1905-] THE OCCIPITAL CONDYLES. 9 



separated groups of races when classified according to cephalic, 

 orbital and other indices. The face as a whole is capable of 

 being largely modified by habit and environment, probably to a 

 much greater extent than has been recognised. The result no 

 doubt tends to reduce prognathism and simultaneously to reduce 

 the weight of the facial bones; and as a consequence the per- 

 manent position of the skull upon the vertebral column is 

 attained, while the occipital condyles are relatively nearer to the 

 frontal end of the glabello-occipital diameter. At the same time 

 the basi-nasal diameter is shortened. 



On the other hand, large and povverful prognathic jaws are 

 associated with a longer basi-nasal diameter; the anterior part 

 of the cranial floor or base becomes correspondingly elongated; 

 the brain is permitted to extend more freely forwards; the 

 supra-inial portion of the occipital bone becomes tilted forwards, 

 and the occipital condyles thus appear relatively drawn back- 

 wards, so as entirely to change their position relative to the præ- 

 and post-condyloid segments of the glabello-occipital diameter. 



In support of these statements I may add that the average 

 basi-nasal length of twelve dolichocephalic skulls of Aboriginal 

 Australians was 104.9 mm. while the average length of the same 

 diameter in fourteen dolichocephalic Scandinavian skulls was 

 only 101 mm. Again the average basi-nasal length of nine 

 brachycephalic Sandwich Island skulls was 104.5 mm. while five 

 brachycephalic Scandinavian skulls gave an average of 96.6 mm. 

 From such figures it is quite evident that the floor of the skull 

 anterior to the basion may present decided differences, although 

 the skulls provide similar cephalic indices. This seems to prove 

 that there are structural facts connected with the base of the 

 skull which are neither dependent upon the cerebral proportions 

 nor upon the attitude, but which result simply from the evolution 

 of the Face. 



The extremely rudimentary condition of the facial bones in 

 a fcetus or new-born infant is therefore without doubt the 

 direct cause of the long and characteristic postcondyloid seg- 

 ment and of the correspondingly short præcondyloid segment. 



