THE HUMAN STERNUM 



33 



of the sterna of embryos and children after birth — taken together — it is not 

 quite easy to harmonize them with those presented in my own personal 

 observations. This is a matter for regret, as it appears that we have been 

 simultaneously working along similar lines. Our results do not agree 

 statistically, but as will be shown later there are certain broad generalisations 

 which can be stated from a comparison of the two series of observations. 



Dates of Ossification of parts of the Sternum 



Presternum. 



Whereas my observations show that a centre (or centres) for the 

 ossification of the presternum usually occurs in the sixth month, Markowski 

 states that it begins to appear at the fourth or fifth month. In regard to 

 the number of centres, a general agreement exists between us. A single 

 centre is most common {M.., 68-4 per cent. ; P., 79 per cent.) ; double 

 centres are less common (M., 29 per cent, (vertical) ; P., 17*2 per cent, 

 vertical, i per cent, horizontal) ; three centres (or more), 2*6 per cent, in 

 both cases. He does not make any observations on the union of the pre- 

 sternum and mesosternum ; and regards the presternum as morphologically 

 associated with the first and second ribs. 



Mesosternum. 



There is general agreement in the two series of observations, in regard 

 to the main facts observed, although statistically wide differences are apparent. 

 The comparison between the two series of observations of the ossification of 

 the mesosternum may be readily shown in a tabular form : — 



Mesosternum Date of Appearance 



Date of Union I | M. P. 



P. i M. 



16 — 20 years] 13th year 



21 — 25 years { 

 complete 



7 — 1 1 years 50% 



II — 15 years J 



o — 15 years 



5 th month 

 5 th month 



6th month (66-6%) 

 7th month (77-4%) 



7th & 8th month 7th month (54'8X) 



59% before birth") 



1 5% after death > 8th month {'ij'^y^ 



26% absent 3 



9th month {once) never 



