THE MOUTH. 



1107 



aperture of the mouth. It is that portion of the cavity which occupies the interval 

 between the lips and cheeks externally, and the teeth and gums internally 



In the normal resting condition, when the mouth is closed and the lips and the 



teeth are in contact, its cavity is practically obliterated by the meeting of its 



walls and it becomes merely a slit-like interval, with a narrow roof and floor 



by the reflection of the mucous membrane from the deep surface of the 



lips and cheeks to the corresponding gum. This reflection is interrupted in the 



median plane by a small but prominent fold of the mucous membrane, the frenulum 



which connects the back of each lip to the front of the gum. The upper frenulum 



j the better developed, and is readily brought into view by everting the lip The 



frenulum of the lower lip is not always present. 



On the outer wall of the vestibule, opposite the crown of the second upper 

 molar, upon a variably developed eminence, is placed the small opening of the duct 

 of the parotid gland, 



Stylo-glossus 



Stylo-pharyngeus 

 ' Glossopharyngeal 

 nerve 



Deep part of submaxillary gland pulled back 

 / Submaxillary ganglion 



Submaxillary duct (Wharton's) 



Cut edge of mucous membrane 



>Sublingual gland 



Sublingual artery 



Genio- 

 /glossus 



Genio-hyoid 



Lingual artery x 

 Middle constrictor 



*Hypoglossal nerve 

 1 Hyoid branch of lingual artery 



Lingual artery 



FIG. 875. DISSECTION OF SUBMAXILLARY REGION. 



which conveys the 

 saliva from the paro- 

 tid gland to the 

 mouth. 



When the teeth 

 are in contact the 

 vestibule communi- 

 cates with the cavity 

 of the mouth only 

 through the small 

 and irregular spaces 

 left between the op- 

 posing teeth, and 

 posteriorly, on either 

 side, by a wider but 

 variable aperture be- 

 tween the last molars 

 and the ramus of the 

 mandible. 



Advantage is some- 

 times taken of the pres- 

 ence of this aperture for the introduction into the cavity of the mouth of liquid food in certain 

 cases trismus, anchylosis, etc. in which the jaws are rigidly closed. 



On the outer wall of the vestibule, the anterior border of the masseter can be distinctly felt 

 with the finger, when the muscle is thrown into a state of contraction. Still further back, the 

 front of the coronoid process, bearing the lower part of the insertion of the temporal muscle, can 

 also be made out. The spheno-mandibular ligament, which corresponds to, and is felt along with, 

 the anterior border of the internal pterygoid muscle, is distinguishable as a pliant ridge when 

 the finger is carried from the front of the coronoid process behind the last molar tooth into the 

 cavity of the mouth. 



In addition to the duct of the parotid, the ducts of numerous small glands which are embedded 

 in the lips and cheeks open into the vestibule. 



Under normal conditions, as pointed out above, the lips and cheeks lie against 'the teeth and 

 gums, obliterating the cavity of the vestibule, and helping, with the aid of the tongue, to keep 

 the food between the grinding surfaces of the molar teeth during mastication. In facial palsy, 

 however, owing to the paralysis of their muscles, and particularly of the buccinator muscle, the 

 lips and cheeks fall away from the dental arches, and allow the food to pass out from between 

 the teeth and to accumulate in the vestibule. 



Cavnm Oris Proprium. The cavity proper of the mouth is the space situated 

 within the dental arches, extending backwards to the glosso-palatine arches (O.T. 

 anterior pillars of the fauces). Its boundaries consist of a roof, a floor, and a margin, 

 formed by the teeth and gums. The roof is formed by the hard palate and the 

 anterior portion of the soft palate, while the floor is formed by the anterior part of 

 the tongue in the middle, and on each side by the reflection of the mucous membrane 

 from the side of the tongue to the mandible. 



On each side of the tongue, and in front of it, when it is at rest, there is only 

 a slit or sulcus between the tongue and the gums, into which the ducts of the 

 submaxillary and sublingual glands open. 



71 a 



