THE EVOLUTION OF THE EYEBROW REGION OF THE FOREHEAD. 295 



Semnopithecus and Cercocebus the fusion of the three elements of the supraorbital region 

 was very nearly complete, but in the region of the trigonum the superciliary element 

 showed as a distinct ridge above the outer part of the orbital margin. In these cases 

 the supraorbital notch fails as a guide to the line of separation between the superciliary 

 and other parts of the region. 



Schwalbe gives a careful and accurate account of the supraorbital region in the 

 cranium of Pithecanthropus erectus, in so far as this can be studied in the plaster cast 

 of the specimen, and he supplements his remarks by a drawing. I have had the 

 advantage of being able to examine two casts of this cranium, one of which was 

 presented to me by Dr Eugene Dubois when he visited Dublin, and another which he 

 gave to Sir William Turner. Both of these specimens are in the Anatomical Museum 

 of the University of Edinburgh. They are sharp and excellent casts, and they agree 

 in every particular with Schwalbe's description. I am thus able to confirm Schwalbe's 

 view that the eyebrow region presents the form which I have included under Type II. 

 It should be noted, however, that the fusion between the superciliary and the supraorbital 

 elements is very nearly complete, and the condition is one which closely corresponds to 

 that which is frequently seen in the aged Anubis baboon. Indeed, from the appearance of 

 the eyebrow region I think we may conclude with some degree of certainty that the 

 cranium of Pithecanthropus erectus is that of an aged individual. 



As Schwalbe points out, it is an important and significant fact that it is to the 

 baboon, much more than to the gorilla or chimpanzee, that Pithecanthropus erectus 

 shows a resemblance in this respect (6). 



Type III. — In this form of the supraorbital region all the three elements which 

 enter into its formation become fused together so as to constitute a continuous arch, 

 the torus supraorbitalis, which bounds the orbital opening above and forms a varying 

 amount of the fore-part of the roof of the orbital cavity. This arch extends from the 

 glabella to the fronto-malar suture, and in its typical condition it shows no trace of the 

 constituent elements of which it is composed, so completely have these become blended 

 the one with the other. Of such a nature is the supraorbital region in the adult 

 chimpanzee, in the gorilla, and in a large number, if not the majority, of the lower apes 

 of the Old World. Still, it is not correct to suppose that even in the gorilla and the 

 chimpanzee this is the only condition of the eyebrow region which may be present, and 

 that there never occurs an approach to the form distinctive of Type II. In young 

 specimens of the chimpanzee the superciliary eminence, although fused with the 

 supraorbital torus and not marked off on its outer side by any distinct groove, is yet as 

 a rule easily discernible, not only by the greater degree of prominence of this part of 

 the arch, but also by a difference in its texture. The same also may be occasionally 

 seen in the adult chimpanzee. In such cases the supraorbital notch, which Schwalbe 

 takes as the demarcation between the supraorbital and superciliary elements, fails to be 

 a true guide. The superciliary element extends outwards in the torus far beyond this 

 point. In the beautiful illustrations of anthropoid crania which are given by Selenka, 



