47 



unsymmetiy varies, it is probable that no such thing as a 

 perfectly symmetrical human skull exists. 



As to orthognathism and prognathism, it may be observed 

 that Retzius includes amongst the orthognathi the Celtic 

 Scotch, Irish, and Welsh. Any one who has travelled 

 amongst these peoples would be able to confute the uni- 

 versal, or even general, truth of this statement. Amongst 

 the lower Irish, indeed, prognathism is the prevailing type, 

 and there is this further interest about the subject, that 

 prognathism appears to be a type rapidly acquired by 

 changed external circumstances. The conclusions arrived 

 at are as follows : — 



It is probable that when the struggle for existence was 

 less keen than it is at present, and the human brain was in 

 consequence less prone to rapid growth, human skulls pre- 

 served a pretty uniform tj^pe, thus, e.g., all the neolothic 

 skulls yet found are dolicocephalic, and what is also worth 

 noting, they are of an unusually symmetrical character. It 

 is in accordance with the doctrine of evolution to suppose 

 that different environments (such as differences in climates, 

 soil, mode of livelihood, e.g., living by the chase or by agri- 

 culture) would produce certain and definite cranial changes : 

 hence would arise national types of skulls, slow in arriving 

 at such a difference as exists between the Eskimo and the 

 Negro, and slow in changing that type when acquired. 

 After a time the influence of civilization would come into 

 operation, which would tend to produce varieties in the 

 crania of a nation in accordance with the varieties of the 

 environments of the individuals comprising the nation. A 

 similarity of external circumstances and an absence of 

 intermarriage would tend to produce but one type of 

 skull, a difference in external circumstances and inter- 

 marriage would tend to produce a varying type. These 

 factors are both at work in civilized countries. Nations 

 whose skulls have long ago been of a well-marked distinctive 

 character are exposed to the same environments and inter- 

 marry — the result is a confusion and mingling of the 

 different forms. 



