502 L. BOLK 



seat of a premature obliteration, and it is almost improbable 

 that this process is effected by an influence originating from the 

 middle-ear. Therefore it is necessary to explain the great fre- 

 quency of the closure of the masto-occipital suture in infantile 

 skulls in a quite different manner. We will return to this ques- 

 tion after having discussed the premature obliteration of the 

 sagittal suture, which resembles in many points the masto- 

 occipital. The number of all non-adult skulls, showing a closure 

 of the masto-occipital sutures amounts to about 10 per cent, 

 and we have found the same proportion in infants' skulls aged 

 3 to 6 years. The process is therefore limited to the period 

 before the commencement of the dentition and is not extended 

 over the whole period of growth of the individual. This fact 

 is proved by another statement given in table 2. It appears 

 that the number of partial coalescences diminishes when the 

 age of the skulls advances and that on the contrary the num- 

 ber of total coalescences increases with the age of the individuals. 

 To prove this let us compare the first two and the last two 

 groups with each other. In the first two groups are included 

 the skulls of children from 3 to 7 years. The total number of 

 these is 1125. In 28, or nearly 25 per cent, of these, a com- 

 plete coalescence of the masto-occipital suture was seen on 

 both sides. In the Groups VI and VII, including the skulls of 

 12 years and more to the adult state, there were 261 skulls, and 

 of these there were 12, or about 5 per cent, with complete closure 

 on both sides. The difference appears still more considerable 

 by comparing the unilateral coalescence. In the first two 

 groups there are 12 + 5 + 9 + 9= 35 completely closed sutures 

 on one side and 20 + 11 + 21 + 7 = 59 partially obliterated. 

 Therefore, in the very young skulls (Groups I and II) the cases 

 with partial obliteration greatly outnumber those with complete 

 obUteration. After the twelfth year (Groups VI and VII) the 

 correlation becomes reversed; total obliteration being then 

 more common than partial, proved by the following addi- 

 tion: totally closed 8 + 4 + 6 + 3= 21 and partially closed 

 3 + 1 + 5 + 3 = 12. 



