796 KEPOKT— 1908. 



however, distinct limitations in the degree to which the various cerehral fissures 

 and convolutions impress tlie 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, cannot 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 centres have to rely mainly upon certain 

 linear and angular measurements made from points frequently remote from these 

 centres. 



The cranium is not merely a box developed for the support and protection of 

 the brain, and more or less accurately moulded in conformity with the growth of 

 this organ. Its antero-lateral portions aftbrd 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 ofraastication — muscles, jaws, and teeth. There is strong 

 evidence in favour of the view that the evolution of man from microcephaly to 

 macrocephaly has been associated with the passage from a macrodontic to a 

 microdontic condition. The modifications in the form of the cranium due to the 

 influence of the organs of mastication have been exerted almost entirely upon its 

 external table ; hence external measurements of the cranium, as guides to the shape 

 of the cranial cavit}^ and indications of brain development, while fairly reliable 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 dolicho- 

 cephalic nor braciiycephalic. These measurements are expressed by an index in 

 which the langth is taken as 100. If the proportion of breadth to length is eighty 

 or upwards, the skull isbrachycephalic ; if between seventy-five and eighty, mesati- 

 cephalic ; and below seventy-five, dolichocephalic. Such a measurement is not so 

 simple a matter as it might appear at first sight, and craniologists may themselves 

 be classified into groups according as tbey have selected the nasion, or depression 

 at the root of the nose, the glabella, or prominence above this depression, and the 

 ophryoii, 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 three points was chosen, and each point would be about 

 the same distance from tlie brain. With the appearance of the teeth of the second 

 dentition and the enlargement of the jaws the frontal bone in the region of the 

 eyebrows and just above the root of the nose thickens, and its outer table bulges 

 forwards so that it is now no longer parallel with the inner table. 15etween these 

 tables air cavities gradually extend from the nose, forming the frontal sinuses. 

 Although the existence and significance of these spaces and their influence on the 

 lirominence of the eyebrows were the subject of a fierce controversy more than 

 half a century ago between the phrenologists and their opponents, it is only 

 recently that their variations have been carefully investigated. 



The frontal sinuses are usually supposed to vary according to the depree of 

 prominence of the glabella and the supra-orbital arches. This, however, is not the 

 case. Thus Schwalbe ' has figured a skull in which the sinuses do not project as 

 high as the top of the glabella and supra-orbital prominences, and another in which 

 tbey extend considerably above these projections. Further, Dr. Logan Turner,'^ 

 who has made an extensive investigation into these cavities, has shown that in the 

 aboriginal Australian, in which this region of the skull is unusually prominent, the 

 frontal sinuses are frequently either absent or rudimentary. The ophryon has 



' 'Studien iiber Pithecanthropus erectus,' 2eitsclmft far Mor2>'hologie mid Anthros 

 2>olo!)u', Bd. i. 1899. 



' 2%e jipcessp'ry Sinuies of the Nose, 190J, 



