THE EVOLUTION OF THE EYEBROW REGION OF THE FOREHEAD. 



301 



element, and in which the supraorbital region presents a close resemblance to the 

 condition present in the orang. In most cases, however, there is a strong tendency 

 exhibited for the inner end of the supraorbital arch to swell out into a bulbous ex- 

 tremity at the glabella. This in all probability is the superciliary element ; indeed, it 

 may sometimes be seen to partially disengage itself from the supraorbital arch and 

 present a condition which may be classed under Type II. 



Relation of the Supraorbital Region to the Orbit. 

 Schwalbe rightly lays stress upon the fact that in the majority of apes the supra- 



Pre-cerebral part of the 

 roof ol the orbit. 



Fig. 7. — Tracing from a sagittal section through a frozen male head (Irish), in a 

 plane corresponding to the mid-point of the supraorbital arch (reduced). 



orbital eminence, which juts forward in a shelf-like manner from the front of the true 

 brain-capsule, forms a considerable part of the roof of the orbit. The degree of promi- 

 nence to which this condition may attain varies in different groups, and may be 

 demonstrated by making a sagittal section through the frozen head in a plane which 

 passes through the mid-point of the supraorbital arch. This method has the further 

 advantage of showing the relation which this pre-cerebral part of the roof of the 

 orbit presents to the eyeball. 



In the adult male gorilla the torus supraorbitalis may form as much as the anterior 

 half of the orbital roof, and a similar relationship may also be seen in a pronounced 

 form in the chimpanzee, baboon, and other forms of ape. This character is strictly 

 correlated with the extent of the area to which we have applied Schwalbe's term of 



