ON METOPISM 39 



has nothing to do either with brain development, or with the 

 higher or lower degree of intellectual evolution. 



Now I wish to express my opinion upon the aetiology of meto- 

 pism. In the introduction to this paper a brief account is given 

 of the phylogenetic history of the frontal suture, principally in 

 Primates. I summarize that among the Prosimiae in some fam- 

 ilies the frontal suture, as a rule, persists, while in others, on the 

 contrary, it disappears. In monkeys both frontal bones unite 

 together at a very early stage of development, but in some in- 

 dividuals the suture may persist. In Anthropoids till now the 

 suture has never been seen in an adult specimen. This summary 

 shows that in the course of the phylogenetic evolution of man, 

 originally both frontal bones remained separated; thereupon in 

 the higher degree of evolution the bones coalesced, and finally 

 in man the primitive state presents itself again in a number of 

 individuals. These facts form the basis for a conception of the 

 aetiology of metopism differing from those previously advanced. 

 For it seems to me necessary to begin by discovering the cause 

 which caused the suture to disappear in monkeys. Having elu- 

 cidated this point, we have approached more closely to the solu- 

 tion of the metopical "problem in man. For the possibility must 

 be taken into consideration that the influences which were acting 

 on lower Primates and caused the concrescence of the two fron- 

 tal bones, have lost their significance and activity in man. If 

 this really happened, it is quite comprehensible that the frontal 

 suture reappears. For in each individual both frontal bones 

 arise separately, the bilateral condition being the rule in the 

 younger stages of development even in such forms in which the 

 individual is born with an already single frontal bone. The 

 metopical suture in an adult individual hence represents no new 

 condition, no alteration of a primitive state, but simply the con- 

 tinuation of an original condition. There must be a special 

 cause for a union of the bones whereas there is no new fac- 

 tor required for the explanation of the fact that they may remain 

 separated. Let us therefore try to find out the primary cause 

 of the concrescence of the frontal bones in monkeys, afterwards 

 we can examine whether this cause became inactive in man or 

 not. 



