Fijraineii Occipifah' M(i(/ini.ia. liUT 



iiL'connt, since un every imint a liii'^e luinilKr i>t' factors have a 

 localising influence." Twi. of these points may have a nurnljer of 

 factors in conniion. Thcii'luiH', if in two skulls tlic angle hounded 

 hy these points is found to vai-y, this diffcii'mc is not to Ije 

 accounted foi- hy the shifting of one point oidy. 1 have, therefore, 

 estimated the inclination of the slope of the foramen in the manner 

 just descrihed. 



Tlie thii-d method of determining hotli the jiosition and slope 

 <)f tlie forajiif'/i is a modification of that desciihed by JJolk. save 

 that the base lines are <lift'enMit. The base line which 1 propose to 

 use in the nasion-inion phuie. It has been pointed out ]>y Schwalhe.^ 

 Cunningham, 7 Berry and Robertson. 8 as well as myself,^ that this 

 plane is an important one in iom})arative craniology. The several 

 observations recorded by the above investigators all serve to support 

 this contention. Another reason — and a strong one — is. tliat in 

 Beri-y and Robertson's Atlas of Tracings of Tasmanian crania? the 

 necessary points are accurately denoted, so that observations may 

 be estimated direct from the tracings in the median sagittal plane. 

 My reasons for utilising this plane as a base line Avould. theiefore, 

 appear to be quite valid. 



For the determination of the position and slojie of the foramen, 

 by adopting the procedure already recorded when describing Bolk's 

 method, I have constructed a basal index, and a basal angle. As 

 before a line is dropped at right angles from the base-line — in this 

 case the nasion-inion plane — and cutting the basion (see fig. 2). 

 The basal index is then calculated by taking the ratio, which XX 

 bears to X^I, the latter being referred to as 100. 



P>asal Index NX x 100 



Nl 



The Basal Angle is likewise determined by estimating the angle 

 which is contained by the two planes, X Ba and 15a Op (see tig. 2). 

 As the method is adopted from Bolk's work, any further explana- 

 tion is deemed unnecessary. 



The material on which the present j)a])er is I)ased will hi' found in 

 Berry and Robertson's Atlas of Tracings of Fifty-two Tasmanian 

 Crania. All the observations recorded in tabU' 1., with thi' excep- 

 tion of the two already referred to. namely, the length and breadth 

 of the foramen, have been estimated direct from the tracings in the 

 median sagittal plane; that is, in the nor/no //ifrralis. As numbei 

 48 has previously been shown to be that of a juvenile, all the 

 observations recorded on it have been omitted from the table of 

 generalised results. 



