_1_, Raphé palati; _2_, ridges of palate; _3_, anterior end of soft
palate, showing orifices of ducts of palatine glands.
]
=Structure.=—The soft palate consists of: (1) The oral mucous membrane,
continuous with that of the hard palate; (2) the =palatine glands=
(Glandulæ palatinæ), which form a layer about half an inch in thickness;
(3) the aponeurotic and muscular layer; (4) the pharyngeal mucous
membrane, continuous with that of the nasal cavity.
The =muscles= proper to the soft palate are the azygos uvulæ, the
levator palati, and the tensor palati.
The =azygos uvulæ= (M. palatinus) consists of two small muscular bundles
which lie together at the median line. It is attached through the medium
of the palatine aponeurosis to the palatine arch, and terminates near
the free edge of the soft palate. Its action is to shorten and raise the
soft palate.
The =levator palati= (M. levator veli palatini) arises from the muscular
process of the petrous temporal bone and from the Eustachian tube, and
passes forward and downward externally to the latter, to spread out on
the pharyngeal surface of the soft palate. It raises the soft palate,
thus closing the posterior nares during deglutition.
The =tensor palati= (M. tensor veli palatini) is larger than the
levator, and is fusiform and flattened. It arises from the muscular
process of the petrous temporal bone and the Eustachian tube, and passes
forward external to the levator. Its tendon is then reflected around the
hamulus of the pterygoid bone, being held in position by a fibrous band
and lubricated by a bursa. It turns inward and expands in the
aponeurosis of the soft palate. It tenses the soft palate.
=Vessels and Nerves.=—The blood-supply of the soft palate is derived
from the internal and external maxillary arteries. The nerves come from
the trigeminus, vagus, and glosso-pharyngeal nerves.
[Illustration:
FIG. 240.—CROSS-SECTION OF HEAD OF HORSE JUST IN FRONT OF FACIAL
CREST.
_1_, Cavity of superior turbinal; _2_, cavity of inferior turbinal;
_3_, cavum oris; _4_, _4_, genio-glossi; _5_, _5_, genio-hyoidei;
_6_, hyo-glossus; _7_, upper, _7′_, lower fourth cheek tooth. Line
to facial artery crosses zygomaticus.
]
The =floor= of the mouth in its anterior part is free and is formed by
the body of the mandible, covered by mucous membrane. The remainder is
concealed by the attached portion of the tongue, with the exception of a
narrow space on each side of the latter. About opposite the canine tooth
on each side is a papilla, the =caruncula sublingualis=, through which
the duct of the submaxillary gland opens. Just behind these papillæ is a
median fold of mucous membrane which passes to the under surface of the
tongue, constituting the =frenum linguæ=. On either side are the
sublingual crests, which extend from the frenum to the level of the
fourth cheek tooth. The crest presents numerous small papillæ, through
which open the ducts from the subjacent sublingual gland.[79] Behind the
last tooth a vertical fold of the mucous membrane passes from upper to
lower jaw. This is termed the plica pterygomandibularis: it contains a
ligament of like name.
The =isthmus faucium= is the orifice of communication between the mouth
and the pharynx. It is bounded above by the soft palate, below by the
root of the tongue, and laterally by the anterior pillars of the soft
palate. It is long, relatively small, and not very dilatable in the
horse, and is closed by the soft palate under normal conditions, except
during deglutition.