a
middle partition, the nasal septum. Outside the skull, on its wings, is
a flask-like bone, the bulla tympani (b. in Figures 2 and 3), protecting
the middle ear, and from above this there passes an arch, the cheek
bone (ju. in Figures 1, 2, and 3), to the upper jaw, forming in front the
bony lower protection of the cavity containing the eye, the orbit. The
cheek arch, nasal passage, and jaws, form collectively the "facial
apparatus," as distinguished from the cranium, and the whole skull is
sometimes referred to as, the "cranio-facial apparatus." Two
eminences for articulation with the atlas vertebra, the condyles (c.), lie
one on each side of the lower boundary of the foramen magnum.

Section 87. The floor of the cranium consists of a series of cartilage
bones, the basi-occipital (b.o.), basi-sphenoid (b.sp.), pre-sphenoid
(p.sp.), and in front, the ethmoid (eth.), which sends down a median
plate, not shown, in the figure, to form the nasal septum between right
and left nasal passages. Like extended wings on either side of the
basi-occipital are the ex-occipital (e.o.) (the bone is marked
in Figure 4, but the letters are a little obscured by shading).
Similarly the ali-sphenoids (a.s.), are wings to the basi-, and the
orbito-sphenoids (o.s.), to the pre-sphenoid bone (p.sp.). Between the
ex-occipital and ali-sphenoid there is wedged in a bone, the periotic
(p.o.) containing the internal ear (Section 115). Above the foramen
magnum the median supra-occipital bone completes what is called
the occipital arch. A pair of parietals (pa.) come above the
ali-sphenoids, and a pair of frontals (f.) above the orbito-sphenoids. At
the side the brain case is still incomplete, and here the aquamosal
(sq.) enters into its wall. In the external view (Figure 3) the bulla hides
the periotic bone from without. The student should examine all four
figures for these bones before proceeding.

Section 88. The outer edge of the upper jaw and the cheek arch are
made up of three paired bones. First comes the premaxilla (p.m.)
(not p.m.1 or p.m.4), containing in the dog, the three incisors of either
side. Then comes the maxilla, bearing the rest of the teeth.* The jugal
or malar (ju.) reaches over from the maxilla to meet a zygomatic
process (= connecting outgrowth) (z.p.) of the squamosal bone.

* In the dog a sabre-like canine (c.), four premolars (p.m.1 and
p.m.4) and two molars (m.1 and m.2).

Section 89. In the under view of the sk