12 
MUSEUM BULLETIN NO. 9. 
method of mastication, and carried out with the powerful biting 
muscles in a high state of contraction. (2) The fact that the 
whole process is begun at a very early age. This second con- 
sideration is of great importance, as it is in the young growing 
skull that environmental reactions produce a lasting effect. 
Finally, the pressure of the condyle on the eminentia articularis 
has resulted in the prevention of the downward development 
of the latter, and has rolled and flattened it out in the manner 
presented to us so frequently in their skulls. 
In the anthropoid ape the glenoid fossa is shallow and the 
eminentia articularis flattened (see figures 9 and 10, Plate II), 
but this cannot be put down to a side-to-side movement in masti- 
cation, as Dr. Keith has pointed out its impossibility in their 
case; it may possibly be due to the very heavy mandible and, 
proportionately to the size of the cranium, huge condyles, 
combined with extensive forward movements of the condyles 
in opening and closing the mouth and an antero-posterior 
movement of the same in mastication. 
To sum up, then, in any primitive race where the food is 
tough, cookery imperfect, and strenuous side-to-side mastication 
needed, we should, I think, expect to find examples of shallow 
glenoid fossae, but in none of them would this be so marked or 
so universal as in a race such as the Eskimo, living almost 
exclusively upon a diet of tough and poorly cooked flesh. 
In modern highly civilized man, on the other hand, 
where, owing to the soft well-cooked nature of the food, 
such strenuous masticatory movements are no longer necessary, 
a scissor-like snapping action of the teeth being substituted 
for the vigorous side- to side grind of primitive man, the condyles 
in the action of trituration need never move far or with great 
force out of the glenoid fossae; while, owing to the small extent 
to which the jaws diverge in the act of mastication, and to the 
absence of any necessity for powerful biting movements, the 
condyles of the mandible during mastication need never press 
with that hard rolling action upon the eminentia articularis. 
Hence in these races we find a deep glenoid fossa and a high and 
prominent eminentia articularis. 
