20 THE HUMAN STERNUM 



The mesosternum and metasternum are usually (77*9 per cent.) united 

 by cartilage, and only exceptionally (22-1 per cent.) by a fibrous lamina. 



The costal cartilages in the centre of the series are generally fused with 

 the lateral borders of the sternum, and are not united to it by a fibrous 

 lamina. The first costal cartilage is also, as a rule (81-3 per cent.), con- 

 tinuous with the presternum. Occasionally on one side or both the union 

 is fibrous. 



The condition of the seventh and eighth costal cartilages has been 

 particularly noted. It is not uncommon for the seventh pair of cartilages to 

 articulate together in front of the sternum (thirty-four cases — 14-4 per cent.) 

 (In still fewer cases the same occurs with the sixth costal cartilage). In 

 8 per cent, of the cases the seventh cartilage fails to reach the sternum on 

 one side or both. On the other hand, the eighth cartilage on one side or 

 both is connected with the sternum in still fewer cases (4*8 per cent.) In 

 rare cases, the fifth, sixth, or seventh cartilage reaches on one side to the 

 middle line of the sternum, its distal end pushing its way forwards through 

 the body of the sternum. 



Shape of the Metasternum. 



Out of one hundred and eighty-nine cases, the metasternum is present 

 in one hundred and eighty-two (96*3 per cent.) ; absent in seven instances 

 (3*7 per cent.) I have been as careful as possible to discard all examples in 

 which there was the slightest indication that the metasternum had been 

 accidentally lost in maceration. 



While the shape is extremely variable, it is more often pointed and 

 median than bifurcated. An undivided metasternum occurs in one hundred 

 and seven cases (57'6 per cent.) ; a bifid metasternum in seventy-seven cases 

 (42-3 per cent.) 



ylnomalies in Development. 



One of the most striking features of the series of embryonic sterna 

 examined is the absence of anomalous conditions, and the regularity and 

 symmetry of development. No case of fissura stemi is recorded. One 

 example occurs of transference of the pre-mesosternal junction to the level 



