THE HUMAN STERNUM 



25 



elements of the mesosiernum. The series may be subdivided at the nine- 

 teenth year. Stci-na ol nineteen years ami over usually possess mesosterna, 

 in which the el^'uicnts are fused fojictiier. In sterna of eighteen years or 

 less tlie coniiioncnt elcnunts of the mcsosternum are usually separate. 

 Alicr the ,1'j^e of iorty-onc (in two hundred and ninety-nine sterna between 

 fortv-two anil e!'j;hty-two years, inclusive) the mesosternum is always a single 

 midividcd mass. 



Out of f)ne luinJrcd and sixty-one sterna between twenty-six and forty-one years, 

 inclusive, the mesosternum Is .i single bone in one hundred and fifty-five cases {()6'Z per cent.) 

 'I'hc six exceptional mesosterna consist in ever)' case of two pieces, separated in five examples 

 between the first and second elements, and in one between the third and fourth. 



|. I 2 + 3 -b (?) + 



Among forty-four sterna between the ages of twenty and twenty-five years, the meso- 

 sternum is a single piece in thirty-six cases (S 1 '8 per cent.) There are nine exceptional cases, 

 in eight of which the mesosternum is in two pieces ; in one it is in three pieces. 



aei. 



(9) M 



21 

 23 

 ^4 

 25 



20 

 21 

 20 

 20 



\-i 2 -f- 3 -h (?) 4 



1 -b 2 -b 3 -4 



■1+2 3 + 4 



I I 3+4 



In five cases the cleavage is between the first and second elements ; in two cases between the 

 third and fourth ; in one between the second and third ; and in one instance the second 

 piece is separate from both first and third. 



Among seventeen sterna at nineteen years, the mesosternum is a single bone in ten 

 cases (58S per cent.) Of the remaining seven cases, in five the first piece is separate ; in 

 one the first and second pieces are separate ; and in one case all the elements are separate. 



Below the age of nineteen, as already stated, the mesosterna! elements are more frequently 

 separate than fused. 



