24 Proceediiigs of the Royal Physical Society. 



ately, i.e., independently. Among civilised races, all forms of 

 skull are found, and even within the same race examples of 

 the extreme types occur. Whether or not this should be attri- 

 buted to intermingling, due to parentage possessed of opposite 

 types of skull, or to the results of reversion, i.e., historical 

 repetition, are open questions. We cannot, however, entirely 

 ignore the fact that the cranium is, after all, merely a case 

 for the brain, whose growth must certainly influence the 

 dimensions of its case. Further, it is the proportion between 

 the length and the breadth of the cranium which stamps a 

 skull as dolicho-cephalic or brachy-cephalic. 



As regards lower animals and primitive human races, it 

 may quite well be the custom for brain growth, and the 

 closure of cranial sutures, to proceed on lines sufficiently 

 constant to result in crania of types to correspond. Since, 

 however, among higher races all types of cranium occur, we 

 may reason that variation in the periods at which cranial 

 sutures become obliterated around a growing brain, may be 

 the main cause of that variation in relative proportions which 

 determines the type of any particular skull. While we have 

 considerable knowledge concerning the periods and sequence 

 of the obliteration of cranial sutures among civilised races, 

 our similar knowledge concerning primitive races and animals 

 is imperfect, and, moreover, we cannot be said to know very 

 much regarding the relative rates of growth of different parts 

 of the brain. 



The rate at which any particular mass of the brain grows, 

 and the period at which it shows greatest activity, must pro- 

 duce some influence upon the dimensions and shape of an 

 osseo-membranous encasing, and in this association we may 

 find much of the information required to account for funda- 

 mental types of skull among primitive races. 



If we may argue from the fact that deformities of the skull 

 produced artificially during infancy do not seem to give rise 

 to interference with the quality and functions of the con- 

 tained brain, we may assume that the actual shape and 

 proportions of the skull are of minor importance. Conse- 

 quently, variations in the sequence of the closure of the 

 cranial sutures, although they result in variations of cranial 



