496 L. BOLK 



has closed itself and the different parts of the occipital bone are 

 united with each other. The sutures still existing at this date 

 of life, are the so-called persisting sutures remaining for a shorter 

 or longer time after the individual has become full grown. Re- 

 garding the variability of age in which these sutures disappear 

 there are already some extensive and carefully written com- 

 munications, for instance by Fredericg and Nibbe. Yet it is a 

 well-known fact that now and then one of these persisting sutures 

 does close during childhood before the individual has reached 

 the adult state. Of this fact, and its influence on the shape of 

 the skull, the casuistic literature is already very abundant, 

 but a systematical inquiry into this phenomenon is as yet 

 wanting. In the present paper I wish to deal with the results 

 of my examination of the premature concrescences of bones in 

 the human skull, results acquired by the investigation of 1820 

 skulls of non-adult individuals. I regarded the obliteration of 

 the occipito-sphenoidal synchondrosis as a criterion of the 

 adult condition of the skull. The youngest skulls at my disposal 

 already possessed their complete milk-dentition, therefore in this 

 communication skulls of the first two years are not mentioned. 



Before beginning my investigation I divided my collection 

 into seven groups, in accordance with the developmental phase 

 of the dentition. Of the different groups a brief description 

 follows : 



Group I. This first group is composed of the very young 

 skulls, with complete milk dentition, and therefore with the 

 following dental formula: 



i. i. c. in. 111. 



These skulls, 725 in number, are those of children who died 

 between the third and sixth year. 



Group II. This group includes the skulls in which, besides 

 the complete milk dentition, the first permanent molar tooth 

 is also present. The dental formula of these skulls (of children 

 aged 6-7 years) is as follows: 



i. i. c. m. m. M. 



This second set comprises exactly 400 skulls. 



