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Rh identical convolutions in different brains consist of nerve-cells with precisely the same connexions. The convoluted arrangement results from growth of brain-surface under constraint, hence as the different tracts of surface undergo proportional overgrowth they may fold along different lines. The occurrence of small differences in the rate of overgrowth, testified to by the varieties of the resulting pattern, can hardly fail to cause considerable alteration in the place of definite territories of grey cells. Some method for the determination of the limits of these shiftings of place is required before comparisons can be of value as phrenological data.

4. The comparison of the rate of growth of brain with the development of mental faculties is important not only to the phrenologist but to the psychologist. No observations on this point were made by phrenological writers, who only refer to the first and rather crude observations of the earlier anatomists. We have, however, recently learned from the researches of T. L. W. von Bischoff, Tuczec, Cunningham, and S. Exner many particulars as to the rate and progress of brain-growth. At birth the brain weighs one-tenth of the weight of the body, and averages about 11 oz. For the first year brain-growth and consequently expansion of the skull proceed with great rapidity, the growth during a large part of this period averaging one cubic centimetre daily. This enormous increase is chiefly due to the rapid development of medullated nerve-fibres, which are deficient in the foetal brain. During the second and third years growth takes place more slowly, the occipital and parietal lobes increasing more than the frontal or temporo-sphenoidal. During these and the four succeed in years the base elongates commensurately with the increasing depth of the face. In the sixth and seventh years the frontal lobes grow faster than the parietals, and at seven the average brain has attained the weight of 1340 grammes, being the weight of the body as 1:20. In the period between seven years and puberty growth is slight, but at puberty the whole brain grows actively, especially the frontal lobes. This activity lasts until about eighteen years of age, then diminishes; but the average brain does not reach its maximum size until about thirty, from a little after which period the brain tends to diminish towards senility.

5. The estimation of the relative development of grey and white matter in the several lobes is important to any theory of cerebral dynamics which allocates functions specifically diverse to each separate part of the brain-surface; but no attempt has been made by the phrenologist to obtain precise results in this direction, nor even to determine the physical constants of the two forms of brain-matter. The recently introduced method of Bourgoin and B. Danilewski, based upon the differing specific gravities of grey and white matter, promises to give definite information as to time relative amounts of these forms of brain-matter; but further experiments are needed to perfect the method.

6. The relations, if any, between the alterations which take place in the shape and position of the head and alterations in brain-surface have been speculated on by the phrenologist. Broussais is reported to have said that his organ of causality had enlarged with increasing use, and a list of cases of similar alterations of head-shape is given by Deville (Phrén. Journ. xiv. 32), most of which are simply age-changes, of the kind described by Professor J. Cleland (Phil. Trans., 1870). There are no exact measurements recorded which indicate the occurrence of topical increases of a normal brain in special directions coincident with the cultivation of definite faculties. All the so-called cases are given vaguely, with no measurements, and the careful measurements of George Combe in such cases as were available to him showed no appreciable alterations in adult heads even at long intervals of time (see also Andrew Combe, Phren. Journ. x. 414).

7. The phrenological want of knowledge of the topography of the brain-surface was necessarily correlated with ignorance of the exact relations of the convolutions to the interior of the cranial bones; these have been carefully worked out by E. Huschke, Heffler, W. A. Turner, Cunningham and Reid. Some latitude, however, must be allowed in topography, as the exact relation of convolution of skull varies with the shape of the skull. Giacomini showed that the fissure of Rolando is perceptibly farther back from the coronal suture in dolichocephalic than in brachycephalic skulls, and it is still farther back in the extreme boat-shaped form of long-headedness. Passet shows that there is a slight topographical difference in the two sexes (Arch. f. Anthrop., 1882, xiv. 89), and in the heads of those with a symmetrically-shaped skull there is often a want of lateral symmetry of convolution. Artificial deformations likewise alter the topographical relations of convolutions, and have served not a little to puzzle the phrenologist. Thus, the artificial dolichocephaly of the Caribs having bulged the squama occipitis, they decided that these people must be amiable lovers of children, &c.

8. The existence of structural differences between different areas of cerebral surface is important to any theory of cerebral localization, but no phrenologist has given us any original information on this point. Since the investigation of J. G. F. Baillarger and Bevan-Lewis it has been shown that some local differentiations of structure do really exist. Thus in the convolutions around the fissure of Rolando the ganglion-cells of the fourth layer are of large size (giant-cells of Betz), and in the convolutions of the temporo-sphenoidal lobe a layer of small angular cells (granule-cells) is interposed between the larger pyramidal and the ganglion-cells, so that, while in the parts of the brain above the fissure of Sylvius the gray cortex is for the most part five-layered, below and behind that fissure it is six-layered. There is no abrupt passage from the one to the other, the only sudden transition of structure of the grey cortex being at the hippocampal sulcus; and giant-cells, although of smaller size, and less like those of the anterior cornu of the spinal cord, are scattered over other parts of the cerebral grey matter.

Other local variations in structure have been described by Elliot Smith and other histologists.

The teaching of anatomy with regard to phrenology may be summarized thus: (1) the rate of growth of brain is concurrent with the rate of development of mental faculty; (2) there is some degree of structural differentiation as there are varying rates of development of different parts of the cerebral surface; (3) there is no accordance between the regions of Gall and Spurzheim and definite areas of cerebral surface.

Physiological Aspect.—The theory of some of the older metaphysicians, that the mind, in feeling and reflection, makes use of no material instrument is not now accepted by psychologists. It was advanced by Brougham and Jeffrey as against the theory of phrenology; but the doctrine that the brain is the organ of the mind is now universally received. While it is probable that certain molecular changes in the grey matter are antecedents or concomitants of mental phenomena, the precise nature of these processes, to what extent they take place, or how they vary among themselves have not as yet been determined experimentally; the occurrence of the change can only be demonstrated by some such coarse method as the altered pulsation of the carotid arteries, the increase of the temperature of the head, the abstraction, during brain-action, of blood from other organs as shown by the plethysmograph, or the formation of lecithin and other products of metabolism in brain-substance. As yet no light has been shed on the connexion between the molecular changes in the nerve-cell and the phenomena of thought and feeling. While our knowledge of the anatomy of the brain, especially of the grey nuclei and of the white bands uniting them, has in recent years become much more accurate (see articles and ), our knowledge of the physiology of the nerve centres is still indefinite and fragmentary, even when the utmost allowance is made for the experimental work of C. S. Sherrington, A. S. F. Grünbaum, F. Goltz and others; and the hypotheses relating to the division of labour in the nerve centres is chiefly based on anatomical structure. Certain masses of grey nerve-matter situated in the spinal cord and medulla oblongata are so linked by nerve-cords to organs outside the nervous system which are set apart for the discharge of separate functions that they obviously form parts of the mechanism for the fulfilment of such functions. In cases where these can be subjected to experiment we learn that they are nervous centres presiding over the discharge of such functions; and it has been determined by experiment, or else deduced from anatomical structure, that in those lower parts of the nervous centres which are more directly connected with the segmental elements of the body there is a certain localization of function; hence the centres of pelvic actions, of respiration, cardiac action, and inhibition of vaso-motor influence, deglutition, secretions, &c., can be mapped out in ascending series. As certain of these centres are united by bands of fibres to the larger