The maxillary, lacrimal, and turbinal sinuses have been opened, and a
portion of the orbit removed, _a_, Cavity of superior turbinal bone;
_b_, lacrimal sinus; _c_, maxillary sinus; _d_, communication
between maxillary and palatine sinuses; _e_, opening between
maxillary and lacrimal sinuses; _f_, thin osseous bulla; _g_,
lacrimal bulla; _h_, orbit; _1–6_, cheek teeth; _7_, nasal bone;
_8_, premaxilla (nasal process); _9_, maxilla; _9′_, infraorbital
foramen; _10_, frontal bone; _11_, lacrimal bone; _12_, malar bone;
_13_, fissure between nasal bone and maxilla; _14_, temporal bone
(squamous); _15_, external auditory meatus; _16_, styloid or
paramastoid process; _17_, occipital condyle; _18_, palate bone
(perpendicular part); _19_, pterygoid bone (hamulus); _20_, tympanic
part of temporal; _20′_, muscular process of petrous temporal.
(After Ellenberger, in Leisering’s Atlas.)
]
The =maxillary sinus= is excavated chiefly in the maxilla, lacrimal, and
malar, and is not divided by a septum as in the horse. It extends
forward as far as the facial tuberosity, or a little further in old
animals. Its upper limit is indicated approximately by a line drawn from
the infraorbital foramen to the upper margin of the orbit. It is
continued directly backward into the lacrimal bulla to a point nearly
opposite to the bifurcation of the zygomatic process of the malar. It
also extends upward and backward through a large opening into a cavity
formed by the lacrimal, frontal, ethmoid, and turbinal bones, at the
inner side of the orbit.[26] The floor of the cavity is irregular and
the roots of the last three or four cheek teeth project up into it,
covered by a plate of bone. The sinus communicates with the palatine
sinus freely over the infraorbital canal through an oval opening about
two to three inches (ca. 5 to 7.5 cm.) long. Above this it communicates
by a shorter and much narrower opening with the middle meatus nasi.
The =palatine sinus= is excavated in the hard palate, and is separated
from that of the opposite side by a median septum. It extends from the
posterior border of the palate to a plane an inch or more (2.5 to 3 cm.)
in front of the first cheek tooth. As mentioned above, there is a large
communication with the maxillary sinus over the infraorbital canal, so
that the cavity is sometimes regarded as a part of that sinus. The large
defect in the bony roof of the sinus is closed by two layers of mucous
membrane in the fresh state. The palatine canal passes obliquely through
the posterior part of the sinus.
The =sphenoidal sinus= is almost entirely in the sphenoid bone and does
not communicate with the palatine and maxillary sinus. It has one or two
openings into the ventral ethmoidal meatuses. There is no cavity in the
perpendicular part of the palate bone.
There are several small air-cavities between the lateral mass of the
ethmoid and the anterior part of the frontal sinus, which communicate
separately with ethmoidal meatuses.