250 COPE. (VoL. 1H. 
necessary in many of the bunodonts by the structure of the 
glenoid cavity of the squamosal bone, which grasps the condyle 
of the lower jaw in front and behind, forbidding any but a direct 
movement. This is the case in the peccary, but it is not found 
in the hippopotamus, the Quadrumana, or the Anthropoidea. 
In the lophodonts, type one (mostly Ungulata), the mandibular 
condyle is not confined in front, and thus it has free lateral 
movement. In the second type of lophodonts (Rodentia and 
Proboscidia) the condyle is not confined anteriorly or poste- 
Figure 74. — Skull articulations of the mandible in a, 4, c, the giraffe; d, e, wild 
cat; and f, 9, Hydrocheerus. Figs. @ and f, vertical views; 4, e, and g, profiles; and 
c and d, posterior views; from Ryder. 
riorly, but is bounded by a lateral longitudinal crest of the 
squamosal bone. The movement must be, therefore, fore and 
aft, whether the mouth be much opened or not. 
We may now examine the cause of the evolution of the lopho- 
dont, type one, from the simple bunodont. Both types exist 
within the order Diplarthra, and it has been already shown that 
the former have descended from the latter in each suborder of 
that order. 
In the accompanying figure (75) from Ryder the movements 
of the lower jaw in mastication of lophodonts, are diagramma- 
tically represented. Fig. @ represents the movement in Car- 
nivora, and in the orthal bunodonts, as the pigs. Fig. 6 shows 
a slight lateral movement believed by Ryder to exist in the 
wart hog (Phacochcerus). Fig. ¢c represents the movement in 
