[17] Dr. Wilmath, of the Pennsylvania Institution for Feeble-minded, reports that in six brains the island of Reil was exposed through defective development of the 3rd frontal convolution; in four cases, on both sides; in two cases, on one side only.—Notes on the Pathology of Idiocy.
[18] Il Cervello in Relazione con i Fenomeni Psichici. Studio sulla morfologia degli emisferi cerebrali dell'uomo, Torino, 1895. P. 89.
This is a work of great merit, in which the author compares the structure of the brain of man with that of other primates; he then treats of the morphology of the brain in different races, in criminals, in the insane, in deaf mutes, and in microcephales. An extremely interesting chapter is that devoted to the assumed difference of the cerebral hemispheres in the two sexes, containing statistical tables constructed by Dr. Mingazzini himself and others. Although he mentions certain minor differences that have been noticed by different observers, he summarises his own opinion by the statement that, "from the numerous but incomplete observations upon this subject, it may be concluded with certainty that essential differences do not exist" (si può inferire quasi con certezza che differenze essenziali non esistono).
[19] Further information as to brain weight and cranial capacity, will be found in the author's treatise on "Aphasia and the Localisation of Articulate Language," chapter xii. (Prize Essay of the Academy of Medicine of France.)
[20] Op. cit., page 64.
[21] The attention of the medical profession has lately been called to the obstetric aspect of idiocy, and I would refer those who take an interest in this subject to the valuable statistics of Dr. Langdon Down, which contain the result of his inquiries into the history of 2,000 cases of idiocy that have come under his observation; from which it would seem that primogeniture plays an important part, as no less than 24 per cent. of all the idiot children observed were primiparous. The increased difficulty of parturition seemed to be an important factor. In reference to the use of the forceps in delivery as an assigned cause of idiocy, Dr. Down says, "there is no evidence that instrumental interference has any injurious influence on the mental condition of the children, but he thinks that those who delay the use of the forceps incur a much greater risk from the prolongation of pressure, resulting in suspended animation, which condition should be especially avoided. Of Dr. Down's 2,000 cases, the ratio of males to females was 2·1 to 0·9. This was probably due to the larger size of the head giving rise to the prolonged and difficult parturition, continued pressure, and suspended animation."—Obstetrical Journal, vol. iv., p. 681.
[22] Dr. Hammond, Professor of Diseases of the Nervous System at Bellevue College, New York, has published some interesting statistics in reference to the relative weight of the brain, as compared with that of the body, in various classes of vertebrate animals, by which he shows that there is no definite relation between the intelligence of animals and the absolute or relative size of the brain. Thus, he says, "the canary bird and the Arctic sparrow have brains proportionately larger than those of any other known animals, including man, and yet no one will contend that these animals stand at the top of the scale of mental development. Man, who certainly stands at the head of the class of mammals, and of all other animals, so far as mind is concerned, rarely has a brain more than one-fiftieth the weight of the body, a proportion which is much greater in several other mammals, and is, as we have seen, exceeded by many of the smaller birds."
[23] Clinical Lecture on Idiocy, p. 14.
[24] L'Encéphale, March 1881, p. 82.
[25] At a meeting of the Medico-Psychological Society of Paris, my friend M. Auguste Voisin exhibited plates of the brains of idiots who had only begun to speak at the age of from three to five years, in which the frontal and first parietal convolutions were rectilinear without secondary folds, resembling the fœtal condition of the convolutions at the sixth month of intra-uterine life.