637 



squamosa, so that tlie region of tlie frontal process is included in 

 the alisphenoïd. 



Sometimes tlie spheno-parietal suture lies at the level of the lower 

 border of the frontal process; so that the region of this process is 

 included in the parietal. The region of the frontal process of one 

 side can be included in the frontal, as is proved by a skull, which 

 presents at the left side a frontal process of the temporal and at 

 the right side a symmetrical temporal process of the frontal. 



If at the side opposite to the frontal process one or more ossa 

 epipterica are found, the situation and extension of these bones are 

 equal to those of the frontal process. 



We find other relations in the skulls with frontal processus of the 

 second type. Here the enlargernent of the squamosal is nearly always 

 absolutely symmetrical. 



Only once did I find a second type of frontal process at one side 

 and an os epiptericum typicum at the other one. 



I suppose that the question after genesis and significance of the 

 above mentioned two types of frontal processus must be answered 

 as follows. 



The proc. frontalis of the first type is to be considered as the 

 homologon of an os epiptericum typicum. Following arguments led 

 me to this opinion. 



In the first place it is possible that the region of a unilateral 

 proc. frontalis can be included at the opposite side in one of the 

 surrounding bones (sphenoid, frontal, parietal). 



In the second place it must be remembered that the ossa epipterica, 

 which are present at the side opposite to the frontal process, corre- 

 spond in their extension and situation to this process. 



When we find a frontal process together with an os epipte- 

 ricum at the opposite side, these two correspond with the frontal 

 process. 



At last I have to mentioji the great variability in form and 

 extension of the proc. frontalis. As 1 will explain further on, we 

 can find that in a skull with a unilateral os epiptericum or ossa 

 epipterica the opposite side sliows the same conditions as in a skull 

 with a unilateral processns frontalis of the first type. 



The frontal process of the second type, the enlargement of the 

 whole squamosal, could be due to two causes. In the first place we 

 can suppose that merely an enlargement of the squamosal is cause 

 of the exclusion of the alisphenoid from the frontal, in the second 

 place we can imagine that this enlargement is due to the opposition 

 to the squamosal of that part of the alisphenoid which is not 



4i 

 Proceedings Koyal Acad. Amsterdam. Vol. XVI. 



