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[373] Professor Owen premised that the cast which he exhibited was not that of the brain of the gorilla, but of the interior of the skull of an adult male of that ape; it, therefore, presented a slightly exaggerated view of the size of that organ; but the proportions of the cerebrum to the cerebellum, and the size and general disposition of the convolutions of the cerebrum, were shown. He contrasted with it the cast of the brain of a man, from the museum of Professor Clark, taken after the brain had been hardened for the purpose, and stripped of its coverings; it, therefore, showed some contraction of size; but the cerebrum and cerebellum being equally condensed, their relative proportions were preserved. The brain of the highest known ape showed no increase of the relative extent of cerebrum over cerebellum beyond that of the small South American monkeys. The cerebrum extended over the cerebellum, not beyond it. He then contrasted the sudden and great development of the cerebral organ presented by a man of the lower order; great increase in absolute size; still greater superiority in relative size to the bulk and weight of the body; the gorilla having the trunk, and head, and upper limbs of a giant, supported on dwarfed, but powerful grasping legs. This evidence of the cerebral organ in the largest and most anthropoid of the anthropoid apes was alone wanting to test the validity of the zoological character of the group represented by man, as given in the author's Classification of Mammalia. Professor Owen then pointed out the close and gradual transition in the Quadrumanous series, from the gorilla's brain to that of the smooth and unconvoluted cerebrum of the marmoset, such simplification of the cerebrum being unaccompanied by difference of its relative horizontal extent to the cerebellum; and he noticed the intermediate exceptions, where, as in the maimon baboon, through the restricted development of the cerebellum, the smooth, unconvoluted posterior part of the cerebrum, even extended beyond the cerebellum,–an exception of that kind, like the long nose of the Semnopithecus nasicus, which serves to prove the rule. Passing on to the Lemurine series, he showed how the still descending cerebral organ graduated into that of the ordinary Feline. The sudden advance of so supremely important an organ as the brain, in the human race, and the marked hiatus between the highest grade of its structure and the next step below, attained by the orangs, chimpanzees, and gorillas, was one of the most extraordinary in the whole range of Comparative Anatomy. It was associated with the intellectual capacities, the power of framing general propositions, and of expressing thought in articulate speech. Parallel with this series, and with a like sudden and great interval between the highest ape and man, was the progression of the modifications of the foot, which were traced up from the Carnivora, though Galeopithecus, the aye-aye, and other lemurs, the platyrrhine and catarhine Quadrumana, up to man. The bones of the foot of the gorilla were contrasted with those in the human subject; the progressive strengthening of the inner toe served only to make the foot a more powerful grasping hand. Not until we arrived at man did that digit present such proportions and position, associated with correlative modifications of all the other bones of the foot, as to change a "hand" into the organ mainly contributory to the erect position, and to justify the innermost being called "hallux," or great toe, for the purpose of succinctly defining the characters of the group, just as the relative position of the hind part of the cerebrum to the subjacent cerebellum affords the zoologist a convenient and precise definition of the posterior cerebral lobe, which human anatomists had failed to find in the structure of the cerebrum itself. The purpose of the present contrast of the brain and foot of the gorillas with those organs in man was to ascertain their value as zoological characters. The grounds on which Baron Cuvier had assigned an ordinal value to the foot of man were briefly given, and the parallel argument was carried out in support of the higher value to be assigned to the differential character of the human brain. Professor Owen then briefly adverted to the chief objections which had been made to his order, Archencephala One was, that the difference of structure was greater between the highest and lowest quadrumanous brains, than between the former and that of man. But, admitting this, it might be as logically objected that there was a greater difference between the foot of the gorilla and the ventral fin of a fish, than between the former and the foot of man. The comparison which really concerned the question at issue was not between remote links in the zoological series, but between the nearest known gradations; and the difference between the gorilla and chimpanzee, in regard to brain and foot, on the one hand, and between the gorilla and the lowest variety of man on the other hand, was that with which zoology was concerned in the present classificatory discussion. A second objection was based upon, and derived its chief strength from, the arbitrary definitions and terms needed in zoological definitions. To the affirmation, that man alone had the hallux, or great toe, an emphatic denial was given, supported by a demonstration of the homologous bones in the hind thumb of the whole series of apes, and even in the short toe sustaining the "dew-claw" of the dog. But if the zoologist has been careful to define his "hallux," the value of such objection became patent. So with regard to the posterior lobe of the brain and its contained structures in man, if the zoologist, availing himself of those and other characters of the human brain, has been duly careful in his definition when availing himself of them for brief and concise zoological differentiations.
The Chairman moved a vote of thanks; and, calling for observations,
Professor Huxley, F.R.S., objected to the comparison of the cast of the cranial cavity of the gorilla with the cast of the brain itself of the man. He quoted Professor Wagner in support of the minor difference of size of brain, at least in a female, than was shown in the brains of the males of the two species compared. Quoting a diagnostic of cerebral characters of man, which he attributed to the author of the paper, he affirmed the incorrectness of assigning to the Quadrumana a cerebrum covering only two-thirds of the cerebellum. On the contrary, the cerebrum extended over the whole cerebellum in the Quadrumana, as low down in the order as the small squirrel monkeys of South America. He adduced the evidence of Dr. Rolleston, Mr. Flower, and Professor Vrolik, in proof of the existence of the posterior cornu and hippocampus minor in such posteriorly-extended part of the cerebrum of Quadrumana, and contended that the difference between man and the ape was psychical, not physical–was manifested by attributes of the mind, not by modifications of the body.
Professor Rolleston, F.R.S., rose to confirm his friend's assertion as to the internal structures in the posterior lobes of the quadrumanous brain. He objected to Professor Owen's diagnosis, that it was limited to characters derived from the back part of the cerebrum; whereas the more important difference between the human and simial brains were shown at the fore part. He reflected on Professor Owen for omitting this consideration; and especially for neglecting the more important grounds of comparison and differentiation afforded by the cerebral convolutions, the characters and homologies of which had been left to be elucidated by the labours of continental anatomists.
Mr. W. H. Flower gave a detailed summary of the various structures he had met with in the posterior part of the cerebrum, extending over the cerebellum, in the Quadrumana; showing in some a greater development of the posterior cornua and hippocampi minores than in the human brain. He specially cited the marmoset monkey as showing a cerebrum co-extensive behind with the cerebellum; and adduced the case of the baboons in which, as Professor Owen admitted, the cerebrum extended beyond the small cerebellum.
The Rev. Mr. Molesworth addressed the Section at some length, chiefly in refutation of Professor Huxley's assumption, that any powers of a living organism could be distinct from, and independent of, its organization; and contended that the superior psychical manifestations of the human species must be associated with concurrent modifications of his bodily frame and organs.
After some remarks from Dr. Humphrey, Professor Owen, in reply, repudiating the terms of the diagnosis of the archen[374]cephalous type of brain ascribed to him, requested that a copy of his work "On the Classification and Geographical Distribution of Mammalia," might be sent for, meanwhile remarking that the ventricular extension in the quadrumanous brain, to which the anthropotomical terms, "posterior cornu" and "hippocampus minor," had been applied, being confessedly restricted to that part of the cerebrum overlying the cerebellum, did not affect or apply to that part of the human cerebrum, which he believed he had clearly and unmistakably defined in his diagnosis of man's cerebral characters. A copy of his work being handed in, Professor Owen first called attention to the figure of the unconvoluted brain of the marmoset monkey (p. 25, fig. 6) illustrating the character he had assigned to the quadrumanous brain in regard to the extension of the cerebrum over the cerebellum. So far from having ignored this structure, as charged upon him by his antagonists, he believed himself to have been the first to point it out, having described and figured the extension of the cerebrum over the whole of the cerebellum in Midas rufimanus, in a paper on Cerebral Anatomy, communicated to the Royal Society in 1836. Then, adverting to Dr. Rolleston's animadversions, Professor Owen read the terms of his diagnosis, as given at page 25 of his work:–"In man the brain presents an ascensive step in development, higher and more strongly marked than that by which the preceding sub-class was distinguished from the one below it. Not only do the cerebral hemispheres overlap the olfactory lobes and cerebellum, but they extend in advance of the one and further back than the other." Here the author remarked that it must be plain to every dispassionate and unprejudiced person, that the part of the cerebrum which man had in common with that which he had figured and described in Quadrumana, co-extensive, viz., with the cerebellum, was not propounded as the differential character of Archencephala, but only the further cerebral developments which were not shown by Quadrumana. Furthermore, that, so far from limiting his diagnostic character to the back part of the brain, he had set forth, and in the first place, the development of the fore part, in which the human cerebrum was peculiar, as "not only overlapping, but extending in advance of the olfactory lobes." With respect to the charge of having neglected the convolutional characters, Professor Owen next proceeded to quote from his diagnosis of the archencephalous brain:–"The superficial grey matter of the cerebrum, through the number and depth of the convolutions, attains its maximum in them."–(Op. cit., p. 26). It was true that he had not entered upon the extent to which the homologous convolutions could be traced in the human and inferior brains in the purely zoological communication which he had submitted to the Linnæan Society in 1857, and in the briefer compendium included in his "Reade's Lecture." (a) But he would ask Dr. Rolleston to refer to a Memoir on the Anatomy of the Felis jubata, communicated to the Zoological Society in 1833 (Zool. Trans., Vol. i, p. 133, pl. 20), in which he would find an early attempt to determine the homologies of the cerebral convolutions. Here they were distinguished into "principal" or "primary," and into those of the "second degree': and homologous ones, determinable in distinct species, were indicated by special letters, figures, and names. Professor Owen also appealed to Mr. Flower to look into the series of diagrams in the Royal College of Surgeons, for those illustrating the course of Lectures given by Professor Owen, when Hunterian Professor, "On the Comparative Anatomy of the Brain," in which the homologous primary convolutions in different orders of mammalia would be found to be distinguished by different colours. At that period, and prior to submitting his ideas on the classificatory value of the cerebral characters in mammalia, Professor Owen has been fully aware of the ventricular extensions in the supracerebellar part of the cerebrum, from the chimpanzee (Vrolik) down to the Lemurine Tarsius (Burmeister); but the assigning to mere fissures the high-sounding names applied by old anthropotomists to the well-marked structures in man, only verbally masked the real differences, and, as affecting the diagnosis which he had quoted, were quite beside the mark, since that part of the diagnosis referring to the back part or lobe of the brain, with its contained structures, was expressly restricted to the part of the cerebrum which extended, not merely over, but further back than the cerebellum. Professor Owen finally advocated to the absence of any comment on the direct purport of his present communication to the Section of Zoology, which had been the zoological significance or classificatory values to be attached to the differential characters of the foot and brain of man. Re-affirming the accuracy of Cuvier's estimate of the former, as indicative of the ordinal value of Bimana, Professor Owen inferred that "silence gave consent" to the higher estimate of the cerebral distinctions, which he had expressed by the sub-class Archencephala, and had now been able to illustrate by the brain of the gorilla.
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