[395] Prof. Owen, in his Lecture at the Royal Institution, on Tuesday (19th of March), entered upon an exposition of the distinctive characters between the Negro (or lowest variety of Human Race) and the Gorilla, as exemplified by the skeleton and brain, the diagrammatic illustrations of which (reduced in cuts 1-4) had been exhibited at Mr. du Chaillus's Lecture on the preceding evening.
The osteological distinctions were those which he had pointed out in detail in his Lecture at the Royal Institution on Friday evening, February 4th, 1859; and which received confirmatory illustrations in the rich series of specimens of skulls and skeletons of both sexes and of different ages of the Gorilla, brought over by M. du Chaillu.
The cerebral distinctions were equally striking and well marked. The brain of the Gorilla attaining speedily, in accordance with the law of its growth, the size conformable to its relations with the organs of sense and sensorial nerves terminating in it, seems then to be stricken, as it were, by abrogation of the power of further growth; the capacity of the cranium in a young animal with the deciduous teeth, continues to be that, or very nearly that, of the adult, when the skull has received an addition of about six times the amount of osseous matter so disposed to give the requisite force to the jaws and completing the brutish aspect of the full-grown beast. A ready way to obtain the capacity of the cranial cavity is to fill that cavity with millet-seed, to weigh the skull, and then deduct the weight of the empty skull from the filled one. The range of capacity in the male Gorilla was thus found to be from 17 oz. 3 dr. to 19 oz. 5 dr. whilst in the male Negroes’ skulls the range of capacity was from 38 oz. 5 dr. to 51 oz. 6 dr. Tiedemann records an Ethiopian skull with a capacity of 54 oz. 2 dr. 33 gr. troy; the highest capacity in an European skull being 57 oz. 3 dr. .56 gr. troy. The weight of a Negro’s brain has been found to be from 3 1b. I oz. to 3 lb. 9 oz. 4 dr. troy; that of a full-grown male Gorilla may be estimated at from 10 oz. to 12 oz. troy. In regard to the principal parts of the brain, the difference of size of the medulla oblongata is rather in favour of the Gorilla: the cerebellum of the Gorilla is smaller, the cerebrum is much smaller than in the Negro.
The superaddition of convolutional matter to the cerebral hemisphere, during a prolonged period of growth in brains, in man, gives rise to the main distinctions between the human and highest quadrumanal brains. It is seen in the greater relative height, breadth, and length of the hemisphere, especially in their backward growth, whereby they wholly cover and pass beyond the cerebellum. Their convolutions are more numerous, deeper and more sinuous; but in some Negroes’ brains they are more symmetrically distributed than in those of Europeans. Human anatomists have accordingly divided the cerebral hemispheres into "anterior, middle, and posterior" lobes; but the best authors, who have taken their descriptions from nature, had admitted, that the "middle lobes have no exact boundary behind, but pass off very gradually into the posterior lobes"–("Nervous Centres," in "Cyclopaedia of Anatomy.’ iii. p. 672; so that Dr. Todd concurs with Cruvellier in regarding "the division into middle and posterior lobes as purely conventional" in human anatomy. When, however, the human brain is compared with that of the ape’s, an intelligible definition of a posterior lobe can be given by its relation to the cerebellum. All that part of the hemisphere which covers the posterior third of the cerebellum, and passes beyond it may be defined as a posterior or "third lobe." It contains, in man the prolongations of the lateral ventricles, which, "curving backwards, outwards, and then inwards," form the posterior cornu. "Between the middle and posterior horns there is a smooth eminence, called eminentia collateralis, or pes hippocampi minoris; the eminence continued backwards from the pes into the posterior horn of the ventricle is the hippocampus minor; that which is in front of the pes, or eminentia collateralis, being the hiippocampus major. Now the parts the brain peculiar to man at the back parts of the hemisphere are situated behind the transverse line decussating the brains of the Gorilla and Negro in the cuts 3 and 4. Special anatomical details of these several parts, in comparison with the brains of the Chimpanzee and Orang, were then given, and Prof. Owen proceeded, in conclusion, as follow:– The advocate for man’s origin from a transmuted ape contends, that there is a greater difference of structure between the brains of a Gorilla and of a Lemur than between those of a Gorilla and of a [396] Negro; and suiting his definitions to the statement, he affirms that the higher apes possess the "posterior lobe" with the "posterior horn" of the lateral ventricle, and the hippocampus minor, or at least the "rudiments" of the parts which have been alleged to be peculiar to the human species.
It is true that the higher quadrumana have a more developed cerebrum than the lower, and that in this increase there is a growth in the direction in which the cerebrum of man so peculiarly predominates over the brain of all other species. In that background growth, as was shown by Schroeder van der Kolk, in 1849, may be discerned the base or commencement of the out-growth of the parts which characterize the human hemispheres, and that part which in its human development becomes the hippocampus minor is rightly named by the Dutch anatomist pes hippocampi minoris. But to speak of this and of the outward extension of the ventricle, in which it lies as the "rudiments of the posterior cornu of the ventricle and of the hippocampus minor," shows a misconception of the term "rudiment" in philosophical anatomy. The term "rudiment" of an organ is the representative of the totality of such organ in a germinal or undeveloped state,–such as is the narwhal’s tusk in the closed alveolus of the female, the mammary gland and appendage in the male mammal, the pelvis in the whale, the swim-bladder in the fish;–these are veritable rudiments of parts, which become fully developed, and with normal functions, in the other sex or in other animals; animals; the swim-bladder becoming the lung, for example, in Batachia and higher air-breathers.
The stunted tail of the Manx cat is not a "rudiment" of that expressive appendage in our ordinary tabbies,–it is not the representative of the whole cat’s tail in miniature; it answers only to three or four of the caudal vertebrae of the root, the rest of the tail being wanting,–and so the tail may truly be said to be peculiar to the normal cat as compared with the Manx variety.
In like manner, the pes hippocampi minoris in the brain of the Orang and Chimpanzee answers to the part so called in human anatomy, but not to the hippocampus minor, which, as developed and extended in the human brain, and as defined in human anatomy, is peculiar to man. So, likewise, the extension or production of the lateral ventricle "backwards, outwards and then inwards" is peculiar to man; and the base or beginning of such extension in the ape’s brain can only be called a "rudiment" of the posterior cornu, in the sense in which the base or stump of the tail in the Manx cat may be called the "rudiment," or representative of the fully developed tail of the ordinary feline.
With regard to the graver objection of the transmutationist to inferences based upon the broad and unmistakeable distinctions between the human and higher quadrumanal brains, viz., that the difference of size, shape and structure is still greater as between the Chimpanzee and lowest Quadrumane,-the objection might be put even still more strongly by affirming that the difference is greater, in regard to cerebral development and structure, as between the Gorilla and the Opossum: and still more so as between the Gorilla and the Fish, than as between the Gorilla and the human species.
Whatever be the true and deep significance of the fact, there is a gradation of cerebral development from the lowest to the highest vertebrate species; but there are interruptions in this gradation, which are greatest between the cold-blooded and the warm-blooded Vertebrata, and between the class of Birds and that of Mammals. In the latter class, again, there occur marked and singular strides, so to speak, in the development of the brain.
The monotremes and marsupials have no connecting or "commissural " mass of fibres, overarching the lateral ventricles of the brain: such mass makes its appearance abruptly in the rat, shrew and sloth, which in other respects are nearest the Lyencephala, or loose-brained group. In the discussions which followed the reading of Prof. Owen's Paper before the Linnean Society, in 1857, when the breaks in the series of perfectional steps of cerebral structure in the mammalian class were proposed as grounds for the division of the class into primary groups, it was objected that the thickening by transverse fibres at the fore part of the fornix: in the marsupial brain was a rudiment of the corpus callosum, and that therefore it was incorrect to deny the existence of that great commissure in Marsupialia, and to predicate its presence in higher Mammalia as peculiar to, because fully developed in. them. In like manner the beginning of the extension of the hind part of the cerebral hemispheres over the cerebellum, with cerebral concomitant beginning of the extension of the lateral ventricle and its internal convolution, in that direction, as shown by Vrolik and Van der Kolk in the Orang's and Chimpanzee’s brains, was adduced as invalidating the grounds for the definition of the human race by cerebral characters, as a group "Archencephala," equivalent to the other mammalian groups respectively characterized by cerebral structures. These objections were met amongst other arguments by that as to the erroneous application of the term "rudiment," &c., above stated. The real question being, whether the step in advance demonstrable in the mass and structure of the human brain, as contrasted with that of the ape's, is not the same in kind and degree as that which is demonstrable as between the smooth brain of the rodent and of the marsupial. There is a gradational series of improving cerebral structures from the Ornithorhynchus to the Kangaroo in the Lyencephala; but this interval or difference between any two steps in this series is very small compared with that which separates the highest Lyencephale from the lowest Lissencephale. So likewise in the quadrumanous series there is a succession of small steps or improvements of cerebral structures by which the comparative anatomist advances from the brain of the Lemur to that of the Chimpanzee and Gorilla: but the interval or difference between any two steps in this series is truly small indeed, when compared with that vast cerebral expansion and development of new parts, such is the posterior lobes overlapping and stretching beyond the cerebellum, with their posterior cornu and hippocampus minores, which have no existence in the brains of any lower mammalian animals.
THE HUXLEY FILE