40 THE HUMAN STERNUM 



Out of five hundred and sixty-three sterna, young and adult, between 

 the age of two and eighty-two years, four hundred and sixty-seven, or 

 83 per cent., present what may be styled a normal presternal notch. The 

 notch in these cases varies considerably in width and depth. In one 

 hundred and ninety-three cases it is a well-marked wide concavity (PL VII, 

 Figs. 45, 46, 47) ; in one hundred and eighty-nine cases it is shallow 

 (Figs. 45, 46) ; and in eighty-five cases it is narrow (Fig. 47). 



In ninety-six cases (17 per cent.) there are deviations from the normal, 

 accompanied by the absence of a presternal notch. The variations that occur 

 are devisable into two main groups : (i) fifty-one cases (9*0 per cent.) in 

 which the upper border of the presternum is flat, convex, or raised into a 

 median projection ; and (2) forty-five cases (7*9 per cent.) in which two 

 lateral projections or separate ossicles occur. 



In the first series sixteen examples occur in which the upper border 

 of the presternum is a horizontal, straight, or irregular line. In twenty- 

 three cases it is convex ; in twelve cases it is raised up into a distinct median 

 projection (PI. VII, Figs. 48, 49). 



In the second series the projections from the presternum are bilaterally 

 placed. In one case only (o'i7 per cent.) are there two separate supra- 

 sternal ossicles (Fig. 50). In another case there is a prominent tubercle on 

 the left side fused with the presternum, and on the right side a sessile 

 tubercle surmounted by an articular facet* (PI. VII, Fig. 51). 



The remaining cases, forty-three in number, are examples of the 

 presence of lateral tubercles on the upper border of the presternum, which 

 fall into four groups not clearly separated from each other, (i) There are 

 eleven examples of prominent tubercles bilaterally placed upon the upper 

 border of the presternum (PL VII, Figs. 52, 53) ; (2) there are ten cases in 

 which the projections form ridges separated by grooves or notches from the 

 clavicular facets (Fig. 52). Again, there are twenty-two cases in which 

 there are distinct articular projections (Fig. 54) (3) separate from or (4) 

 continuous with the clavicular articular surfaces. 



Of the last-named series, probably not all are undoubted suprasternal 

 ossifications. Some (in group 3) appear to be facets for the articulation of 



* More recently I have obtained a third example (PI. VII, Fig. 44) not included in the scries, with an 

 articulating separate ossicle on the left side, and an articular facet upon the right side. 



