Evolution and the Darwinian theory of human descent viewed from the standpoint of a multiple primate ancestry by Charles K. Mills : papers and discussion of the paper by Dr. Mills / Dr. Francis X. Dercum, Dr. William B. Cadwalader, Dr. J. Hendrie Lloyd and Dr. J. Parsons Schaeffer.

  • Mills, Charles K. (Charles Karsner), 1845-1931
Date:
[1928]
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Licence: In copyright

Credit: Evolution and the Darwinian theory of human descent viewed from the standpoint of a multiple primate ancestry by Charles K. Mills : papers and discussion of the paper by Dr. Mills / Dr. Francis X. Dercum, Dr. William B. Cadwalader, Dr. J. Hendrie Lloyd and Dr. J. Parsons Schaeffer. Source: Wellcome Collection.

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    dicular fissure as preferable to the term sulcus lunatus employed by Elliot Smith. The name “Affenspalte” (ape cleft) employed by some of the German writers is significant. It is also known in the human brain as Wernicke’s fissure. A close relationship between the occipital lobe and the parietal lobe seems to have been the direct result of the change from the quadrupedal to the bipedal attitude. The more that progression became relegated to the posterior or lower extremities the more did the anterior or upper extremities, the arms and hands, become free to grasp, to handle and to examine objects. In the occipital lobes reside not only the function of vision but also such cognate func¬ tions as the perception of perspective, of distance, of depth and of the relations of objects in the field of vision to each other. These functions reside in what may be called the visual association areas, whose correct functioning depends on motor centers situated elsewhere, which we need not now consider. Obviously, when an ape form progressed to such an extent that its upper extremities, its hands, were left free to examine objects tactually and to note size, weight, smoothness, roughness, hardness, softness and the other qualities that make up stereognostic perception, it examined the object at the same time with its eyes, and the stimulation of the interplay between the parietal lobe with its great tactual association area and the occipital lobe led to a closer morphtdogic relationship and to the development of such bridging convolu¬ tions as the pli de passage superieure externe. The failure of a brain to develop the pli de passage superieure externe is justly to be regarded as an evidence of a developmental failure and therefore of a low type brain. Together with peculiarities of like significance, it was especially pronounced in the brain of one of the murderers that I examined. The change to the erect posture appears also to have been accompanied by a lessened necessity for the presence of another pli de passage; namely, the pli de passage inferieure interne. This pli de passage allows a free interchange between the mesial surface of the occipital lobe and the callosomarginal gyrus, but in man it has become submerged or is altogether absent. Time will not permit my dealing with this point in detail, but the fact is so interesting that I cannot refrain from alluding to it. Normally, the parieto¬ occipital fissure terminates in the calcarine fissure. In an examination of thirty-three brains of negroes, made by A. J. Parker, he discovered two instances in which a confluence did not occur between these fissures. They were separated by a well developed convolution; this convolution Gratiolet termed the pli de passage inferieure interne. In the apes this convolution is constant except in Hylobates and Ateles, but it is almost uniformly absent in the human brain. (The submergence or loss of the pli de passage inferieure interne in the case of such widely separated forms as the gibbon, an Asiatic anthropoid, and the spider monkey, a South American primate, may fairly well be regarded as an instance of “parallel evolution.” It is of extraordinary interest, however, to note that the extreme length of the arms in both forms spontaneously brings about an erect position.) The finding of this convolution in two instances in the brain of the negro is therefore highly significant. In the white brain it was found by Dr. Mills in only one instance, and that was in the case of a murderer. Benedikt of Vienna had also described the brain of a criminal in which the calcarine was separated from the parieto-occipital and put on record also a similar condition which he found in a Chinese brain. I had the privilege of going over the collection of brains of idiots made by Dr. Wilmarth of the Elwyn Institution for Feebleminded Children. Among seventy-five brains, I found four instances of the presence of such a pli de passage. Two of these existed in opposite hemispheres of the same brain. In both instances the convolution was large and well developed. In addition, it was twice found (in the same brain) barely submerged. All of these brains in which the convolution occurred were those of white low grade idiots. The presence of a pli de passage inferieure interne is therefore beyond all doubt evidence of a low type brain.