22 THE HUMAN STERNUM 



it so as to form spurs or sternal cornua, which provide a more extensive 

 surface for the articulation of the sternal end of the clavicle. These sternal 

 horns are present in 71 per cent, of the sterna in my possession over the age 

 of twenty-five years. Among those between twenty-five and thirty years 

 there are twenty-five examples out of fifty-six sterna. Of sterna under 

 twenty-five years, only three possess these projections — two at twenty-one, 

 and one at nineteen years. 



These sternal horns increase the width of the adult bone, and must 

 be taken into account in the transverse measurements of young and adult 

 bones, respectively. 



There is no doubt that in some cases at least the first costal cartilage 

 has a share in forming the articular surface for the sterno-clavicular joint — 

 Testut,'^' Morris,"** Anthony' — and these sternal horns are produced by 

 ossification, which serves the purpose of extending the area of the sterno- 

 costal articular surface. 



The presternum is complete at sixteen, and is supplemented between 

 twenty-five and thirty years by the addition of these cornua. 



Albrecht' (quoted by Anthony') contends that theoretically the 

 human presternum contains sixteen centres of ossification — two ' hemi- 

 sternebrae' in front of the first pair of thoracic ribs, two between the first 

 and second pairs ; two 'hemi-post-omosternums' (the omosternum of the 

 batrachia) ; two ' pre-para-sternals ' representing the sternal ends of the last 

 pair of cervical ribs ; two para-sternals representing the sternal ends of the 

 first thoracic pair ; two subclavicular epiphyseal points ; two caudal hemi- 

 epiphyses belonging to the second pair of hemi-sternebrae ; and two hemi- 

 epiphyses corresponding to the Lophosteon of birds. 



Rambaud and Renaut'* describe a case of the occurrence of five 

 centres of ossification in the presternum of a full-time foetus. In Quain's 

 Anatomy''' a presternum is figured with six centres. Anthony' found at most 

 three centres in his cases, and more often two ; one superimposed above the 

 other. He agrees with the facts adduced by my observations, and by others 

 (Rambaud and Renaut, Testut,*' and Markowski"^) that the presternum 

 is usually ossified from one centre and more rarely from two. 



