The =maxilla= is shorter but broader and relatively higher than in the
horse. Its external surface bears instead of the facial crest a rough
=facial tuberosity= (Tuber malare), placed above the third cheek tooth;
a rough curved line often extends from it to the upper part of the malar
bone. The infraorbital foramen—often double—is situated above the first
cheek tooth. The tuber maxillare is small, laterally compressed, and
usually bears a small pointed process (Processus pterygoideus). The
zygomatic process is very small. The interalveolar border is concave,
and there is no alveolus for a canine tooth. The palatine process is
wider, but somewhat shorter than in the horse. It incloses a large
air-space, which is continuous behind with a like cavity in the
horizontal part of the palate bone, forming the =palatine sinus=. This
communicates externally (over the infraorbital canal) with the maxillary
sinus; in the macerated skull it communicates with the nasal cavity by a
large oval opening, which is closed by mucous membrane in the fresh
state. A median septum separates the two palatine sinuses. The alveoli
for the cheek teeth increase in size from before backward. The maxillary
sinus proper is small and is undivided. The maxillary foramen is a
narrow fissure, deeply placed at the inner side of the lacrimal bulla.
The maxilla takes no part in the formation of the palatine canal.
Sutural (or Wormian) bones may be found at its junction with the
lacrimal and malar bones.
The body of the =premaxilla= is thin and flattened, and has no alveoli,
since the canine and upper incisor teeth are absent. A deep notch takes
the place of the foramen incisivum. The nasal process is short, convex
externally, and is not closely attached to the nasal bone; the space
between the two processes is greater than in the horse. The palatine
process is narrow and is grooved on its nasal surface for the septal
cartilage and the vomer. The palatine cleft is very wide.
The =palatine bone= is very extensive. The =horizontal part= forms
one-fourth or more of the hard palate. The anterior palatine foramen
opens near the junction with the maxilla, about half an inch from the
median palatine suture and crest. =Accessory palatine foramina= are also
present. The palatine groove is usually not very distinct. The palatine
canal is formed entirely in this part, and there is no articulation with
the vomer. A rounded ridge occurs on the nasal side of the median
suture. The interior is hollow, forming part of the palatine sinus. The
=perpendicular part= is an extensive, quadrilateral, thin plate, which
forms the posterior part of the lateral wall of the nasal cavity and in
part bounds the narrow posterior nares. Its internal surface is nearly
flat, and is smooth and free, except behind, where it is overlapped by
the pterygoid bone. The external surface is attached to a small extent
to the pterygoid process behind, and is free elsewhere. The
sphenopalatine foramen is a long elliptical opening, formed by a deep
notch in the upper edge of the palate bone and completed by the ethmoid
and sphenoid. The edge behind this foramen articulates with the orbital
wing of the sphenoid, not the frontal as in the horse.
[Illustration: