TRANSACTIONS OF SECTION H. 793 



resistance offered by its coverings, and there are certainly stages when tlie brain 

 does not fully occupy the cranial cavity. 



At an early period in the pliylogeny of the vertebrate slvull the structure of the 

 greater part of the cranial wall changes from membranous tissue into cartilage, the 

 portion persisting as membrane being situated near the m.'dian dorsal line. In 

 the higher vertebrates the rapid and early expansion of the dorsal part of the fore- 

 brain is so marked that the cartilaginous growth fails to keep pace with it, and 

 more and more of the dorsal wall of the cranium remains niemljrauous, and subse- 

 quently ossities to form membrane bones. Cartilage, though constituting a firmer 

 support to the brain than membrane, does not possess the same capacity of rapid 

 growth and expansion. The head of a young child is relatively large, and its skull 

 is distinguished from that of an adult by the small size of the cartilaginous base of 

 the cranium as compared with the membranous vault. The appearance of top- 

 lieavmess in the young skull is gradually obliterated as age advances by the carti- 

 lage continuing slowly to grow after the vault has practically ceased to enlarge. 

 These changes in the shape of the cranium are associated "with corresponding 

 alterations in that of the brain, and it appears to me that we have here an illustra- 

 tion of how the conditions of skull growth may modify the general form of the 

 brain. 



Whatever may be the precise influences that determine skull and brain growth, 

 there can be no doubt biit that within certain limits the external form"" of the 

 cranium serves as a reliable guide to the shape of the brain. Statements such as 

 those by Dr. J. Deniker,' 'that the inequalities of the external table of the cranial 

 walls have no relation whatever with the irregularities of the inner table, and still 

 less have anything in common with the configuration of the various parts of the 

 brain,' are of too general and sweeping a character. Indeed, various observers 

 have drawn attention to the {act that in certain regions the outer surface of the 

 skull possesses elevations and depressions which closely correspond to definite 

 fissures and convolutions of the brain. Many years ago Sir AVilliam Turner, who 

 was a pioneer in cranio-cerebral topography, found that the prominence on the 

 outer surface of the parietal bone, known to anatomists as the parietal eminence, 

 was situated directly superficial to a convolution of the parietal lobe oF the brain, 

 which he consequently very appropriately named.' the convolution of the parietal 

 eminence.' Quite recently I'rofessor G. Schwalbe has shown that the position of 

 the third or inferior frontal convolution is indicated by a prominence on the sur- 

 face of the cranium in the anterior part of the temple. This area of the brain is of 

 special interest to all students of cerebral anatomvand physiology, since it was the 

 discovery by the illustrious French anthropologist and physician, M. Broca, that 

 the lef*} inferior frontal convolution was the centre for speech, that laid the scien- 

 tific foundation of our present knowledge of localisation of function in the cerebral 

 cortex. This convolution is well known to be much more highly developed in man 

 than m the anthropoid apes, and the presence of a human cranial speech-bump is 

 usually easily demonstrated. The faculty of speech, however, is such a compli- 

 cated cerebral function that I would warn the ' new ' phrenologist to be cautiou.s 

 in estimating the loquacity of his friends bv the degree of prominence of this part 

 of the skull, more particularly as there are other and more reliable methods of 

 observation by which he can estimate this capacity. 



In addition to the prominences on the outer surface of the cranium, corresponding 

 to the convolutions of the parietal eminence and the left inferior frontal convolu- 

 tion, the majority of skulls possess a shallow groove marking the position of the 

 Sylvian point and the course of the horizontal hmb of the Sylvian fissure. Below 

 these two other shallow oblique grooves indicate the line of the cerebral fissures 

 which divide the outer surface of the temporal lobe into its three convolutions, 

 termed superior, middle, and inferior. Most of tliese cranial surface markings are 

 partially obscured in the living body by the temporal muscle, but they are of 

 interest as showing that in certain places there is a close correspondence in form 

 b.etvye.en the external surface of the brain and that of the sknU. There are, 



' Tftfi Haces of Man, p. 53. 



