206 L. W. G. Bijckner: 



(■i) Broca's occipital angle. (See fig. 2.) The angle i.s cun- 

 tinued by the nasion-basion, and basion-opisthion 

 planes. 



(5) The foraininal angle l)ased on the Frankfort plane. (See 



fig. 2.) 



(6) The nasion-inion length. 



(7) The basal index. (See fig. 2.) 



(8) The basal angle. (See fig. 2.) 



Of the above observations, numbers 1 and 2 were estiniateci 

 <iirectly on the skull by Professor Berry and Dr. Robertson in 1909, 

 and for permission to utilise these figures I have to express my 

 thanks to these authors. Number 6 has also been recorded else- 

 where/ by the present writer. The remainder of the observa- 

 tions are the original contribution of the present work, and for 

 Avhich I. am responsible. 



For determining the position and slope of the foramen occipitale 

 magnum, I have employed three distinct methods. 



Of these, the first is Broca's Avell-known occipital angle, the 

 second is determined by utilising the Frankfort Plane as a base 

 line, and the third is the original method of the present work, and 

 is based on the nasion-inion plane. 



As Broca's method is so well known, and has already been 

 referred to, there is no necessity for any further explanation con- 

 •cerning it. 



For the second method I have utilised the Frankfort plane as a 

 base line. Bolk has referred to the fact that Hubert also determined 

 the slope of the foramen by using this plane 6n non-bise<ted skulls. 

 Bolk further states that he considers it to be a method wliich is 

 preferable to others when the skull ci^nnot be bisected. Unfortu- 

 nately, this work is not available in Mell)ourne, nor is any abstract 

 of it available. The method which I propose to use, therefore, may 

 •or may not be original. In any case, whatever observations are 

 based on the Frankfort plane, will only give the inclination of the 

 slope of the forameti, and not its position and situation (Hi tlie 

 .skull base. The method I have adojjted is to project a lino down- 

 wards at right angles to the Fraiikfort plane, and cutting the 

 basion. The angle which this line makes with the l)asi()ii(i)>isthi(in 

 plane determines the foramina! angle (see fig. 2). 



As J{olk also points out, the inaccuracy which ni'conipanics tlie 

 ■estinuition of angular measurement by direct observation is lessened 

 by constructing pi'ojections on a suitable base line. He says, 

 ■" The ])osition of every point in the skull varies (ni its own 



