, it seems very questionable whether it is of that paramount importance a-s to need a separate organ of great magnitude, of complex structure, and of extensive connections with the rest of the cerebro-spinal centre. If we compare it with the instinct of self-preservation, as mani fested in providing either for the wants of the body or for defence aE,,ainst assault, it certainly cannot be admitted to have a superior influence to this the most pressing of all. Yet, even to this instinct, a separate seat has not been assigned in the brain.* The second position which Gall assumes, and which is certainly necessary to the validity of some of the premises upon which his doc trine rests, is, I think, likewise open to strong objection. I cannot understand that great width of the occipital region and thickness of the back of the neck should necessarily indi cate a great developement of the cerebellum. I do not mean to assert that a large cerebellum would not give rise to a large occipital region, but I do assert that great developement of the mesocephale may give rise to the very same external indications. This latter segment of the encephalon is of considerable size, and, as I have shown in a former part of this article, of com plex anatomical structure, and contains all the elements of a distinct centre, while it possesses extensive connections with the cerebral hemi spheres, the cerebellum, and the medulla ob longata. The largest portion of it, however, is independent of the cerebellum, and it is this portion which contains the greatest abundance of vesicular matter, and which has most dis tinctly the characters of a separate centre of nervous influence. Now the position of the mesochephale, in front of and between the hemispheres of the cerebellum, is such that a great dev.elopement of it would push the hemi spheres to each side, and thus, notwithstanding a small size of the hemispheres themselves, the occipital region would become expanded.
The great and pre-eminent size of the cere bellum in the human subject would warrant the belief that the sexual instinct in man far exceeded that of other animals, if Gall's doc trine were correct. Yet this seems by no means to be the case; for, although in man this instinct is more frequently in operation, it cannot be said to influence the whole'system to the same extent as in many of the inferior animals. Surely this instinct is not more pow erful in man than in the feline class, both male and female ;—the common cat, for instance, in which the lateral lobes of the cerebellum are very imperfectly developed ! There are other an imals,likewise, peculiarly distinguished by the strength of this instinct and the re markable extent to which it influences their entire functions. I have already referred to the extraordinary state of polar tension to which the spinal cord of the male frog, or a portion of it, is liable during the state of sexual ex citement. Yet in this animal the cerebellum is very small; nor does it at this period acquire any increase of size ; and, moreover, there is no appreciable difference between the cerebel lum of the male frog and that of the female, which exhibits no indication of increased ex citement at this period. In fishes the instinct
is in all probability strong; and the generative impulse, unaided as it is by sexual commerce; would seem to be dependent, more than in cases vvhere copulation occurs, on the change which may take place in the nervous centre in accordance with the manifestation of that in stinct; yet the cerebellum is by no means large in these animals. Dr. Carpenter refers to the kangaroo as affording a good instance of dis proportionate developement of the cerebellum to the generative instinct. He says, " a friend who kept some kangaroos in his garden, in formed the author that they were the most salacious animals he ever saw, yet their cere bellum is one of the smallest to be found in the class (Mammalia). Every one knows, again, the salacity of monkeys; there are many which are excited to violent demonstrations, by the sight even of a human female ; and there are few which do not practise masturbation when kept in solitary confinement; yet in them the cerebellum is much smaller than in man, in whom the sexual impulse is much less violent." According to Gall and most of his followers mutilation of the genital organs or their decay in the advance of age is attended by marked effects on the cerebellum. If one testicle, be destroyed, a distinct diminution, according to Gall, takes place subsequently in the cere bellar hemisphere of the opposite side. The kind of evidence upon which phrenologists rest their views of this matter will appear from the following specimens : 1. Dr. Gall relates that at Vienna he was consulted by two officers who bad become impotent in consequence of blows from fire-arms, which had grazed tbe napes of their necks. 2. " Baron Larrey," says Gall, "sent to me a soldier who, in undergoing an operation for hernia, had lost the right tes ticle. Several years afterwards his right eye became weak. He began to squint with the diseased eye, and could scarcely any longer distinguish objects with this eye. I examin ed the nape of his neck, in presence of the two physicians who had brought him, and I found the occipital swelling of the left side much less prominent than that of the right side. The difference was so perceptible that the two physicians were struck with it at first sight." 3. Baron Larrey's cases :--a. An artilleryman received a wound from a musket-ball, which traversed from side to side the insertions of the extensor muscles of the head, grazing and dividing the two inferior occipital swellings which correspond to the hemispheres of the cerebellum. This individual experienced a diminution in the size of his testicles, which fell into a state of atrophy. b. A light horseman, of very amorous disposition, received a sword cut, which divided the skin and all the convex portion of the occipital bone through to the dura mater. The right lobe of the cerebellum was seen through the opening of the dura mater, and the slightest pressure upon this organ mused giddiness, fhinting, and convulsive movements. The patient loses sight and hear ing of the right side, experience-s acute pain in the course of the dorsal spine, and tingling in the testes, which in fifteen days were reduced to the size of a bean. 'The patient dies of tetanus, with loss of the functions of sight, hearing, and generation.* On dissection there was great loss of substance at the occiput, the medulla oblongata and upper part of the spinal cord wcre of dull white, of firmer consistence, awl reduced in size one-fOurth. The nerves arising from these parts were likewise wasted. c. A chasseur received a sabre cut, which di vided the skin and e.rternal proluba.ance of the occipital bone, and the extensor muscles of the head cis low down as the sizth vertebra. This min gets vvell, but Larrey states that he de clares " that he has been deprived of his gene rative powers ever since that wound." 4. Gall caused rabbits to be castrated, some on the right side and others on the left. Having had them killed six or eight months afterwards, he finds diminution of the cerebellar lobe oppo site the removed testicle, and flattening of the corresponding occipital swelling. Vimont, however, found no diminution of the opposite lobe of the cerebellum in four rabbits on which castmtion had been effected on one side, and which had been kept eight months; but in four other rabbits, similarly treated, but kept eighteen months, a very perceptible diminution in the opposite lobe of the cerebellum was The results of mutilation of the generauve organs, as obtained by the researches of AI. Leuret, are far from being favourable to Gall's theory. AI. Leuret took the weight of the cerebellum both absolutely, and, as compared with that of the cerebrum, in ten stallions, twelve mares, and twenty-one geldings. The following table shows the results of the abso lute weights.