870 



THE ORGANS OF DIGESTION. 



externally by integument and internally by mucous membrane, between which are 

 found the Orbicularis oris muscle, the coronary vessels, some nerves, areolar tissue, 

 and fat, and numerous small labial glands. The inner surface of each lip is connected 

 in the middle line to the gum of the corresponding jaw by a fold of mucous membrane, 

 ihefrcenum labii superioris and inferioris the former being the larger of the two. 



The labial glands are situated between the mucous membrane and the Orbicu- 

 laris oris round the orifice of the mouth. They are rounded in form, about the 

 size of small peas, their ducts opening by small orifices upon the mucous mem- 

 brane. In structure they resemble the salivary glands. 



The cheeks form the sides of the face and are continuous in front with the lips. 

 They are composed externally of integument, internally of mucous membrane, 

 and between the two of a muscular stratum, besides a large quantity of fat, areolar 

 tissue, vessels, nerves, and buccal glands. 



The mucous membrane lining the cheek is reflected above and below upon the 

 gums, where its color becomes lighter ; it is continuous behind with the lining mem- 



Opening of nasal duct. 



Bristle passed through 

 Stenson's duct. 



FIG. 466. Sectional view of the nose, mouth, pharynx, etc. 



gums, and it is continuous behind with the lining membrane of the soft palate. 

 Opposite the second molar tooth of the upper jaw is a papilla, the summit of which 

 presents the aperture of the duct of the parotid gland. The principal muscle of 

 the cheek is the Buccinator, but numerous other muscles enter into its formation 

 viz., the Zygomatici, Risorius Santorini, and Platysma myoides. 



The buccal glands are placed between the mucous membrane and Buccinator mus- 

 cle : they are similar in structure to the labial glands, but smaller. Two or three of 

 larger size than the rest are placed between the Masseter and Buccinator muscles ; their 

 ducts open into the mouth opposite the last molar tooth. They are called molar glands. 



Ihe gums are composed of a dense fibrous tissue closely connected to the 



