PECTORALIS MAJOR AND DELTOID INSERTION 167 



considerably less, than the variability of the position index of the 

 pectoralis major, the variation of which equaled 49 per cent of 

 its mean. The last named index shows in every group a greater 

 variation coefficient than the corresponding ones in table 6. 

 Therefore the deltoid possesses a more constant position of in- 

 sertion than the pectoralis major muscle. Judging from the 

 averages of the position index the attachment of the deltoid mus- 

 cle must be relatively slightly more distal in the males of the 

 white race, and slightly more proximal in the males of the ne- 

 groes than in the females of either. There is no difference in the 

 two races in the position of the insertion of the deltoid, similar 

 to that found to be the case for the pectoralis major. The rela- 

 tive position of the deltoid insertion is also almost regularly un- 

 equal on both sides; more frequentl}^ the muscle is more proxi- 

 mally situated on the right side. In all the groups the averages 

 of the position index of the deltoid are on the right — in part 

 even considerably — smaller than those of the left side. A rela- 

 tionship between the strength of the deltoid muscle and its in- 

 sertion position does not exist. The question as to what extent 

 the positions of the insertions of the pectoralis major and the 

 deltoid may change correspondingly is best answered by the 

 following tabulation of the correlation coefficients with their 

 probable errors for the two indices of position which have been 

 previously used. White males + 0.52 ± 0.057, white females 

 -f 0.37 ± 0.123, negro males + 0.29 ± 0.071, negro females 

 + 0.70 ± 0.061. The coefficients, which are regularly positive, 

 indicate that a shifting of one of the muscles is usually followed 

 by a change to a greater or less extent of position of the other 

 muscle in the same direction. This is very noticeable in female 

 negroes and in male whites. In the material used the proximal 

 point of measurement of the insertion of the deltoid was found 

 above the distal point of measurement of the pectoralis major 

 muscle insertion in one hundred and eighty-six cases; sixteen 

 times t'le points referred to were at the same height and in only 

 eight cases was the first point found below the latter. 



The most proximal region of insertion of the deltoid is much 

 more variable than the most distal. In order to free the index 



