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COMPARATIVE ANATOMY OF THE APE AND OF MAN. 167
Further on he says, “Language is something more palpable than a fold of the brain or an angle of the skull; it is the one great barrier between the brute and man; it admits of no cavilling, and no process of natural selection will ever distil significant words out of the notes of birds or the cries of beasts. Language is our Rubicon and no brute will dare to pass it.” Without entering into the question of whether the means of communicating with each other undoubtedly possessed by brutes be entitled to the appellation of a language or not, it cannot be denied that one of the great distinctions between man and animals is the possession of articulate language. One of the differences between man and the more intelligent animals is in the degree of development of the cerebral convolutions, which, moreover, exist only in the class Mammalia; and according to Flourens, the Rodentia, the least intelligent of the Mammalia, have no convolutions; the Ruminantia, more intelligent than the Rodentia, have convolutions; the Pachydermata, who are still more intelligent than the Ruminantia, possess still more convolutions, and so on the number continues to increase as we ascend to the Carnivora, then to the Apes, the Orangs, and lastly to Man, who is the richest of all animals in cerebral convolutions. If this gradation in the number of the convolutions has a relation to the intelligence of the animals, it would seem to give an a priori reason for concluding that the highest product of intelligence-speech-may well have some connection with the development of the convolutional grey matter.
Let us consider for one moment the comparison which Carl Vogt makes between our quadrumanous cousins and ourselves. According to this distinguished natural
ist, the Apes have an extremely imperfect development of the third frontal convolution, and the same condition exists in the Microcephali; therefore, he says, as neither Apes nor Microcephali can speak, Comparative Anatomy gives a subsidiary support to the theory which places speech in this convolution. Professor Vogt's views seem to me of such great importance, and so extremely pertinent to our subject, that I shall give them in his own words.
The brain of Man and that of Apes, especially of the anthropoid apes (Orang, Chimpanzee, Gorilla), are constructed absolutely upon the same type—a type by itself--and which is characterised, amongst other things, by the fissure of Sylvius and by the manner in which the island of Reil is formed and covered; but there are secondary differences in the arrangement of the folds, in the comparative development of the lobes and of the convolutions. One of the principal characters is, that in the brain of all the human races, without exception, the frontal lobe, by its posterior and inferior part (that is in Broca's region) touches the temporo-sphenoidal lobe, so as to give the fissure of Sylvius with its two branches, the appearance of a double-pronged fork; whilst in the Apes, Broca's convolution is separated from the temporo-sphenoidal lobe by the lower end of the transverse frontal and transverse parietal convolutions ; in other words, in Man, the third frontal convolution is extraordinarily developed and covers partly the insula, whilst the transverse central convolutions are of much less importance ; in the Ape, on the other hand, the third frontal convolution is but slightly developed, whilst the central transverse convolutions are very large, descending quite to the edge of the hemisphere, and giving to the fissure of Sylvius the form of a V. The cause of this difference dates from the period of embryonic development:—the brain of the futus of any of the Mammalia at a certain age (two months in Man), has the form of a bean with a large infero-lateral sinus corresponding to the insula and the surrounding parts. From the third to the fifth month, this large space becomes covered in Man by the very rapid growth of the third frontal convolution, and by the slow growth of the transverse central convolutions; whilst in the Ape, it is
just the reverse, the space is filled by the rapid growth of the transverse central convolutions, and by the slow growth of the third frontal convolution. To shew the bearing all this has upon the seat of speech, I would refer to the Microcephali who do not speak—they learn to repeat certain words like parrots, but they have no articulate language. Now, the Microcephali have the same conformation of the third frontal convolution and of the central folds as Apes—they are Apes as far as the anterior portion of their brain is concerned, and especially as far as regards the environs of the fissure of Sylvius. Thus, Man speaks; Apes and Microcephali do not speak; certain observations have been recorded which seem to place language in the part which is developed in man and contracted in the Microcephali and the Ape; comparative anatomy, therefore, comes in aid of M. Broca's doctrine.*
I have reason to believe that these views of Professor Vogt are not very generally known in this country, and I need hardly allude to the extremely important bearing they have upon the question at issue. With the view of obtaining some confirmation of the statement of the arrest of development in the third frontal convolution of the microcephali, I have consulted Mr. Marshall's extremely interesting paper in the Philosophical Transactions for the year 1864, in which he gives a detailed description of the frontal convolutions of a microcephalic woman and boy, neither of whom possessed the power of articulation. In both these brains the frontal convolutions are described as being singularly short and defective as compared with their wonderfully tortuous and complex character in the perfect brain; in fact, Mr. Marshall adds that they were far more simple than in the orang's or the chimpanzee's brain. In only one of these microcephalic brains, however, was the want of development most apparent in the third frontal convolution. Further investigations would, therefore, seem necessary before admitting with Carl Vogt that the conformation of the microcephalic brain gives a direct support to the localisation of speech in the third left frontal convolution.
* The above is an extract from an autograph letter with which Professor Vogt has favoured me. In this communication he expresses a doubt whether we shall ever be able satisfactorily to assign “the divers functions" which compose language, to special parts of the brain, until we have a physiological analysis of articulate language, similar to that which Helmholtz has given of sight and hearing.
As far back as 1827, M. Bouillaud instituted a series of experiments upon animals, with the view of determining the functions of the brain, and on several occasions he removed different portions of the cerebral lobes, without impairing sight or hearing; he also removed the entire hemispheres from a chicken, in whom the power of expressing pain by its peculiar cry was retained.* On one occasion he pierced with a gimlet the anterior part of the brain of a dog, from side to side, at a spot corresponding to the union of the anterior with the middle lobes—that is in the immediate neighbourhood of Broca's region. The dog survived the mutilation, but was much less intelligent than before the operation, and although he could utter cries of pain, he had entirely lost the power of barking.† As far as the present inquiry is concerned, I am aware that but little importance can be attached to these experiments, for there is little or no analogy between the cry of a chicken or the bark of a dog, and the articulate speech of a man; still, experiments of this kind may have an
* Recherches expérimentales sur les fonctions du cerveau. de Physiologie, tom. x., p. 49.
+ Ibid, p. 85.
indirect bearing upon our subject, and it would be extremely interesting to know what would be the effect of traumatic injury to certain regions of the anterior lobes upon the quasi-articulatory powers of the parrot.
I think that much valuable information in reference to the seat of speech may be elicited from a more careful study of the affinities and differences between the brain of man and that of animals; but this study, surely, should not be confined to the convex surface, or even to the anterior half of the hemisphere. Professor Rolleston, in a most interesting paper, has called attention to other points of difference between the brain of man and that of apes, and he attaches a great physiological value to the presence or absence of the “bridging convolutions," which more or less fill up the space known as the external perpendicular fissure, which separates the occipital from the parietal lobe.*
Professor Owen mentions the superior development of the hippocampus minor, as a point of distinction between man and the lower animals. According to him, in the inferior mammalia the posterior cornu of the lateral ventricle is capacious and simple, whereas in the chimpanzee and gorilla the growing walls begin to be reduced by the encroachment of a protuberance, which in the archencephala is developed into the hippocampus minor. + It will be remembered that it was in this
* Medical Times, Feb. 22nd and March 15th, 1862.
There are many other points in Dr. Rolleston's paper, which, although having no direct bearing upon speech, afford a collateral aid to that subject, and it is impossible to overrate the value of the talented Oxford Pro. fessor's researches in this direction.
+ Comparative Anatomy and Physiology of the Vertebrates, vol. iii.,