48 THE HUMAN STERNUM 



which two other asymmetrical features are associated (probably compen- 

 satory in character) — obliquity of junction of the presternum and meso- 

 sternum, and a higher level of the left sterno-clavicular articulation. 



The development, ossification, and form of the human sternum 

 taken together present a picture of which the essential feature is median 

 position. If the human sternum were bilateral in origin, more frequent 

 examples might be expected of cleavage of its lateral parts. Sternal 

 foramina are not indications of fissure ; the presternum is always median 

 and imperforate ; the mesosternum in its cartilaginous form is median, 

 and its ossification is more often median than bilateral. The metasternum 

 is always median and ossified by a single median centre ; and is more 

 often pointed or rounded than bifid at its extremity. 



The connexion of the sternum with the costal cartilages is variable, 

 but without producing variations in its own intrinsic form ; the develop- 

 ment and ossification of the bone give no indication of any essential 

 metameric dependence upon the association with rib elements, except what 

 may be due to mechanical influences. 



Neither the cartilaginous sternum nor the centres of ossification agree 

 or vary with the number of associated ribs. 



