MAMMAL GALLERIES. 
skull and teeth ; the latter of which, although really no part of 
the internal skeleton, have, from their intimate relation with the 
skull, to lie treated as though they belonged to that element. 
.The skull consists of three parts — (1) the brain-case, or 
cranium^ a complicated framework of bones united to form a case 
for the brain, and a support and protection to the organs of smell, 
sight, hearing, and taste ; (2) the lower jaw, or mandible ; and 
(3) the hyoid arch, or tongue-bones. 
The brain-case forms in its posterior half a large hollow 
chamber for the brain, and has in its base numerous perforations, 
or foramina, for the passage of nerves and blood-vessels. In 
front of this case, and separated by a sieve-like bone, the cribri- 
form 'plate (fig. 2, ce), is a bony tube, open in front at the nostrils, 
or anterior nares {an), filled with light spongy bones, the turbinal 
bones (t), and forming the nose-chamber. Below this chamber, 
and forming in part its floor and walls, is the upper jaw, 
composed of the maxillary and premaxillary bones fmx and 
jomx), in which are implanted the upper teeth, the lower ones 
being similarly fixed along the upper edge of the lower jaw. In 
an upper view of the skull the component parts of its roof are 
seen as paired bones placed one in front of the other along the 
middle line. Of these the hindmost are the parietals {pa), pre- 
ceded by the frontals ( fr) and by the small and narrow iiasal 
bones (yia), placed between the upper edges of the maxillary bones,, 
where these rise to form the side-walls of the nasal chamber. 
External to these bones are the cheek, or zygomatic, arches 
(fig. 1, zy), which serve to support and protect the biting- 
muscles, and are more or less developed in direct proportion to 
the biting-power of their owners. The hindmost part of the skull 
is made up of the siipraocchpital (fig. 2, so), a pair of exoccipitals 
{exo), and the basioccipitcd (bo), surrounding the large opening- 
— the foramen magnum — through which passes the spinal cord. 
The lower jaw consists simply of a pair of solid bones, joined 
together in front, where they form the chin, but widely separate 
behind; each having a high projecting branch, the coronoid p>rocess 
(cp), for the attachment of the jaw-muscles, and an articular pro- 
cess, the condyle (cd), which forms part of the hinge on which the 
jaw works. This hinge is generally transverse to the general 
