14 THE HUMAN STERNUM 



compel us to hesitate before accepting the conclusions arrived at by the 

 author as final. 



It is extremely difficult to summarize and classify the views of authors 

 regarding the development and morphology of the sternum. Rathke," 

 who first described its development in the chick, gives nowhere any sugges- 

 tion that the sternum is not originally separate from the ribs. Bruch 

 later describes it as formed independently, and secondarily connected with 

 the ribs. Ruge," Hoffmann/' and others have maintained the opposite 

 view, that the sternum is wholly derived from costal elements, while 

 GoETTE^' inclines to a middle view, which appears to me to contain a certain 

 fallacy and at the same time to possess a certain basis in fact. He holds 

 that the presternum is partly derived from the shoulder-girdle (clavicle), 

 partly from the ribs, that the mesosternum is wholly costal, and that the 

 metasternum is a derivative of the mesosternum. 



On account of the fact that Ruge's memoir has been the mainstay 

 of the exponents of the theory of the costal origin of the sternum, one 

 has had to examine it with the greatest care. It is an admirable piece of 

 investigation. But, writing with all deference, I venture to submit that, 

 granting the accuracy of all the observations made, exactly the opposite 

 conclusion may be drawn from the memoir ; and it is further open to 

 observe that most of the writers who have followed Ruge have been more 

 dogmatic than he is in their statements of Ruge's observations. 



Ruge's evidence in this matter is of such importance, and his observa- 

 tions of such material assistance in the elucidation of this problem, that it 

 is desirable to review a few of his statements. 



The points brought out by a careful examination of his memoir may 

 be stated in the following propositions : — 



1. The sternum in the earliest stages examined by Ruge consists of 

 two longitudinal strips {sternal leiste), which may be traced into the 

 abdominal wall, and there fade away into indifferent tissue without a distinct 

 line of demarcation. But no statement is made of the character of the tissue 

 that occurs in the middle line between the two strips. 



2. These sternal strips are joined by the distal ends of the ribs. 

 But the earliest stage shown is one in which, while the three proximal ribs 



