THE MOUTH. 947 
former, that is, in the deeper part of the submucosa, the coronary artery is 
found a short distance from the free margin of the lip, running to meet its fellow 
of the opposite side. 
The free margin of the Hip is covered by a dry and otherwise modified mucous membrane. 
It begins where the integument changes colour at the outer edge of the lip, and ends posteriorly 
just behind the line along which the two lips meet when closed, where it passes into the ordinary 
moist mucous membrane of the vestibule. It presents numerous simple vascular papilla, and 
its nerves (which are derived from the infra-orbital in the upper lip, from the long buccal at the 
angles, and from the mental branch of the inferior dental in the lower lip) terminate in special 
end organs, hence the acute sensitiveness of this part. In the child, at birth, the margin of the 
lip is divided by a very pronounced groove or fissure into an outer and an inner zone, differing 
considerably in their appearance. 
When the tongue is pressed firmly against the back of the lips and moved about, the labial 
glands can be distinctly felt through the mucous membrane, giving the impression of a knobby 
or irregular surface. The glands, which are about the size of hemp-seeds and can be readily 
displayed by removing the mucous membrane, are more numerous in the lower than in the 
upper lip. Stoppage of their ducts, with the resulting distension of the glands, gives rise to 
“mucous cysts,” a well-known pathological condition. 
It should be remembered, in connexion with epithelioma of this part, that the lymphatics of 
both lips pass down to join the submaxillary lymphatic glands. 
Cheeks (bucce).—The cheeks resemble the lips in structure, being formed of cor- 
responding layers. Superficially is the skin. Under this les the fatty superficial 
fascia of the face, through which Stenson’s duct runs imwards to pierce the 
buccinator; in it also, near the end of the duct, are found four or five mucous 
glands, as large as hemp-seeds. These are known as the molar glands (glandule 
molares); their ducts pierce the cheek and open into the vestibule. Beneath 
this superficial fascia les the buccinator muscle, covered by the thin bucco- 
pharyngeal aponeurosis. Deeper still is the submucosa, which, like that of 
the lips, contains numerous racemose buccal glands (glandule buccales). And 
finally the mucous membrane is reached (Fig. 640). 
An important constituent of the cheek of the infant is the sucking pad (corpus adiposum 
buccze), an encapsuled mass of fat, distinct from the surrounding superficial fascia, which hes on 
the outer side of the buccinator, and passes backwards into the large recess between that muscle 
and the overlying anterior part of the masseter. This fatty mass, which is relatively more 
developed in the child than in the adult, strengthens the cheek, and helps it to resist the effects 
of atmospheric pressure during the act of sucking. In the adult the remains of the pad can be 
distinctly made out under the anterior border of the masseter. 
' Cavity of the Mouth Proper (cavum oris proprium).—This is the space 
situated within the dental arches, which latter, with the gums, separate it from 
the vestibule (Fig. 637), so that the two communicate, when the teeth are in 
contact, only by the irregular interdental spaces, and through the passages behind 
the wisdom teeth already referred to. 
Posteriorly it opens, through the isthmus of the fauces, into the. pharynx 
(Fig. 638). 
Its roof is formed by the hard and the greater part of the soft palate ; whilst 
its floor, in the ordinary resting condition, is entirely occupied by the tongue 
(Fig. 640). If, however, the tip and marginal parts of the tongue be raised, there 
is exposed a limited surface to which the term “ floor of the mouth” or sublingual 
region is more usually applied (Fig. 645). 
The sublingual region (Fig. 645) is covered by the oral mucous membrane which 
is carried across from the deep surface of the gum to the inferior aspect of the 
tongue, with the mucous membrane of which it becomes continuous. When the 
tip of the tongue is raised the membrane forms in the middle line a prominent 
fold, the frenum lingue, stretching from the floor of the mouth to the under surface 
of the tongue. On each side of the frenum, near its junction with the floor, there 
can be readily made out a prominent soft papilla (caruncula sublingualis), on 
which the opening of Wharton’s duct (of the submaxillary gland) may be seen 
(Fig. 643). Running outwards and backwards on each side from this, and oceupy- 
ing the greater part of the floor of the mouth, there is a well-marked ridge (plica 
sublingualis) due to the projection of the underlying sublingual gland, most of the 
ducts of which open near the crest of the ridge. 
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