A CONTRIBUTION TO THE STUDY OF THE SCOTTISH SKULL. 421 



the use of any base line adopted, and the present state of opinion as regards this may 

 be summed in the words of Cleland regarding the choice of a base line, " All planes 

 are arbitrary ; if any be true, they have not been proved to be so." 



One of Klaatsch's reasons for the adoption of the glabella-lambda line as a base 

 was that it corresponded with the natural position of the head during life, but 

 Cleland (15) came to the conclusion that "it is quite likely that it will always 

 remain impossible to determine from the characters of a skull what was its precise 

 position in the erect posture of the body." The respective variability shown by the 

 various lines drawn from the basion to the nasion, glabella, and prosphenion show that 

 in a uniform series like the present one the variability of development of the glabella 

 is practically negligible. 



Turner (47) adopted the nasi-tentorial line as abase line, as he believed the nasion 

 was a more suitable point than the glabella to be the anterior extremity of a line 

 drawn to estimate the length of the cerebral portion of the cranial cavity. Keith (25) 

 takes a somewhat similar plane, which he names the " sub-cerebral." Bolk (42), 

 dissatisfied with all other base lines, adopted still another, called the " Fronton- 

 Occipiton" line, which is drawn from the "Fronton," a point on the inner surface 

 of the anterior cranial wall in the middle line where this becomes continuous with 

 the floor of the anterior cranial fossa to the " Occipiton," the point on the inner 

 aspect of the posterior cranial wall furthest removed from the " Fronton." If there 

 was an arc equidistant from the " Fronton," the centre point of the arc was taken 

 as the " Occipiton." 



In my study of the sectionised skull I have made use of Bolk's line, and have also 

 drawn in the nasi-tentorial line to give me the nasi-tentorial plane. I have calculated 

 the coefficients of variation of these two lines, and find that of the two the nasi- 

 tentorial line is slightly the more variable, while both are distinctly more variable 

 than the glabella-occipital and even than the glabella-lambda length, but slightly 

 less variable than the glabella-inion line (the magnitude of the coefficient of variation 

 being taken as the index of variability). 



In a uniform series of skulls like the present one, therefore, the variability of the 

 prominence of the glabella may be considered as practically negligible in regard to 

 any influence on the length of a line drawn from it to another point on the skull, 

 but of course in a heterogeneous collection of skulls, or in comparing skulls of 

 different races, the influence of its variable development would probably be more 

 marked. It is an interesting fact, however, that even in such a homogeneous 

 series of skulls the basion-lambda line should show the smallest coefficient of 

 variability. 



With regard to the lambda-inion chord, this is the most variable of all the chords 

 measured so far. In the Tasmanian series the length varies from 47 to 73 mm., with 

 a mean length of 5 6 '7 mm. ; the S.D..is 7 '04 and V. is 12 "4. In Turner's Tasmanian 

 series of 6 the mean value is 56 mm., while in the Scottish series the corresponding 



