Experimental mutilations of the brains of animals must be regarded as afior1ingstill less conclusive evidence ; when a part of the brain is thus removed, the condition of tho whole of the rest of its mass is altered by the removal of the pressure of the skull, exposure to the influence of the atmosphere, interference with the circulation of its blood, &e. It is impossible that a correct conclusion upon any part of the functions of the brain should be drawn from expen ments of this kind ; and the whole of the arguments deduced from them by Rudolphi, 31agendie, and others, may therefore be neglected.
Fully admitting the insufficiency of these, as of some other minor objections to phrenology, we come to the consideration of some which must be regarded as more important. If phrenology were true, it might be expected that its applications would extend through the whole animal kingdom, and that according to the degree in which each mental faculty is developed in each animal, we should find a corre sponding portion of its brain large or small when compared with that of man. Yet this is so far from being the case, that phrenologists aro compelled to rest their opinions almost exclusively on evidence derived from the comparison of the brains of different individuals of the same species, and to suppose that though many faculties are the same in man and the lower animals, yet in each species they are manifested in some peculiar form and structure not admitting of comparison with those of man. This is evidently contrary to the analogical mode of reasoning which we pursue in other instances ; all eyes, all ears, and all organs of smell are formed on the same principles, and so we might presume are all organs of the mind ; so that as by the size or extent of distribution of their nerves we can determine in each animal the power of its sense of smell or sight or hearing, so by the size of a special part of the brain we might in each estimate the energy of some corresponding faculty. Between the vertebrate and the invertebrate animals, for example, there is an abrupt step in the condition of the nervous system; the brain and spinal cord of the lowest of the former class differ widely from the supra-cesophageal ganglion and the gangli ated cords of the latter; we might therefore expect to find an equally sudden deterioration of mental power. Yet none such occurs : but
although the supra-cesophageal ganglion (which may be regarded as the brain of insects) is only so much larger than the rest of their ganglia as is proportionate to the number of organs requiring to be supplied with nerves from it, yet none will deny that many insects exhibit more exalted psychical powers than the majority of either fish or reptiles do. But, taking the vertebrata alone, in all of which there is a certain general plan observed in the nervous system, it is not found that in each order or species, when compared with the rest, the parts of the brain are developed in proportion to the energy of the faculty ascribed to each of them. The phrenological function of the cerebellum, for example, is almost equally powerful in all species; yet the absolute and proportionate size of the cerebellum regularly lessens as one descends through the order of vertebrata, and in the batrachia, in which its supposed function is extremely energetic, it is a mere narrow cord passing across the fourth ventricle. The part of the brain too, which is found decreasing as it is examined in the descending scale of vertebrate animals, is not the anterior, the seat of the intel lectual faculties, but the posterior, in which are placed the organs of the animal propensities. A fair mode of comparison to determine this is to be found in the degree in which the hinder part of the cerebrum overlaps the cerebellum; in man alone does the former ever completely cover the latter; in idiots it often fails to do so ; in monkeys it covers a still less portion ; and continuing to descend through mammalia, the posterior lobes of the cerebrum grow con stantly smaller, and the cerebellum is proportionally more, and at last completely, exposed. From these facts it might be assumed that the posterior lobes are the seat of some intellectual faculties; and such an assumption can be avoided only by believing that there is no analogy between the form of the posterior lobes of the cerebrum in man and manunalia. It is not denied that these apparent anomalies may exist, and yet phrenology may be true ;.but in balancing the proba bilities of its truth or falsity, they must not be neglected.