10 DAVID HEPBURN. [No. 3. 



As a result of these observations I am forced to the 



following conclusions: 



Ist. The occipital condyles are developed upon the base of the 

 fætal skull relatively much farther forward than has been 

 supposed; 



2nd. They attain their adult position by a relative transposition 

 in the backward or occipital direction owing to an increase 

 in the basi-nasal diameter whereby the vault of the skull 

 is rotated forwards, and not by a backward rotation of the 

 vault with consequent increase of the occipital section of 

 the floor of the skull and apparent movement of the con- 

 dyles from behind forwards; 



3rd. As the basi-nasal diameter increases, the cerebrum is rotated 

 or tilted forwards, and the cerebellar region undergoes 

 enlargement; 



4th. These changes in the proportion of the præcondyloid and 

 postcondyloid segments are not due to any special necessity 

 for ensuring a balance of the skull upon the vertebral 

 column, since this is a result, rather than a cause, of the 

 changes ; 



5th. The chief determining causes are facial growth and enlarge- 

 ment, which in their turn are due to environment and habit 

 reacting upon each other so as to produce different facial 

 characters; 



6th, Large basi-nasal diameters may equally be associated with 

 both dolichocephaly and brachycephaly, as is shown by the 

 averages recorded, viz. Aboriginal Australians 104.9 mm. 

 and Sandwich Islanders 104.5 mm., notwithstanding the 

 fact that the average gnathic indices for the skulls quoted 

 were respectively 101 and 97; 



7th. While the size and proportion of the face affect the basi- 

 nasal diameter, the amount of the præcondyloid segment 

 and the gnathic index, they do not necessarily influence 

 the cephalic index; 



Sth. Prominence should be given to the percentage amount of the 

 præcondyloid segment as a check upon the cephalic index. 



