THE LEMURS. II 
There is an oblique ridge between the hind outer and the 
front inner cusp, and another is often present between the 
front outer cusp and the anterior “‘heel,” producing, as Huxley 
has pointed out, almost a double crescentic pattern, as in many 
lower Mammals. The posterior molar has four or five cusps. 
Of the m/k-teeth, the incisors in the upper jaw change first. 
Of the molars, two are developed before the change of the 
pre-molars. In the lower jaw the incisors change first, and 
when two or three pre-molars have developed the last molar 
has still to come. 
The arm-bone, or Aumerus, has one perforation (entepicondylar 
foramen) on its inner margin, and another above the joint 
(except in Lerodicticus). The bones of the fore-arm (vadius 
and wdna), and those of the leg (dia and fibula) are not 
co-ossified (except in Zarsiis),so that the palm or sole can be 
turned up at will. 
The bones of the dzg?#s are more or less flat and rounded 
at the tips (differing in this respect from the Zysectivora). One 
of the ankle-bones, for the articulation of the opposable great 
toe, the ento-cuneiform, as it is called, is rounded, as in the 
Anthropoid Apes and Man. The thumb is opposable, but its 
articulating bone in the wrist is not rounded, except in Avahis 
and /nzdris, which genera agree in this respect with Axthro- 
popithecus and Man. The wrist has its central bone (os centra/e) 
present ; it is absent in Man and the higher Apes. 
The knee is free and not united to the side of the body by 
integument. 
The two halves of the lower jaw are not always co-ossified (as 
is the case in the Anthropordea). 
The opening in the base of the skull (the foramen rotundum) 
which transmits from the brain a branch of the fifth nerve 
