78 TOPOGRAPHICAL ANATOMY OF THE 



faucium, by which it communicates with the pharynx. The isthmus 

 faucium is circumscribed by the soft palate dorsally, the glosso-palatine 

 arch laterally, and the tongue ventrally. The cavity of the mouth is 

 bounded in front by the lips, and laterally by the cheeks. The roof is 

 formed by the hard and soft palates, and the posterior limit is defined 

 by the soft palate, where it lies in contact with the most posterier part of 

 the tongue. The ventral boundary is constituted by the tongue and 

 the "floor of the mouth " or sublingual region. 



The mouth cavity comprises two parts : (1) the vestibule (vestibulum 

 oris) ; and (2) the mouth cavity inoper (cavum oris proprium). 



The vestibule consists of a narrow space between the lips and cheeks 

 on the one hand and the teeth and gums on the other. The mucous 

 membrane reflected from the lips and cheeks to the incisive, maxillary 

 and mandibular bones forms its upper and lower boundaries. In front 

 the vestibule communicates with the exterior by an elongated opening 

 (rima oris) between the lips. Communication between the vestibule 

 and the mouth cavity proper is effected through the spaces between the 

 incisor, canine and cheek-teeth, and behind the last cheek-tooth. Into 

 the vestibule, on each side, open the ducts of the parotid and buccal 

 glands. 



The mouth cavity proper is contained within the dental arches, by 

 which, and the gums connected therewith, it is bounded in front and on 

 each side. Behind it communicates with the cavity of the pharynx 

 through the isthmus faucium. The roof of the cavity is formed by the 

 hard and soft palates, while the floor is formed by the tongue and the 

 mucous membrane extending therefrom to the mandible. Into this 

 part of the mouth open the ducts of the sublingual and submaxillary 

 glands. 



The lips (Labia). — A preliminary inspection of the lips was made 

 at an earlier stage (page 33). They must now be examined more 

 thoroughly. 



Each lip may be regarded as consisting of four laj'ers : — (1) The 

 outer surface is covered by skin that is closely adherent to the under- 

 Ijdng muscular layer. On it two, or possibly three, kinds of hair may 

 be distinguished. The most numerous are fine and short, and resemble 

 those over the face in general. Sometimes much longer hairs, also 

 moderately fine in quality, form a veritable moustache on the upper 

 lip. Long and strong tactile hairs (sinus-hairs) are fairly abundant, 

 these passing through the entire thickness of the skin, to be embedded 

 in the underlying muscle. (2) A muscular layer constitutes the greater 

 part of the whole thickness of the lip and contains a sphincter muscle 



