550 



SCIENCE. 



[N. S. Vol. XVIII. No. 461. 



outer surface of the cranium, correspond- 

 ing to the convolutions of the parietal 

 eminence and the left inferior frontal con- 

 volution, the majority of skulls possess a 

 shallow groove marking the position of the 

 Sylvian point and the course of the hori- 

 zontal limb of the Sylvian fissure. Below 

 these, two other shallow oblique grooves in- 

 dicate 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 

 these 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 corre- 

 spondence in form betAveen the external 

 surface of the brain and that of the skull. 

 There are, however, distinct limitations in 

 the degree to which the various cerebral 

 fissures and convolutions impress the inner 

 surface of the cranial wall, or are repre- 

 sented 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 the 

 surgeons in planning the seats of opera- 

 tions necessary to expose the various motor 

 centers have to rely mainly upon certain 

 linear and angular measurements made 

 from points freqiiently remote from these 

 centers. 



The cranium is not merely a box de- 

 veloped for the support and protection of 

 the brain, and more or less accurately 

 molded in conformity with the growth of 

 this organ. Its antero-lateral portions 

 afford attachments to the muscles of masti- 

 cation and support the jaws and teeth, 

 while its posterior part is liable to vary 



according to the degree of development of 

 the muscles of the nape of the neck. Next 

 to the brain the most important factor in 

 determining cranial form is the condition 

 of the organs of mastication— muscles, jaws 

 and teeth. There is strong evidence in 

 favor of the view that the evolution of 

 man from microcephaly to macrocephaly 

 has been associated with the passages from 

 macrodontic to a microdontic condition. 

 The modifications in the form of the cra- 

 nium due to the influence of the organs of 

 mastication have been exerted almost en- 

 tirely upon its external table ; hence ex- 

 ternal measurements of the cranium, as 

 guides to the shape of the cranial cavity 

 and indications of brain development, 

 while fairly trustworthy in the higher 

 races, become less and less so as we examine 

 the skulls of the lower races, of prehistoric 

 man and of the anthropoid apes. 



One of the most important measurements 

 of the cranium is that which determines 

 the relation between its length and breadth 

 and thus divides skulls into long or short, 

 together with an intermediate group 

 neither distinctly dolichocephalic nor 

 brachycephalic. These measurements are 

 expressed by an index in which the length 

 is taken as 100. If the proportion of 

 breadth to length is eighty or upwards, the 

 skull is brachycephalic ; if between seventy- 

 five and eighty, mesaticephalic ; and below 

 seventy-five, dolichocephalic. Such a 

 measurement is not so simple a matter as 

 it might appear at first sight, and craniol- 

 ogists may themselves be classified into 

 groups according as they have selected the 

 nasion, or depression at the root of the 

 nose, the glabella, or prominence above this 

 depression, and the ophryon, a spot just 

 above this prominence, as the anterior 

 point from which to measure the length. 

 In a young child this measurement would 

 practically be the same, whichever of these 



