652 THE DEVELOPMENT OF SKULL AND BRAINS. 



outer .surface of the skull possesses elevations and depressions which 

 closely correspond to definite tissures and convolutions of the brain. 

 Many years ag'o Sir William Turner, who was a pioneer in cranio- 

 cere})ral topoo-raphy, 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 Prof. G. 

 Schwalbe has shown that the position of the third or inferior frontal 

 convolution is indicated by a prominence on the surface of the cra- 

 nium in the anterior part of the temple. This area of the brain is of 

 special interest to all students of cerebral anatomy and physiolog-y, 

 since it was the discovery by the illustrious French anthropoloo-ist 

 and physician, M. Broca, that the left inferior frontal convolution 

 was the center for speech, that laid the scientific foundation of our 

 present knowledge of localization of fimction in the cerebral cortex. 

 This convolution is well known to l)e much more hio-hly develo]3ed 

 in man than in the anthropoid apes, and the presence of a human 

 cranial speech l)ump is usually easily d(>monstrated. The faculty of 

 speech, however, is such a complicatcnl cei'cbral function that 1 would 

 warn the "new'' phrenologist to be cautious in estimating the loquac- 

 ity of his friends l)v 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 convolution, the majority of skulls possess a shal- 

 low groove marking the position of the Sylvian point and the course 

 of the horizontal limb 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 c()n\'olu- 

 tions, termed "superior," "middle," and "inferior.'' Most of these 

 cranial surface markings are partially obscured in the living body by 

 the temporal muscle, but they arc of interest as showing that in 

 certain places there is a close correspondence in form between 

 the external surface of the brain and that of the skull. There are, 

 however, distinct limitations in the degree to which the various cere- 

 bral fissures and convolutions impress the inner surface of the cranial 

 wall, or are represented by inequalities on its outer aspect. Thus 

 over the vault of the cranium the position of the fissure of Rolando 

 and the shape of the cerebral convolutions in the so-called motor area, 

 which lie in relation to this fissure, can not usually be detected from 

 a cast of the cranial .cavity, and are not indicated by depressions or 

 elevations on the surface of the skull, so that surgeons in planning the 

 seats of operations necessary to expose the various motor centers have 



