THE STEKNUM : ITS EARLY DEVELOPMENT AND OSSIFICATION. 31 



While the shape is extremely variable, it is more often single 

 and median than bifurcated. An undivided meta-sternuni 

 occurs in 107 cases (57"6 per cent.) ; a bifid raeta-sternum in 

 77 cases (42-3 per cent.). 



(F) Anomalies — L'pi-sternal cartilages. — One of the most strik- 

 ing features of the series of embryonic sterna examined is the 

 absence of anomalous conditions, and the regularity and sym- 

 metry of development. No case of fissura sterni is recorded. 

 One example occurs of transference of the pre-meso-sternal 

 junction to the level of the third costal cartilages. A few 

 instances are found in which one or more costal cartilages 

 (usually the 5th, 6th, or 7th) force their way through the 

 cartilaginous sternum to the middle li6e. Absence of the 

 meta-sternum, asymmetry in the attachment of costal carti- 

 lages, and fusion of contiguous costal cartilages together, also 

 occurred in a few examples. 



Ein-sternal cartilages. — In two cases supra-sternal cartilages 

 have been found, situated at the cephalic border of the pre- 

 sternum, between the clavicular articular surfaces. In one case 

 the cartilages are separated from the pre-sternum and fused 

 together ; in the other case, they are separate from one another, 

 but continuous with the cartilaginous pre-sternum. 



It is not my desire to make any general deductions, or attempt 

 to draw any definite conclusions from these observations at 

 present. The subject is a large one, and is only very partially 

 dealt with in this communication. I have ventured to make 

 this bare statement of fact to the Anatomical Society, partly in 

 order to clear the way for further work on the same subject, and 

 partly to draw attention to some of the general morphological 

 problems associated with a study of the human and mammalian 

 sternum. 



[Description 



