The growth of the cerebrum and cerebellum into solid bodies instead of vesicles is effected by the folding together of the primitive membrane as furrows appear upon its surface, by which it is changed into folds or convolutions, each of which (like the fold of a ruffle) may be cut out from its neighbors and opened from its inner side, like a book. It resembles a book also in the fact that it contains innumerable ideas or psychic elements, and the psychometer might read from each convolution as a book the impressions recorded in it. In its place in the brain it is like a book in a library; and as the book offers on its back a title expressive of its contents, so we label each convolution with its proper title.
In addition to the folding process, a complex growth of fibres uniting in the corpus callosum completes the solidification, but not so thoroughly as to prevent our reopening and spreading out the convolutions by exercising a little dexterity. This was a puzzle to some of the anatomists in the time of Gall, but I have found no difficulty in opening out the convolutions to the extent of five or six inches square. The cerebellum, too, though its ventricle is obliterated, is susceptible also of a manipulation, showing that it has some traces of its original formation.
From the twelve weeks embryo to those of twenty-one weeks and of seven months we trace a progressive development and a commencement of the furrows that form the convolutions.
In the brain of seven months, the right hemisphere is out open horizontally, showing the ventricle.
Thus we perceive in the essential plan of the brain its two organs, cerebrum and cerebellum, are hollow spheres which grow gradually into solid bodies, filling their interior cavities, of which the lateral ventricles in the cerebrum, which have been explained, are the remnants.
The great importance of these anatomical details arises from the fact that they show us the true central region of the brain from which its development must be determined; and although this work, designed for the general reader, cannot say much of the brain, it is necessary to show its true conformation to enable us to estimate the living brain correctly, so as to describe accurately living men, study the forms of crania, and derive some profit in ethnological studies from the forms of crania which to the ethnologists of the present time are of very little value or significance, since they neither have nor claim a knowledge of the psychic functions of the brain. I trust, therefore, my readers will not neglect these anatomical memoranda, which they will find very valuable.
I am not aware that any anatomical, physiological, or phrenological writer has given the exposition of the principles of cerebral development which I have been presenting for nearly half a century, although the anatomical facts are patent to all who choose to examine cerebral embryology, and think of what dissection reveals, instead of being thoughtlessly occupied in the mere details of dissection without rising to a comprehension of the Divine plan. Indeed, the phrenological school have positively misconceived and misstated the principles of cerebral development. We can hardly be said to have had any phrenological anatomists since the time of Gall and Spurzheim sufficiently interested in comparative human development to trace its basis in anatomy, for the able work of Solly presented the brain solely as seen by the science of dissection, and not by the science of development and psychic function.
Gall and Spurzheim, understanding cerebral structure themselves, failed to state certain principles which were necessary to guard against misconception; and they did not realize its necessity, because their methods did not include the functions of the base of the brain. Mr. George Combe, who has been the great popular exponent of their system, for which he was well qualified by his clear, philosophic mind, adopted the erroneous idea, in which he has been followed by all subsequent writers on the subject, that the cerebral organs were to be regarded as so many cones, starting from their apex at the medulla oblongata and extending to their base at the surface of the skull. Hence their development was to be estimated by measuring the distance (with a pair of callipers) from the cavity of the ear (which corresponds very nearly to the medulla oblongata) to the locations of the organs on the frontal superior and posterior surfaces of the head.
In my first study of phrenology over fifty years ago, I adopted this method, and diligently measured heads with callipers, relying on the results, until I found them decidedly erroneous. I came upon the astounding fact that the head of a prominent citizen of New Orleans, when measured in this way, indicated by the height of the upper region a character entitling him to rank among the saints, when in fact he was notorious for the unrestrained energy of his violent and vicious propensities. Engaging then in more careful study and dissection of the brain, I found why the rule was so deceptive; as the basilar region is developed below the ventricles, giving depth, while the coronal region developed above gives height, and the measurement from the ear to the top of the head included both depth and height, it might be a very large measurement from animal predominance or basilar depth alone, as it was in the case that first revealed the error of Mr. Combe.