Anatomy. — "O71 the Significance of the Supra- orbital Ridges in 

 the Primates.'' By Prof. L. Bolk. 



(Gominuuicated at the meeting of F'ebruary 25, 1922). 



Tlie significance of any morpliological feature may be gathered 

 either from the function it performs, or from its mode of origin. 

 Of these two methods it is always best to follow the first and to 

 employ the second only when the first fails or yields unsatisfactory 

 results. That the first method yields more reliable results is sub- 

 stantiated by the fact that in the application of this method direct 

 observations are the basis for our conclusions, which in the other 

 case are supported at best by more or less plausible reasoning and 

 speculation about the possible influences and correlation of phenomena. 



What I wish to state about the significance of the supra-orbital 

 ridges in the Primates I have preceded by this contrast between the 

 two methods of scientific morphological research, since not long ago 

 the same subject was raised at one of our meetings by our fellow- 

 member Prof. Dubois, who chiefly adopted the second method. I also 

 propose to discuss the question of the supra-orbital ridges of the 

 Primates — about which I pronounced my opinion on a previous 

 occasion. However, in my discourse I will scrupulously keep within 

 the bounds of immediate observation. 



First of all let us consider the facts. When comparing the human 

 skull with that of Anthropoids — to which group I will confine 

 myself for the time being — we are struck at once by the difference 

 in conloui' where the cei-ebral crane passes into the facial skull. 

 That this difi'erence is accentuated by the orthognathy of the human 

 skull as contrasting with the marked prognathy of the Anthropoid 

 skull, is only of secondary importance for our problem. The Anthro- 

 poid skull has no external frontal vault, which is the reason why 

 some consider this skull to be flattened. This belief may be sup- 

 ported by the comparison of young Anthropoid skulls with those of 

 adults. In the former the supra orbital ridges are absent, which 

 makes the skull look much more like that of man. The ridges are 

 formed as the ape grows up. This development commences shortly 

 after the complete eruption of the milk set about the time when 

 the first permanent molar appears. 



