134 PROF. DR. L. BOLK 



fill, because, even in case of strong development the muscle 

 lacks a special function. But it is not permissible, I think, 

 upon these grounds to maintain the view that the sternalis 

 muscle is a symptom of degeneration. Its existence is simply 

 caused by a factor of an unknown, perhaps of a mechanical 

 nature, working upon the mass of embryonic tissue from which 

 the group of pectoral muscles differentiates. Beyond this the 

 real nature of this factor may remain open to question. 



Returning to our special subject, I wish to give a brief ac- 

 count of the variations of the human denture of today, which 

 seem to me to prepare for the construction of the future human 

 denture. From this point of view such variations may be dis- 

 tinguished as progressive ones, even though their essential char- 

 acter is that of morphological retrogression. 



The examination of the abundant material showing dental 

 anomalies present, in the Anatomical Museum of the University 

 of Amsterdam, has convinced me that the principal change 

 which will occur in the future will be the continuation of the 

 process which took place in the past and with which we became 

 acquainted in the first paragraph. 



The fundamental characteristic of the developmental history of 

 the human denture is the diminution in number of the constitu- 

 ent elements. This process is not limited to a single point of 

 our denture but proceeds at two points at least, viz.: in the 

 incisor region and in the molar region. I shall first consider the 

 reduction of our incisors. 



One of the most generally known indications of reduction in 

 our denture is that of the second incisor in the upper jaw. Often 

 this reduction is noted in several generations and members of 

 a family, so that in one family all degrees of reduction, and total 

 absence also, occur simultaneously. According to the investi- 

 gation of Rose, the anomaly occurs in about 2 per cent of the 

 German people. This author emphasized the fact that his in- 

 vestigations indicate no relation between the frequent absence 

 of this tooth or its reduction, and the shape of the facial skull. 

 In long-faced individuals the anomaly is as frequent as in broad- 

 faced ones. 



c 



