64 
OSTEOLOGICAL GALLERY. 
bones, the turhinal bones (^), and forming the narial or olfactory 
chamber. Below this chamber, and forming in part its floor and 
walls, is the jaw, composed of the maxillary and premaxillary bones 
[nix andj5m<r), in which are implanted the upper teeth, the lower 
ones being similarly fixed along the upper edge of the mandible. 
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 (/r), and by the small and narrow nasal 
bones (na), placed between the upper edges of the maxillary bone 
where it rises to form the side- walls of the olfactory chamber. 
External to these bones are the zygomatic arches (fig. 26, zy)^ which 
serve to support and protect the masticatory muscles, and which 
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 supraoccipital (so), a pair of exoccipitals (exo), and the basi- 
occipjital (bo), surrounding the large opening through which the 
spinal cord passes — the foramen magnum. 
The mandible consists simply of a pair of solid bones, joined 
together in front where they form the chin, but widely separate 
behind, each with a high projecting branch, the coronoid process 
(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 
mandible works. This hinge is generally transverse to the general 
axis of the skull ; but in some Orders, such as the Rodents, the 
condyle is lengthened antero-posteriorly, and works in a correspond- 
ing longitudinal depression in the base of the skull. 
The hyoid apparatus (h) consists of a series of small bones 
suspended from the posterior part of the cranium, and supporting 
the larynx and root of the tongue. 
The dentition of Mammals is of two kinds. In some few forms, 
known as ^niomodout,^^ all the teeth are of one type or pattern 
as in the Sloths, /Vrmadilloes, Dolphins, &c. ; the remainder, or 
^Mieterodont Mammals, which form the great majority, are pro- 
vided with teeth of several different types. Thus in the Dog^s skull 
(fig. 27) the three small teeth fixed on each side in the premaxilla 
{pmx) are the incisors, or cutting-teeth (i) ; next follows a long and 
powerful tooth, known as the canine (c). Behind this there are 
