OSTEOMETRY; THE MEASUREMENT OF THE BONES 115 



3. Divergence of the two ilia from each other. This is nothing more than 

 the sum of the previous angles as found for each side of a given pelvis, 

 and is obtained by adding the two. It could also be obtained by some 

 simple device which would measure this angle direct. 



4. Inclination angle of the pelvis as a whole. This means the in- 

 clination of the conjugata vera to the spino-symphysial plane, or to 

 the horizontal, which is the complement of the first. This angle is best 

 measured direct upon the bones by some form of goniometer, the two legs 

 resting upon the promontorium (in the median line) and the inner surface 

 of the upper edge of the pubic arch. If the girdle be held in an osteophore 

 from behind, and the vertical board used in orientation removed, the 

 aspect required is quite exposed, and readily accessible to either the 

 stationary or the clamp-on type of goniometer, by which the angle may 

 be easily measured. For some methods of measurement a steel needle, 

 fastened to the bone in such a way as to represent the conjugata vera, 

 is of assistance. 



5. Sacral inclination angle. This angle, which belongs more properly 

 under the head of measurements of the sacrum, is the inclination of the 

 sacral base to the spino-symphysial plane . The sacral base is the anterior 

 surface of the body of the first sacral vertebra, which, in a complete girdle, 

 is so closely fastened to the ilia, and intimately associated with them, that 

 it serves as a base for the entire complex. This is measured by the 

 goniometer, any form, upon a girdle properly oriented, and held in an 

 osteophore applied dorsally. The measure ment is much assisted by first 

 applying a steel needle to the surface of the base, along the median plane, 

 and firmly fastened to the bone. 



General considerations concerning angular measurements. In all 



angular measurements, both here and elsewhere, the actual obtaining 



of the values is a matter of individual ingenuity, in which there are always 



many possibilities. In general there are three kinds of methods, viz.: 



(a) direct measurement on the bone, by some sort of goniometer 



(6) charting the essential lines on paper, and measuring the angles 



thus obtained by means of a protractor 



(c) getting the essential data by linear measurements, and reckon- 

 ing the values of the angles involved by trigonometrical 

 methods. 



In many cases, where a single definite angle is receiving special at- 

 tention, and where it therefore has to be measured again and again, 

 the investigator has devised some special form of goniometer fitted to 

 this particular purpose. This is to be generally encouraged, especially 

 when the device is simple, but the modern tendency seems to be to 

 reduce, rather than multiply, the number of different instruments, and 

 to render those used more universal in their application. Thus, the 

 calipers (craniometer) of the present time, and the pelvimeter, are 

 practically identical in form, differing only in size, which is wholly a 

 matter of convenience, and both are devised for use in cases where the two 



