THE DEVELOPMENT OF SKULL AND BRAINS. 65^ 



to loly juainly upon cortuin linear iind jin^ular niea.su ronients made 

 from points fr('([uently remote from these centers. 



The cranium is not merely a box developed for the support and pro- 

 tection of the brain, and more or less accurately molded in conformit\' 

 with the o-rowth of this organ. Its antero-lateral portions atford 

 attachments to the muscles of mastication 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 con- 

 dition of the organs of mastication — muscles, jaws, and teeth. There 

 is strong evidence in favor of the view that the evolution of man from 

 microcephah" to macrocephal}- has been associated with the passage 

 from a macrodontic to a microdontic condition. The moditications in 

 the form of the cranium due to the influence of the organs of mastica- 

 tion 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 reli- 

 able 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 brachj^cephalic. These meas- 

 urements are expressed by an index in which the length is taken as 

 100. If the proportion of breadth to length is 80 or upward, the skull 

 is brachy cephalic; if between 75 and 80, mesaticephalic; and below 

 75, dolichocephalic. Such a measurement is not so simple a matter 

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

 be classified into grou})s 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 woukl practically be the same whichever of 

 these three points was chosen, and each point would be about the same 

 distance from tiie brain. With the appearance of the teeth of the 

 second detention and the enlargement of the jaws, the frontal bone in 

 the region of the eyebrows and just above the root of the nose thick- 

 ens, and its outer table bulges forward so that it is now no longer par- 

 allel with the inner table. Between these tables air cavities gradually 

 extend from the nose, forming the frontal siiuises. Although the 

 existence and significance of these spaces and their influence on the 

 prominence of the eyebrows were the subject of a fierce controversy 

 more than half a century ago between the phrenologists and their 



