4 ALLEN’S NATURALIST’S LIBRARY. 
mouth are the two maxillze, along the margins of which are placed 
the grinding- or cheek-teeth ; the two pre-maxillz, in which are 
set the cutting- and the eye-teeth ; and lastly, the palatine bones 
which form the roof of the mouth. Hinged on to the,sides of 
the cranium is the toothed mandible, or lower jaw, composed 
of two halves, which may be solidly or loosely joined together 
in the mid-line, or symphysis. Along the under surface of 
the skull, there are, besides the great (often posterior) orifice 
for the entrance of the spinal cord, numerous foramina, 
or openings, for the passage of blood-vessels for the nourish- 
ment of the brain, and of nerves which bring all parts of the 
body into relation with the supreme directing centre. Con- 
spicuous near its posterior part, on each side, is an ivory-like 
capsule, the periotic bone, containing the essential organ of hear- 
ing. Lying beneath the lower jaw is the hyoid arch, a slender 
framework of bones, supporting the tongue and the upper end of 
the windpipe with the organ of voice. Ina few of the Monkeys 
and Apes certain of the bones of this arch are much enlarged 
and hollowed for increasing the volume of sound emitted by 
them. On either side of the great opening which is so conspicu- 
ous at the hinder part of the skull, for the reception of the spinal 
cord, is a smooth kidney-shaped surface, called a ‘ condyle.” 
These two condyles serve for the articulation of the first 
segment of the back-bone to the cranium, and by the posses- 
sion of this pair of condyles the Mammalian skull can always be 
distinguished from that of Birds and Reptiles. ‘The pieces of 
which the back-bone are composed are named the verlebre. 
Those of the neck, the “cervical” vertebra, are recognised by 
having no true ribs attached to them, and are, in all Primates, 
seven in number. ‘Those of the back, or “ dorsal” vertebrae, 
may be distinguished by having articulated to them, on cach side, 
