The mucous membrane is retained. The septum nasi is removed. _a_,
Superior meatus; _b_, middle meatus, with _b′_ and _b″_, its upper
and lower divisions; _c_, inferior meatus; _d_, superior turbinal;
_e_, superior turbinal fold; _f_, inferior turbinal; _g_, alar fold;
_h_, inferior turbinal fold; _i_, lateral mass of ethmoid
(ethmoturbinals); _i′_, large ethmoturbinal or middle turbinal; _k_,
frontal sinus; _l_, sphenoidal sinus; _m_, cranial cavity; _n_,
palatine sinus; _o_, nasal bone; _o′_, parietal cartilage; _p_,
palate process of maxilla; _q_, palate bone (horizontal part); _1_,
sphenoid bone; _2_, _3_, inner and outer plates of frontal bone;
_4_, _4′_, outer and inner plates of parietal bone; _5_, _5′_,
occipital bone; _5″_, condyloid and hypoglossal foramina; _6_,
paramastoid or styloid process; _6′_, occipital condyle; _7_,
petrous temporal bone; _7′_, internal auditory meatus; _8_, squamous
temporal bone; _9_, muscular process; _10_, pterygoid bone
(hamulus). (After Ellenberger, in Leisering’s Atlas.)
]
The =pterygoid bone= is wider than in the horse, and forms the greater
part of the lateral boundary of the posterior nares. Its outer surface
is almost entirely united to the palate bone and the pterygoid process,
but a small part is free in the pterygo-palatine fossa. The hamulus is
distinctly hook-like, thin, and sharp.
The =nasal bone= is little more than half the length of that of the
horse. It is straight in its length, but strongly curved from side to
side. It does not fuse laterally with the adjacent bones, even in old
age. The posterior extremity is pointed and fits into the notch between
the frontal bones. The anterior end is broader, and is divided into two
parts by a deep notch. In old animals there is a small extension of the
frontal sinus into this bone.
The =lacrimal bone= is very large. The extensive facial part is concave
in its length, and bears no lacrimal tubercle. The orbital margin is
marked by several notches. The orbital part forms below the remarkable
=lacrimal bulla=; this is a large and very thin-walled protuberance,
which bulges backward into the lower part of the orbit, and contains an
extension of the maxillary sinus. The lacrimal fossa is small, and is
just behind the orbital margin.
The =malar bone= is relatively long. The facial surface is extensive; it
bears a curved crest (Crista facialis) just below the orbital margin,
and below this it is concave from above downward. The zygomatic process
divides into two branches; of these, the frontal process turns upward
and backward and joins the supraorbital process of the frontal bone; the
temporal process continues backward, and is overlapped by the zygomatic
process of the temporal bone, completing the zygomatic arch.
The =superior turbinal bone= is less cribriform and fragile than in the
horse, and is thickest in its middle, small at either end. It is
attached to the turbinal crest of the nasal bone, and curves downward,
outward, and upward to be applied outwardly to the frontal and lacrimal
bones. It thus incloses a cavity which communicates with the middle
meatus nasi. (In the macerated skull it opens into the frontal sinus,
but this communication is closed by mucous membrane in the fresh state.)
The =inferior turbinal bone= is shorter but much broader than in the
horse. It is attached to the maxilla by a basal lamella about an inch
(ca. 2 to 3 cm.) wide, which slopes downward and inward. At the inner
edge of this it splits into two plates which are rolled in opposite
directions, and inclose two separate cavities, subdivided by several
septa. The upper one opens into the middle meatus, the lower one into
the inferior meatus nasi.
The =vomer= forms a wider and deeper groove than in the horse. Its
anterior end rests in a groove formed by the ends of the palatine
processes of the premaxillæ. The anterior third of its thin lower edge
fits into the nasal crest of the maxilla; behind this it is free and
separated by a considerable interval from the nasal floor.
[Illustration: