( 2 ) 



taken that the point does not slip off the glabella. The point of 

 maximum length at the back of the head will usually be found 

 nearly in the same plane with the glabella. In searching for it, 

 the posterior point of the cephalometer must be kept moving up and 

 down in the central perpendicular line of the back of the head, and 

 the graduated scale of the instrument must be watched so as to see 

 when the maximum diameter has been reached. The inion or 

 occipital protuberance is not the point to be measured to. A magni- 

 fier may be used to read the scale of the cephalometer, which is 

 graduated rather minutely. After having found the maximum, the 

 measurer should take care not to remove the instrument from the 

 subject's head before reading off the measurement, or if he does so, 

 should tighten the screw. Experience shows that it is very difficult 

 to remove the instrument without altering the reading, unless the 

 screw has been tightened. 



The maximum transverse diameter (B in Fig. 1) is best measured 

 from behind the subject. Its terminal points will usually be found 

 somewhere near B. There is no special difficulty in measuring 



it. All that 

 the operator 

 has to do is 

 to watch the 

 graduation 

 of the ce- 

 phalometer, 

 so as to see 

 when he has 

 hit upon the 

 maximum 

 diameter. 

 He must 

 also see that 

 the branch- 

 es of the 

 instrument 

 on either 

 side are in 

 the same 

 plane. Vide 

 figures 2 

 and 3. 

 In measuring the zygomata (posterior arches of cheek-bones) 

 care must be taken to hold the instrument steady, as the points are 

 apt to slip off the ridges of bone on one side or other, and thus to 

 record too small a dimension. The measurement is the maximum 

 breadth procurable with the cephalometer at the points F — F in 

 figure 4. The index is formed with the bigoniac breadth E — E 



E— E x 100 

 thus - ^_ F ■ 



Fig. 2.— Anteroposte- 

 rior diameter. 



Fig. 3. — Transverse 

 diameter. 



