4 THE HUMAN STERNUM 



Professor Cleland's position as one of the most independent and 

 philosophical anatomists of the present day, entitles any view which he 

 expresses to weighty consideration. ' The sternum,' he says, ' there can be 

 no doubt, is at first laid down in the form of two lateral slips at right angles 

 to the tips of the costal cartilages. It is impossible, however, to refer these 

 slips to prolongations from the costal tips. Judging from the appearance 

 in the third month, the manubrium may be originally continuous with 

 the first pair of costal cartilages, but the mesosternum takes its origin distinct 

 from costal cartilages, and the xiphisternum is at first separated from the 

 mesosternum by the sixth and seventh costal cartilages meeting in the 

 middle line. 



' The origination of the sternum in lateral parts explains the well- 

 known case of M. Groux, in whom the two halves remained ununited, 

 and could be pulled separate by the great pectoral muscles when the hands 

 were clasped. Less complete division also occurs. The original distinct- 

 ness of the lower parts of the sternum from the costal arches may be well 

 kept in mind when comparing it with the chelonian plastron.' * 



This is the main idea that I have to bring forward. The studies into 

 which one has been led in this investigation have, however, brought to the 

 front several minor questions of some importance to which one may be 

 allowed to draw attention in due course. 



FissuRA Sterni 



One aspect of the subject has not been personally studied — teratology 

 of the sternum ; so that it may be contended that thereby one of the 

 strongest arguments (namely, the existence of a sternal fissure) in favour of 

 the bilateral and costal origin of the sternum is evaded. Now the occurrence 

 of fissura sterni has been one's greatest difficulty in an a priori acceptance of 

 the orthodox view of the origin of the bone. From a study of the literature 

 of the subject and from searches in museums, one finds it an extreme rarity. 

 The museum of the Royal College of Surgeons does not possess a specimen. 

 If the sternum is costal in origin this ought surely not to be so. All the 

 factors engaged are tending, during the process of growth and ossification, 



• Cleland and Mackay, Text-Book of Anatomy, pp. 130-131. 



