302 



PROFESSOR D. J. CUNNINGHAM ON 



sulcus supraciliaris. As the brain advances in its phylogenetic growth, it reduces the 

 width of this sulcus, encroaches upon the eyebrow projection, and extends the area of 

 the orbital plate of the frontal bone which intervenes between the cerebrum and the 

 orbital cavity. 



At the same time it should be noted that even in the European a considerable part 

 of the orbital roof may be formed by the supraorbital projection of the frontal bone. Id 

 fig. 7 is shown a sagittal section through the head of an Irish subject in which the eye- 

 brow region was somewhat prominent. It will be seen that very nearly one-third of the 

 orbital roof is formed by the under surface of this part of the frontal bone. Further, it 

 will be noted that three-fourths of the eyeball lie in front of the brain and under shelter 

 of this portion of the bone. 



cerebral part of the 

 roof of the orbit. 

 ,- Arcuate eminence 

 on face. 



Pre-cerebral part of 

 roof of the orbit. 



Fig. 8.— Sagittal section through the frozen head of a 

 young male chimpanzee, in a plane to the outer 

 side of the mid-point of the supraorbital arch. 



Ficj. 9. — Sagittal section through the frozen head of an 

 adult gibbon {Eylohatcs agilis) in a plane corre- 

 sponding to the mid-point of the supraorbital 

 arch. Note the large share which the torus supra - 

 orbitalis takes in the formation of the roof of the 

 orbit. 



Those familiar with the facial aspect of the gorilla and chimpanzee know that the 

 torus supraorbitalis is not only concerned in forming a large part of the wall of the 

 orbit, but also in producing a strong arch-like projection which juts forward on the face 

 above and in front of the eyeball. Fig. 8 was obtained from a tracing of a sagittal 

 section of a young chimpanzee (probably about three or four years old) ; the torus 

 is thus far from having attained its full degree of development. Still, the manner in 

 which it forms the facial feature referred to is manifest. In one respect this 

 section cannot be compared with the other sections shown in figs. 7 and 9. The 

 impression which it gives of the relation presented by the roof of the orbit and the 

 brain to the eyeball is somewhat misleading. It will be noticed that the section 

 has been made through a different plane. Had it passed through the same plane 

 as in the case of the human head, the relation presented by the eyeball to the roof 

 of the orbit and the brain would not have been markedly different from what we 



