A CONTRIBUTION TO THE STUDY OF THE SCOTTISH SKULL. 



445 



From this he draws a line to the point on the inner surface of the occipital bone 

 furthest removed from the Fronton, which he names the " Occipiton." If there is an 

 arc equidistant from the Fronton he makes the Occipiton the centre point of the arc. 

 This Fronton-Occipiton line (FO) is his base line, and from the basion, the middle point 

 of the anterior margin of the foramen magnum, he drops a perpendicular on the 

 line FO, meeting it at R, then the length FR divided by the length FO and multiplied 

 by 100 gives him an index which defines the position of the basion and thus of the 

 foramen magnum. To measure the degree of inclination of the plane of the foramen 

 magnum he joins the point B to opisthion S, and the size of the angle at B 

 formed by the lines BR and BS is a measure of the slope of the plane of the 

 foramen magnum. 



I have followed the above procedure in regard to the 98 skulls in the series, and 

 find that the index described above or the "basal index" (Bolk) ranges from 39"5 to 

 51 '5, with a mean value of 45 '61, which points to the fact that, as a rule, the anterior 

 limit of the foramen magnum is in front of the middle of the Fronton-Occipiton line ; 

 in fact, there are in the series only two skulls with an index above 50. 



Bolk's important conclusion from the investigation of a large number of specimens 

 is " that in man, as the anthropoids, the foramen magnum is shifted occipitally during 

 development." He gives values for the index of position of the foramen magnum, or 

 index basalis as he names it, and it is interesting to compare these values with those 

 obtained by me in the Scottish series : — 



Table LII. 



Race. 



Index. 



Type of Skull. 



Zeelandians . 



Javanese 



Papuans 



Frisians 



Negroes 



Scottish 



45-7 

 47-9 

 44-6 

 44-7 

 466 

 45-61 



• 



Brachycephalic 



Dolichocephalic 

 Mesaticephalic 

 Dolichocephalic 

 >> 



The Scottish mean index is thus seen to be about equal to that shown by the 

 Zeelandian specimens, slightly greater than that shown by the Papuans and Frisians, 

 and less than that shown by the Negro and Javanese skulls. In the case of the 

 Negro group the range of the index is from 42 to 50 ; in the Scottish it is from 39 '5 

 to 51 '5 ; so that specimens may be found in the Scottish series with the foramen 

 relatively further back than in the Negro, although on the average the opening lies 

 relatively further forward in the former than in the latter. 



According to Bolk there is "no definite relation between the position of the 

 foramen magnum and the shape of the skull," i.e. the cephalic and basal indices 

 are independent of one another. 



