36 THE HUMAN STERNUM 



II. THE FORM OF THE ADULT HUMAN STERNUM 



A. Length and Breadth 



The measurements of five hundred and four sterna are given in 

 Table XI — three hundred and ten male, one hundred and twenty-six female, 

 and sixty-eight unclassed. Among those whose ages where known, one 

 hundred and eighty-three were under forty, and two hundred and fifty- 

 three were over forty years of age. An analysis of the measurement shows 

 distinct differences dependent upon age and sex. 



(a) Age Differences. 



In Table XI, the male and female sterna over twenty-one years of 

 age have been grouped together in two series — under and over forty years 

 of age. From a comparison of the measurements of the two groups, it 

 appears that a certain increase, both in breadth and length, takes place after 

 the age of forty. This increase is apparent, as to breadth, in all three parts 

 of the sternum. On the other hand, while the total length of the bone is 

 greater over forty years, the increase (in both sexes) is seen to be due to 

 the greater length of the metasternum, and (in the male only) to the 

 greater length of the mesosternum. The male presternum and the female 

 mesosternum are actually shorter in the series over forty years of age than 

 in the younger bones. 



(J?) Sex Differences. 



While it is obvious (Table XI) that the male sternum is absolutely 

 larger, in both length and breadth, and in all three parts, than the female 

 sternum, there are several important differences in the relative size of the 

 parts of the bone, in the two sexes, as shown already by Hyrtl,** Strauch,*' 

 DwiGHT,'' and others. 



I . Presternum. 



Among the specimens in my collection, the average male presternum 

 measures in length 52*0 mm., and in breadth 65'3 mm. (Table XII). The 

 female presternum measures in length 47*3 mm., and in breadth 58"3 mm. 



