34 L. BOLK 



a heightened intracranial pressure during growth due to a greater 

 development of the brain, is considered to be the cause of metop- 

 ism. Now, I cannot agree with this opinion, for as clearly shown 

 in the foregoing pages, metopism is independent of the shape 

 as well as of the size of the skull. And if there really existed 

 some relation between the degree of development of the brain 

 and the frequency of metopism, one should expect among the 

 largest skulls an increased number of metopical specimens and 

 higher average values of the mean dimensions in metopical 

 skulls. This is not at all the case. The averages of the three 

 dimensions in metopical skulls are nearly the same as in the non- 

 metopical. Therefore a noticeable difference between the ca- 

 pacity of both groups of skulls cannot be accepted, and con- 

 sequently the average weight of the brain must be the same. 



An objection of more general theoretical nature against the 

 current opinion about the etiology of metopism may be adduced. 

 Is it really true that an increase of the intracranial pressure may 

 prevent the coalescence of two bones of the skulls whose normal 

 fate is to unite together? Martin, the renowned anthropolo- 

 gist, accepts this view, founding his opinion upon hydrocephalic 

 skulls, in which, as he says, metopism is a common phenomenon. 



I do not know how far this statement of the painstaking in- 

 vestigator is based upon observations by himself, or is merely 

 the expression of a doctrine propagated in craniological lit- 

 erature. I am inclined to believe the latter. For the experi- 

 ence gained by myself upon this matter is in contradiction with 

 the idea mentioned. There is no concurrence of hydrocephaly 

 and metopism, hydrocephaly being not at all a condition pro- 

 pitious for the persistance of the frontal suture. I have examined 

 carefully the hydrocephalic skulls present in the anatomical 

 Museum of Amsterdam, and the results of this investigation are 

 dealt with in the next table. This table informs us of the state 

 of the frontal suture the horizontal circumference of the skull 

 and the age. With regard to the circumference it may be 

 remarked, that in normal Dutch skulls it amounts to 516 mm. 



