# Natural History Review/Series 2/Volume 1/Number 2/On the Affinities of the Brain of the Orang Utang

XX.—On the Affinities of the Brain of the Orang Utang. By George Rolleston, M. D., F. L. S., Linacre Professor of Anatomy.
As an opportunity has quite lately been afforded me of dissecting an Orang Utang, and as the University Museum possesses a considerable number of preparations which illustrate "the Zoological Relations of Man with the Lower Animals," it is less presumptuous in me than it otherwise would have been, to write upon a subject which has met with such able, as well as such recent, handling in the pages of this Journal. The great attention which the Paper to which I allude has attracted, renders it unnecessary for me either to recapitulate the views it propounds, or to specify in detail the points in which I agree, or those in which I feel myself compelled to differ, with the writer of it, whose authority I should be little likely needlessly to dispute.
In this Paper it will be with Human rather than with Simious Brains that I shall contrast and compare the Brain of the Orang Utang; incidentally, however, I shall institute comparisons between the Brain of the Asiatic Ape, and that of the smaller of the two most anthropoid African Apes, the Chimpanzee.
Tiedemann and Buffon exemplify, respectively, the two most opposite views which it is possible to entertain as to the questions of the actual anatomical truth, on the one hand, and of the possible anthropological bearings of the former of these two comparisons, on the other. Buffon, writing in 1766, speaks of the Brain of the Orang in much the same language as Tyson, in his "Anatomy of a Pygmie," had more than sixty years previously, applied to the Brain of the Chimpanzee. Between these Brains and that of Man there was, according to these writers, actually no difference at all—"Le Cerveau est absolument de la même forme et de la même proportion." And the doctrine of the immateriality of the soul was, in the estimation of these authors, not merely compatible with, but a corollary of, these not wholly correct anatomical premises. Though the Brain in each is the same—in the one the power of thought exists, in the other it is absent. Thought, ​therefore, cannot be a product of the Material Organism—"Il ne pense pas—y a-t-il une preuve plus evidente que la matière seule, quoique par- faitement organisée, ne peut produire, ni la pensée, ni la parole qui en est la signe, à moins qu' elle ne soit animée par un principe supérieur?"
The modern Idealist may avoid his predecessors' anatomical errors; but, if he be true to his principles, he will feel no anxiety to repudiate their metaphysics. He may make his strong position yet stronger, we believe, by adducing biological evidence in disproof of the usually granted assumption, that mental capacity stands always in a certain relation to cerebral development; but holding, as he does, the existence of an essential difference between mind and matter, he makes himself but a materialist for the nonce, if he express any repugnance to such statements as those just quoted on account of any conclusions to which they could lead him. For even if they were wholly, as we believe they are nearly, true to the facts, he could draw from them, if he remained true to his principles, no other conclusions than did Buffon and Tyson.
Reasoners of the kind to which we allude will do well to imitate the logical consistency of the materialistic author of the "Icones Cerebri Simiarum." Tiedemann, at all events, had no half-hearted faith in his creed. He plights his faith to the scalpel and callipers, and betrays no anxiety as to any possible upsetting of his conclusion by such data as consciousness or the history of psychical phenomena could furnish— "Parvus ergo encephalus Orang Utangi rationem physicum et certam prodit ubi jam celeberrimus Soemerring monuit cur animi facultatibus tantopere ab homine distet. In homine prævalere cerebrum summumque hominis bonum rationis usum, ab ipsa maxima encephali evolutione pendere haud dubitari potest. Præcipua et essentialis ergo differentia quæ ipsum hominem et reliqua animantia intercedit in cerebro posita est."
Having indicated our opinion that the dealing with such views as those just quoted from Tiedemann's thirty-second Corollary is to be safely, though by no means of necessity, delegated to the metaphysician, we may proceed forthwith to lay before the reader the anatomical details which will enable him to decide for himself, whether the Heidelberg anatomist, or the French natural historian, was the nearer the truth in a matter of fact.
Multitudinous as are the differences which a detailed comparison of any two brains will disclose, they yet admit of being arranged under four heads. Under the first of these heads we may class those differences, which the observant anatomical eye would detect without the assistance of any anatomical instrument, and could express without being necessitated to employ any technical anatomical language.
Our second class of differences comprehends such as the scales and the callipers reveal.
For the power of describing, and one might almost say, for the ​power of discovering the third class of differences, we are indebted to M. Gratiolet's masterly analysis of the cerebral convolutions. Previously to the appearance of the "Memoire sur les Plis Cerebraux de 1' homme et des Primatès," it was all but impossible to express in words the differences which the eye detected in the arrangement in two different brains of what has been called "the chaos of the convolutions." What was previously all but an impossibility, M. Gratiolet's philosophy has made an easy task. No apology can be necessary for adopting his phraseology, as the right of naming the country he has conquered, is a prerogative never denied to one, who has succeeded in subduing a territory which few before him had even thought of invading.
Under our fourth head we shall arrange those points of difference which a dissection of the brain alone can reveal.
These four heads correspond, it is obvious, to the successive stages of an anatomical investigation; and they possess, consequently, the merit not merely of colligating conveniently the results, but also of corresponding accurately to the several processes of an accurate anatomical investigation.
The orang dissected was a young male (Simia Morio). The first two molars had just come into use in both jaws; the weight of the entire body was but 16 lbs. 12 oz.; the height was 2 feet 7 inches. None of the internal viscera presented any appearance of disease. The lungs, which were both but unilobar, were crepitant throughout, free from congestion, collapse, or tubercle. The callosities on the backs of the fingers, which have been held, and with some show of probability, to indicate the existence of a state of debility, were absent.
The roof of the cranium was removed by a circular incision, intersecting the foramen magnum posteriorly. Before the removal of the dura mater, the cerebral hemispheres were seen to cover the superior surface of the cerebellum entirely, and even to project a very little way beyond it, posteriorly. After the removal of the dura mater, a small segment of cerebellar surface became visible on each side, posteriorly to the tips of the occipital lobes. It is well known that the anteroposterior dimensions of the corpus callosum are very different in a brain whilst contained and supported within its case, and when removed from the skull,—the forward swaying of the hemispheres upon their supporting stems, the crura, flattening the previously arched commissure. That it was the weight of the hemispheres, working similarly, which produced the alteration just noted in the relations of the cerebrum to the cerebellum was seen thus'—A wider segment of cerebellar surface was visible on the left side than on the right, the animal lying over towards its right side.
​The greater width of the semilunar segment exposed on the left side was, no doubt, owing to the gravitation of the cerebral lobes, but the greatest width of this segment was only three lines. The relations thus described are well shown in Pl. iii., fig. 3. The view of the base of the brain, as given in fig. 2, will enable us to complete our observations as to the relations of the cerebellum to the posterior lobes of the cerebrum. On looking at that figure, it will be seen that no cerebral surface comes into view on the outside of the lateral boundaries of the cerebellum. In a view of the base of the human brain, some cerebral substance is invariably seen in this situation; but the same is the case with a second orang's brain, with a chimpanzee's brain, and with the brains of several Cercopitheci, and an Inuus, in the Series belonging to the Christ Church Museum. The cerebellum does not project so far laterally as to cover the cerebral lobes in a basal view of any brain in Tiedemann's Icones which is above the rank of the Lemuridæ. Two figures of the brain of the Gibbon given by M. Sandifort, which present a relation of the cerebral lobes to the cerebellum, much resembling that which I have described in the brain of the first of the two orangs in our museum, M. Gratiolet regards with suspicion, whilst he himself records the existence of a similar relation of the two parts of the encephalon in the gorilla. M. Gratiolet gives the figure of the brain of the chimpanzee as drawn by Tyson, only to express a strong opinion as to its worthlessness; and as he condemns it, as well as the two figures of M. Sandifort, on grounds quite independent of the view they give of the cerebellum and its relations, we may, perhaps, be justified in disregarding any evidence which might be based upon these three figures, and in considering the condition and relation of the parts in the subject of this paper as an individual, rather than a specific, peculiarity.
The roof-like exterior of the skull of the gorilla would prepare us for meeting with quite another relation of cerebellum and cerebrum than that which we find in the subglobular skulls of the smaller anthropoid apes. For, though the transverse diameter in these latter skulls taken from one parietal protuberance, or rather from one spot homologous with such protuberance to the other, is only subequal to the transverse diameter, as taken from one supramastoid region to the other, it is yet never markedly inferior, as is the case with the gorilla, to a degree for which no development of mastoidal air-cells can account.
The evidence, then, for the lateral predominance of the cerebellar lobes rests upon the single instance, the subject of this paper, and upon the three representations which M. Gratiolet sees, upon other grounds, good cause for condemning. Against it, is to be set the evidence based upon the examination of several other simious brains as above specified, upon the unanimous assent of every one of the plates given by M. Gratiolet in his Mémoire sur des Plis Cerebraux, and upon Tiedemann's ​figures of the brains of the Simia Rhesus, Simia Nemestrina, Simia Sabæus, and Cebus Capucinus. If the weight of this latter mass of evidence is not sufficient to make us consider the relations of the parts as seen in our specimen, fig. 2, as mere individual peculiarities, it is at all events sufficient to justify us in denying them, not merely all classificatory, but also all physiological value.
For arrogating importance to any projection or predominance backward of the cerebellum, still less justification exists. For so doing no other colour can be brought forward than such as our own figures can afford, for which we have adduced a sufficient explanation—or such as certain confessedly imperfect figures, taken as they were from a confessedly badly preserved brain, may be thought to furnish, when weighed against the all but unanimous verdict to the contrary, which is obtained by the examination of authentic representations, and of well-preserved specimens. In every specimen, save the single one the subject of this paper, of a simious brain above the grade of a lemur, contained in our Museum, the cerebellum is as much covered posteriorly by the cerebral lobes as we have already shown it to be laterally. The same remarks apply to every one of M. Gratiolet's own figures; the only exceptions to the rule which his plates offer being those which the imperfect figures of Tyson and Sandifort furnish. Tiedemann's Icones of the lower apes are unanimous on the same side, but the figures which he gives of the brains of the orang and chimpanzee, in his work on the Brain of the Negro, represent the cerebellum uncovered, on both sides, to a somewhat greater extent than it is in our figures 3 and 4, on one side.
A careful study, however, of our figures, coupled with an examination of the skulls of several anthropoid apes, will lead to the belief that the cerebral hemispheres of the apes bulge less laterally than do those of man; that they are not merely more boat-shaped, and tapering anteriorly and posteriorly, but that they are more wall-sided, and less protuberant laterally.
Though we may be inclined to consider the diminution in lateral expanse, and in backward growth of the posterior lobes, D, of which ​our figures speak, as an individual rather than as a specific peculiarity, we are compelled to assign greater importance to the curtailment in downward growth to which they, as well as other similar figures, testify. A line drawn along the edge of the cerebral hemisphere in Fig. 1, where that hemisphere overlies the cerebellum, will be seen to be much less nearly horizontal than a line is which holds the same relation in a human brain. It seems as if the cerebellum had encroached upon the cerebral lobes which roofed it over.
The same figure shows that a similar stunting has befallen the upward growth of both the frontal and posterior lobes, a line bounding the superior edge of the hemispheres from D forwards to A, describing a much more even curve than is usual in man.
Less ambiguously does the vertical direction of the fissures of Sylvius, F, and of the convolution 6, 6, 6'; parallel with, and immediately below the lower lip, 7, 7, 7, of that fissure, speak of diminished relative anteroposterior growth of the frontal lobes.
The greater relative thickness of the nerves is well seen in Fig. 2.
These nine points of greater or less discrepancy between the human and the Simious brain may be arranged under our first head: they consist, in the ape, of diminution in downward, lateral, upward, and anteroposterior growth, first, of the posterior; secondly, of the frontal lobes; and to these, based on consideration of diminution, we have to add the ninth, based upon a consideration of increase, that, viz., of the size of the nerves. What is the value of these points as differentiating characteristics? Two canons may be laid down, to assist us in estimating the value of such characteristics as means for settling the relative rank of rival organisms. The first of these may be thus expressed:—If certain structures, or certain relations of certain structures, are found to exist in animals confessedly lower in the scale of life than those which are the subjects of comparison, the presence of such structures, or of such relations of structures, cannot by itself he held to be a mark of serial elevation. Cumulatively it may have weight, absolutely it can have none. The second canon is but a converse of the first; and, expressed in similar language, it may run thus:—If certain structures, or certain relations of certain structures, are found to exist in animals confessedly higher in the scale of life than those which are the subjects of comparison, such structures, or such relations of such structures, cannot by themselves be held to be marks of serial degradation. Cumulatively, they may be of weight; absolutely, they are not. These canons have been, perhaps necessarily, expressed in complex language; in themselves, however, they are sufficiently simple and self-evident, and, being so, are compatible with either view of the origin of species.
The first of these canons we have already applied, in our comparison of the overlapped cerebellum of the lower monkeys with the partially unoverlapped cerebellum of our orang. The even curve described by the boundary line of the superior surfaces of the Irishwoman's brain, as given by M. Gratiolet in the first plate appended to his often-quoted work, and the anteriorly and posteriorly tapering ends of the ​hemispheres there figured, enables us to apply the second canon to the several marks of degradation spoken of, as diminution of upward and of lateral growth in the frontal and the occipital lobes. The even regular curve, indeed, of the skull, and its narrowing tapering frontal and occipital regions, as seen in the lower races, would have led us to anticipate some such cerebral conformation as the unhappily all but unique specimen of such a brain as the one just referred to actually discloses to us.
The foramina for the nerves in the skulls of the lower races of mankind have been said by certain ethnologists to present larger diameters than the similar foramina in the basis of the skull of higher races; and if this be really the case, our first canon will come to apply to our ninth point of difference, the larger relative size, namely, of the nerves in the simious brain.
The three points of diminution in downward development of the posterior lobes, and in both downward and in antero-posterior development of the frontal, remain unaffected by the application of either canon. Of their value our figures will enable the reader to judge for himself.
After comparing our single brain of the chimpanzee with the two of the orang we possess in our Museum, we cannot see that the African ape contrasts in any one of these nine points to disadvantage with the Asiatic.
Under our second head—that, namely, of the differences which weighing and measuring enable us to enucleate as existing between the several subjects of our comparison—we have eight points of difference to enumerate. When it is not otherwise specified, the measurements of the human brain were taken from a brain of a German of average intelligence, the brain having recently been brought to the museum and presenting nothing peculiar, in the way either of under or of over development, to render it unfit to serve as a standard of comparison to the brain of the orang. Both sets of measurements were taken at the same time.
The entire weight of the orang's body being 161b. 12 oz., the weight of the brain was 12 oz. The relation of the weight of the brain to that of the body was, therefore, as 1 : 22.3.
The brain : the body = 1 : 11.
​The state of emaciation in which this child is reported to have died makes it the fairer to take it as a standard in this comparison. The child's dentition may very well have been in the same state as that of our orang; its age, however, was in all likelihood much further advanced; but as the brain would have been growing rapidly during those years, whilst the weight of the body was not increased proportionally, the excess of years may not in reality have caused in this case any diminution in the relative disproportion of the child's brain to its body, as it does in cases of healthy development.
On the other hand, we must recollect that the proportion subsisting between the adult brain in man and the body has been put as low as 1 : 50; and that though this proportion is lower by as much as 15 than most authorities would rate it, some such disproportion must have prevailed in those cases in which the brain of an adult Negro is recorded as reaching no greater weight than 753 grammes or 1 lb. 10.59 oz.
The weight of the body of a nearly adult female chimpanzee is given by Professors Sharpey and Ellis, on the authority of Professor Owen, as 61 lb. The relation of weight between such a body and the brain of our orang which weighed 12 oz. would be 1 : 81.3.
Let us suppose that the Negro, the weight of whose brain, as given by Tiedemann, amounted to no more than 26 oz., weighed altogether as much as 8 stone, or 1792 oz. The proportion between his brain's weight and his body's would then have stood as 1 : 68.9, as against a proportion taken between analogous weights in the apes of 1 : 81.3. It will be seen from this that the absolute weight of the human brain is a more sharply differentiating characteristic than is its relative weight.
It will be convenient to give the following measurements and their mutual relations in a tabular form, using, for the sake of economy of space, the letters of the alphabet to denote each particular measurement:—
a. The length from the root of the olfactory nerve to the anterior extremity of the brain.
b. The length from the point of the middle lobe to the posterior extremity of the brain.
c. The length of the cerebellum.
d. The breadth of the cerebellum.
e. Length of cerebral hemispheres.
f. Length of corpus callosum.
| a : b | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | In Orang = 13/4 inch. : 27/8 inch. = 1 : 1⋅64. |
| a : b | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | In Man = 25/8 inch. : 51/8 inch. = 1 : 1⋅95. |
| a : b | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | In Chimpanzee = 44 mm. : 69 mm. = 1 : 1⋅56. |
| c : d | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | In Orang = 11/4 inch. : 3 inch. = 1 : 2⋅40. |
| c : d | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | In Man = 11/2 inch. : 41/8 inch. = 1 : 2.75 |
| c : d | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | In Chimpanzee = 15⋅5′′′ : 32⋅5′′′ = 0⋅48 : 1. |
| e : f | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | In Orang = 41/4 inch. : 17/8 inch. = 1 : 0⋅44. |
| e : f | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | In Man = 6 – 7 in. : 3 – 4 in. = 1 : 0.50 or : 0.42 |
| e : f | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | In Chimpanzee = 99mm : 43mm = 1 : 0⋅43. |
The following six measurements of height, breadth, and length of the human cerebral hemispheres, are the three maximum and the three minimum measurements given by Husche, at the ninety-ninth page of his work, already referred to.
From these measurements, it is evident that the variations of height oscillate within narrower limits in the human brain than the variations either of length or of breadth. The measurement of height, therefore, would seem to possess greater serial importance than either of the other two measurements. Yet the following measurements will show that it is precisely in this dimension that the brain of the apes stands in the greatest relative inferiority to that of man.
Length of hemispheres in Orang : length in Man = 41/4 in. : 6–7 in. = 1 : 1⋅4 or 1 : 1⋅64. „Chimpanzee :„= 99 in. : 6–7 in. = 1 : 1⋅54 or 1 : 1⋅79.
Breadth of ditto in Orang : breadth in Man= 31/4 in. : 4–7 in. = 1 : 1⋅23 or 1 : 2⋅15. „Chimpanzee :„= 95 m. : 4–7 m. = 1 : 1⋅08 or 1 : 1⋅88. „„„= 87 m. : 4–7 m. = 1 : 1⋅17 or 1 : 2⋅06.
Height of ditto in Orang : height in Man= 21/8 in. : 5 = 1 : 2⋅35. „Chimpanzee :„= 54m. : 5 = 1 : 2⋅38. „„„= 64m. :5 = 1⋅2.
Of all the differences of measurements and their relations as yet adduced, the difference between the relative heights of the human and the simious brains seems the most important.
Small as the difference in the two measurements of corpora callosa may seem, we must yet record that posteriorly to the posterior bourrelet or rounded edge of that body in the orang, the corpora quadrigemina came into view when the brain was removed from the skull. This observation will be seen later to have, when coupled with certain others, considerable value, as showing the greater relative shortness of the corpus callosum. It was noticeable that the anterior pair of corpora quadrigemina were less sharply marked off from the posterior than in man.
The central notch of the cerebellum was much shallower relatively ​than in man, a point to be recollected in connexion with the relations stated to exist between the transverse d and antero-posterior diameters c, of the cerebellum.
It is under our third head, that, namely, of the differences which M. Gratiolet's work has enabled us to describe, and we might almost say to discover, that the most important points of our comparison will be found. Under this head will fall the points which were mentioned in the last number of this Journal, as the second and third points of difference, absolutely distinguishing the brain of man from that of the ape; and under it also may be ranged those which M. Gratiolet lays stress upon, as indicating a relative inferiority in the African to the Asiatic ape.
To begin with "the external perpendicular fissure." This fissure or a part of it is visible in Fig. i., below a; in Fig iii., between a and a. It is well represented in most of the simious brains figured by M. Gratiolet; it may be seen in Fig. i., Fig. ii., Fig. iii., Fig. vi., at f, in Tab. i. of Tiedemann's Icones of the brain of the Simia Nemestrina, Simia Rhesus, Simia sabæa, and Cebus capucinus. It will be seen a little later that it is not beside the purpose to remark that it may also be better seen in Tiedemann's figure of the brain of an Orang on one side than it is on either side of his representation of the brain of a Chimpanzee; and that it is very well-marked on both sides, in a drawing of a brain of a young orang given by Professor Wagner, in a work written with express and constant reference to M. Gratiolet's labours. Lastly, this fissure is very well seen in the representation of the brain of the Chimpanzee given by Professor Owen in his paper in the Linnæan Society's Proceedings, Jan. 21, 1857, Fig. iv., p. 19, and in his Reade Lecture, Fig. vii., p. 25.
The inward prolongation of this fissure is never filled up, see 16, Fig. iv. It is upon the degree to which its outward prolongation is filled up or not filled up, bridged or not bridged over, that the absence or presence of an external perpendicular figure, the existence or non-existence of an "operculum," depends.
In the figures referred to, and to some extent in those appended to this paper, the anterior edge of the occipital lobes is seen to rise wave-like as it were against the table-land of the fronto-parietal lobes. The wave-like edge is the "operculum." Along the middle line on each in Fig. i., Fig. iii., and Fig. iv., the wave-like edge, speaking of disruption of continuity between the occipital lobes and the mass of brain anterior to them, is absent; a convolution, a, a, passes across what would else be a chasm. This convolution is the "premier pli de passage" of Gratiolet; it comes according to that authority thus to the surface, and thus bridges the chasm in Man, in the Orang, and in the Ateles, but in no other ape. Our first canon can be immediately applied in the estimation of the value ​of this structure upon the data thus pat before the reader upon the authority of M. Gratiolet. Leaving the task of so applying it to the reader, I shall proceed to show that the superficial position of this bridging convolution is by no means an universally present characteristic either of the human brain, or of the Orangs; and, thirdly, that it is sometimes both present and superficially visible in the brain of the Chimpanzee.
Of seven human brains at present in the University Museum, three possess this bridging convolution on both sides entirely superficial in position; in the fourth we find it wanting on one side, two spurs thrown out from the declivity of the occipital representing what is a perfectly continuous chain on the other side; in the fifth it is concealed on one side by the overhanging edge of the occipital lobes; in the sixth it does not quite reach, on the left side, the level held by the occipital and parietal lobes which it connects; in the seventh, a deep chasm is visible on both sides; but on the left the convolution, which seems to fail to bridge the fissure, does really cross it and fill it up, though at a distance of as much as an inch from the longitudinal fissure ; whilst on the right side the connecting convolution dips vertically downward, and leaves a deep valley between the occipital and parietal lobes. This seventh brain belonged to a man who, by trade a gardener, was possessed of more than an average share of intelligence, and whose brain was carefully preserved for this reason, as well as on account of its great size, and the development of its convolutions. This last of the seven brains will allow us to apply our second canon to test the value of the absence of this structure in the particular relation of superficial position as a mark of serial degradation.
But a structure which exhibits so much variability, as to conform to the rule in but three, and to diverge more or less from it in four, out of seven brains chosen at haphazard for examination, as being all at that moment which a particular museum contained, will scarcely seem to merit a high place as a zoological differentia. With reference to the "premier Pli de Passage" in the orang, a careful comparison of the relations of the parts lettered aa, in fig. 3, with the same relations in fig. 4, will show that this convolution is by no means superficial in its entire extent on the left side of that brain. And, secondly, in our second specimen of an orang' s brain, this convolution is concealed on both sides within the fissure; and the cerebral hemispheres in this specimen pre- sent, in consequence, as perfectly wave-like an opercular edge as in any other monkey. In confirmation of this, I would appeal to Tiedemann's and Wagner's figures, already referred to, as giving typical representations of an external perpendicular fissure in the brain of orang utangs, in which, according to M. Gratiolet, it should be invariably half- filled up by his "premier pli de passage."
Lastly, with reference to the chimpanzee: one specimen possesses ​on its right side a well-marked, superior bridging convolution, coming for a considerable part of its length nearly or quite to a level with the lobes it connects. Tiedemann's figure of the chimpanzee's brain leads us, by its imperfectly-marked operculum, to the same conclusion as its sharply drawn one did in the case of the orang. The law of correlation of forms is a safe guide to us, when we have to predict what will be found in the lower organisms of well-marked families; it loses its in- flexibility, and becomes but a leaden rule, when we come to examine the most perfectly evolved species in such families. In the higher species of the order, apes, as in the higher varieties of the species, man, we find variability the rule, uniformity the exception; in the lower species, as in the lower varieties of man, the reverse condition obtains. The variability which we have seen to exist in the species chimpanzee, is no inconsiderable proof of its high relative rank in its own order.
But there is a second connecting bridge passing between the occipital and the parietal lobes. This convolution is invariably present, and invariably superficially placed in man; it is as invariably absent in both the anthropoid apes. In man it is always a large, easily recognizable structure; and in cases such as those which our fourth human brain may be taken to exemplify, or exaggerate, it will often be found to send a branch, as it were, in aid of the weakened superior bridge. The vacuity which in the apes corresponds to what is invariably a convolution of importance in man, may be seen in fig. 1, immediately posteriorly to 6; and in fig. 3, immediately below a. But this convolution, the "deuxième pli de passage" of Gratiolet, absent without exception in the Old World apes, and present equally invariably in man, is found also in two New World monkeys, the cebus capucinus possessing it without, the ateles possessing it in company with its fellow.
There is yet a third structure—"the Lobule of the Marginal Convolution"—to be treated of. In man it lies above the upper end of the fissure of Sylvius; and it may not unfairly be represented in our figure 1, by the convolution which lies immediately to the spectator's left of 5. Of it M. Gratiolet speaks in the following language:—"Cet lobule est particulier à l'homme et ne se trouve pas ni dans l'orang ni dans le chimpanzee." But I find nowhere in M. Gratiolet's work any repetition of this striking statement: indeed it loses a good deal of its force, when we find the qualifying words "souvent assez grand" applied to this peculiarly anthropic lobule in the sentence immediately preceding the one we have quoted. And in the coloured diagrams, which speak so plainly, by their various hues, of the varied relations in extent and arrangement which may obtain among different brains, I find no separate colour assigned to this peculiarly separable lobe—no such distinction is awarded to them as there is to the bridging "plis de passage;" which, nevertheless, are not asserted to be ​exclusively anthropic. These considerations make me suspect that more weight has been attached to M. Gratiolet's words, as above quoted, than he would have wished them himself to carry; and anatomical investigation seems to me but to strengthen the argument based upon these literary considerations. For this "lobule of the marginal convolution" is very frequently asymmetrical on the two sides of the same brain, and its development in any two human brains taken at haphazard is pretty sure to present the very greatest differences. Varying, as it does most widely, in absolute size, it varies also showing "rien de constant" in its relation to certain other parts; its value can hardly be high, therefore, as a serial characteristic.
The convolution numbered 4 in Fig. 1 and Fig. 3, the "premier pli ascendant" of Gratiolet, is separated by a vertical more or less interrupted fissure from the horizontal-lying frontal lobes 2 and 3. Now, a line drawn down the long axis of this fissure would fall a considerable way in front of the commencement of the fissure of Sylvius. Such a line in the human brain falls always far behind the commencement of that fissure, joining it, indeed, some way behind the angle where the fissure of Sylvius makes its bend horizontally backwards. The forward position of this line speaks more strongly than can the vertical direction of the fissure of Sylvius, of stunted antero-posterior growth of the frontal lobes, and it deserves more attention than it has as yet received.
The convolutions, No. 3, the superior frontal convolutions, are of all the convolutions those in which by symmetry and simplicity, both alike sure marks of degradation, the orang's brain contrasts to the greatest disadvantage with man's. But this fourth and this fifth point we shall leave to be elucidated by the reader for himself from an examination of our figures. We will state, however, the details which an examination of the chimpanzee's brain, instituted with a view of seeing whether its convolutions were really more symmetrical and more simple than those of the orang, elicited, in confirmation of M. Gratiolet's views.
In the orang, and in the chimpanzee, both the frontal, 1, 2, 3, the 4 and 5 ascending parietal, and the superior bridging convolutions aa, are asymmetrical on the two sides of the brain. The occipital d, the temporo-sphenoidal b, and the convolutions b, b, b, named "pli courbe" by M. Gratiolet, are symmetrical in the chimpanzee, but asymmetrical in the orang. The occipital lobe is both more simple and more symmetrical in the chimpanzee than in the orang, but it is not larger in size. Both ascending convolutions are a little more simple in the chimpanzee than in the orang. But the sum total of advantage accruing to the orang from this comparison is, on M. Gratiolet's own principles, but slight.
Having arrived at our last head—that, namely, of such differentiæ as are detectible by dissection only—we will proceed to lay them before ​the reader in the shape of a short account of the dissection which disclosed them.
The right cerebral hemisphere was removed down to the level of the corpus callosum, as seen in Fig. 4. At a point relatively much further distant from its posterior edge, 14, than is the case in man, we see the internal perpendicular fissure, 16. Posteriorly again to this fissure, and running nearly parallel with it, we see a second, 17, the "scissure des hippocampes" of M. Gratiolet. Corresponding with this indentation, we have within the cavity of the ventricle an eminence, 19, the lesser hippocampus, bounded by an arm or creek running up, 18, along its outer surface from the central ventricular expanse. This arm or creek was called, by another metaphor than those we have used, the third cornu of the lateral ventricle, in the phraseology of the old anatomists. The large smooth headland into which the hippocampus swells at 19, justifies the expression we find at page 19 of M. Gratiolet's work—"L' anfractuosité d' ergot . . . qui est plus evidente encore dans les Singes que dans l' Homme." In the brain of a cercopithecus now before us, its proportions are very much larger. The width of this third cornu was at its commencement three-eighths of an inch; and the similar cavity in a human brain examined at the same time was of the same width. But the cavity narrows much more rapidly in the orang than in man; and before reaching its termination, at a distance of one inch from its commencement, it becomes almost a linear cavity; but, as our figure shows, the distinctness of its limiting walls and the continuity of its lining membrane were unambiguously visible up to its very extremity. The length of this third cornu is as great absolutely, and relatively, therefore much greater in the cercopithecus, than in the orang. In the human brain it was but half an inch longer than in the orang, scooped out though it was in a posterior lobe relatively very much longer. Neither in the cercopithecus, nor in the orang, does the bourrelet or posterior rounded edge of the corpus callosum extend nearly so far back as to allow us to take it as "the best measure of the position" of the third cornu; indeed, when we find Tiedemann speaking of the pedes hippocampi minores as "Processus duo medullares qui a posteriore corporis callosi margine proficiscuntur," it is easy to understand how he came to overlook their existence altogether, "in cerebro Simiarum desunt," being so far in error as to their relations to neighbouring parts.
This relation of the posterior edge of the corpus callosum to the commencement of the third cornu is of importance, not merely as a guide to the discovery of that fissure, but also as, when coupled with the relations which the corpus callosum holds to the internal occipital figure 16, laterally, and to the corpora quadrigemina posteriorly, speaking unambiguously of great diminution of the antero-posterior diameter of the simious corpus callosum.
​The hippocampus major presents several well-marked corrugations on its expanded lower extremity, "quæ huic parti tanquam figuram digitorum pedis tribuunt;" but as they are on its posterior, not on its anterior edge, we are not compelled to contradict Tiedemann's twenty-first corollary, which relates to the hippocampus major, in the same way as our figures compel us to differ from his twenty-second, quoted above, with reference to the hippocampus minor.
It is for the sake of illustrating yet further the important principle, that variability of arrangement is to be expected, rather than wondered at, in organisms as high as those of these apes, that I add the following observations as to the convolutions on the internal aspect of the hemispheres. There is scarcely any indication of a lobulus quadratus, the structure representing it resembles but little the figure of it as given by M. Gratiole in his third plate; whilst, as if in compensation, the superior marginal convolution, spoken of by him as "trèe simple et à peu près lisse" dans l' Orang (page 49 in his Mémoire), presents, in our specimen, abundant and rich convolutions.
The internal anatomy of the simious brain does not furnish us, then, with those sharply differentiating characteristics which have been supposed to put it into a position of such marked inferiority to that of man.
As to the external anatomy, whilst too little importance has perhaps been assigned to the points of difference which the very widely-differing heights of the hemispheres, the very widely-differing antero-posterior diameters of the corpora callosa, and of the frontal lobes, and the very widely-differing absolute weights of the two brains, constitute, too much seems to have been given to the "absence of an external perpendicular fissure," to the "presence of a lobule of the marginal convolution," and to the lesser relative size of the nerves in the human brain. Upon most other points, I find myself in agreement with most other writers, both as to facts and to inferences; the cumulative weight of the many minor points of agreement and difference, the reader will be best able to appreciate, by massing each order of facts together for himself.
The principles of the idealist teach him that the difference which exists between the soul of man and the life of the beast which perishes, is not one which can be weighed or measured, be drawn or figured, be calculated in inches or ounces. He fearlessly acknowledges that the anatomical truth in this matter lies on the boundary line of the conterminous positions taken up by Buffon and Professor Huxley, respectively; for he feels that yet higher truth is expressed in the golden words but recently rescued from long oblivion—
"On earth there is nothing great but man; In man there is nothing great but mind."
Description of Plates.
These four views of the brain of the orang are copies of photographs taken of it by Messrs. Hills and Saunders, of Oxford. The brain had been carefully hardened in spirit for as much as two months before it was thus photographed. The figures are numbered in the order in which the photographs were taken. The numbers placed upon the convolutions on the exterior surface of the brain will be found to correspond with those similarly employed by M. Gratiolet in his invaluable Mémoire sur les Plis Cérébraux de 1' Homme et des Primatés, so often referred to.
i. To the commencement of the third cornu, 18. ii. To the internal perpendicular fissure, 16.
2. Middle frontal.—"Étage frontal moyen."
3. Superior frontal.—"Étage frontal supérieur."
4. Eirst ascending parietal.—"Premier pli ascendant."
5. Second ascending parietal.—"Deuxième pli ascendant."
5'. Lobule of second ascending parietel.—"Lobule du deuxième pli ascendant."
6 and 6'. Convolution running below, and parallel with the lower lip of the Sylvian fissure.—"Pli courbe."
7. Lower lip of Sylvian fissure.—"Pli marginal inférieur."
10. Superior occipital convolution.—"Étage superieur du lobe occipital."
11. Middle occipital convolution.—"Étage moyen."
12. Inferior occipital convolution.—"Étage inférieur."
13. Corpus striatum.
14. Posterior edge of corpus callosum.
15. Fornix.
16. Internal occipital fissure.
17. "Scissure des hippocampes."
18. Third cornu of lateral ventricle.
19. Hippocampus minor; a. Anterior lobes. b. Middle temporo-sphenoidal lobe. c. Cerebellum. d. Occipital lobes. e. Medulla oblongata. f. Fissure of Sylvius. g. Pons.
* ↑ Histoire Naturelle, tom xiv., p. 61. Paris, 1766.
* ↑ Icones, Cor. xxxii, p. 54.
* ↑ "Bei der Messung der Lange des Balkens muss man wohl im Auge behalten dass man ihn Misst so lange die Hemisphären ihre Lage noch in Schädel haben; am herausgenommenen Gehirn dehnt er sich sehr betractlich in die Lange aus und verliert seine Wolbung." Huschke. Schaedel, Him und Seele, p. 110.
* ↑ Gratiolet, Memoire sur les Plis Cerebraux. Planche iv., fig. 1 and 2.
* ↑ Comptes Rendus, Avril, 1860, p. 803.
* ↑ Schrœder van der Kolk et Vrolik, citt. Gratiolet, Mem. p. 49, Planch vi. 5 and 6.
* ↑ Citt. ap. Wagner's Icones Zootomicæ Taf. viii., figs. 2 and 3.
* ↑ Since the above paragraphs were written, casts have been taken of the interior of the skulls of our second orang and of the chimpanzee with the following results. The cast of the orang's skull approximates more nearly to the proportions of the brain we have figured than does the prepared brain it represents; the relative extent of the space occupied by the mass corresponding to the cerebellum, being somewhat greater than that occupied by the cerebellum itself, in the specimen. Still, in such a view of the cast as that given in fig. 3 of the first of our brains, no cerebellar surface at all comes into view; though a little less cerebral surface comes out laterally than in the preserved brain in a similar view to that in fig. 2. The cast of the chimpanzee's skull represents the cerebral hemispheres as overlapping the cerebellum to a greater extent, posteriorly, than they do in the preparation, the hemispheres having in this, as in certain figured preparations, fallen apart laterally somewhat, and lost thus in antero-posterior, what they have gained in lateral, extent.
* ↑ Hunterian Osteological Catalogue, 5346, 5755. See, also, Symbolik der Menschlichen Gestalt., von. C. G. Carus, p. 170, fig. 34.
* ↑ Schaedal Hirn und Seele. 1854, p. 112.
* ↑ Huschke, l. c, p. 60.
* ↑ Tiedemann, citt. Huschke, p. 73.
* ↑ Quain's Anatomy, by Sharpey and Elite, vol. ii., 433, note. 1856.
* ↑ Schrœder van der Kolk et Vrolik, citt. Nat. Hist. Review, No. 1., p. 80.
* ↑ Schrœder van der Kolk? citt. Huschke, l c., p.82.
* ↑ Idem, Ibid., p. 129.
* ↑ Schrœder van der Kolk ap. Huschke, p. 129.
* ↑ Gratiolet, Memoire, p. 54.
* ↑ Nat. Hist. Rev., i., p. 83.
* ↑ Memoire, pp. 51, 62.
* ↑ Tiedemann ap. Wagner, Icones Zoot., Taf. viii., figs. 2 and 3.
* ↑ Vorstudien zu einer Wissenschaftlichen Morphologie und Physiologie des Menschlichen Gehirns als Seelenorgan. Von Rudolph Wagner. Gottingen. 1860.
* ↑ Wagner, Icones Zoot., viii., 3.
* ↑ Ap. Wagner, Icon., taf. viii., fig. 2.
* ↑ Gratiolet, Memoire, p. 78.
* ↑ Ibid., p. 76.
* ↑ Ibid., P. 60.
* ↑ Memoire, l. c.
* ↑ Nat. Hist. Rev., l. c., p. 79.
* ↑ Icones, p. 51.
* ↑ Icones, p. 51.
​Fig. 1.
| Fig. 2. | Fig. 3. |
Fig. 4.