OKGANS OF DIGESTIOX. THE MOUTH. 779 



SECTION VI. SPLANCEDTOLOGY. 



UNDER the division Splanchnology will be described those organs of the 

 body which have not found a place in any of the foregoing parts of the 

 work. These consist of the organs of digestion, the organs of respiration, 

 the urinary organs, and the organs of generation. 



ORGANS OF DIGESTION. 



The digestive apparatus includes that portion of the organs of assimilation 

 within which the food is received and partially converted into chyle, and 

 from which, after the chyle has been absorbed, the residue or excrement is 

 expelled. It consists mainly of a tubular part, the alimentary canal, to- 

 gether with various glands of which it receives the secretions. 



The alimentary canal is a long membranous tube commencing at the 

 mouth and terminating at the anus, composed of certain tunics or coats, and 

 lined by a continuous mucous membrane from one end to the other. Its 

 average length is about thirty feet, being about five or six times the length 

 of the body. Its upper extremity is placed beneath the base of the skull, 

 the succeeding portion traverses the thorax, and by far the greater part is 

 contained within the cavities of the abdomen and pelvis. 



The part situated above the diaphragm consists of the organs of mastica- 

 tion, insalivation, and deglutition, and comprises the mouthy with the teeth 

 and salivary glands, the pharynx, and the oesophagus or gullet. The 

 remainder includes that part of the canal which is more immediately en- 

 gaged in the digestive process, in absorption, and in defecation, as the 

 stomach and the small and large intestine. The glands which are most 

 intimately connected with digestion consist of those very numerous smaller 

 glandular organs which are situated in the mucous membrane of the alimen- 

 tary canal, and the larger glands, such as the pancreas and liver, whose 

 ducts open within the canal. 



THE MOUTH. 



The mouth, or, more definitely, the buccal cavity, is the space included 

 between the lips and the throat. Bounded by the lips, cheeks, tongue, and 

 the hard and soft palate, it communicates behind with the pharynx through 

 an opening called the fauces (isthmus faucium). The cavity of the mouth 

 is lined throughout by a mucous membrane, which is of a pink rosy hue 

 during life, but pale grey after death, and which presents peculiarities of 

 surface and structure to be noticed hereafter. 



The lips and cheeks are composed of an external layer of skin, and of a a 

 internal layer of mucous membrane, together with muscles, vessels, and 

 nerves already fully described in other parts of this work, some areolar 

 tissue, fat, and numerous small glands. The free border of the lips is pro- 

 tected by a dry mucous membrane, which becomes continuous with the 

 skin, is covered with numerous minute papillae, and is highly sensitive. On 

 the inner surface of each lip, the mucous membrane forms a fold in the 

 middle line, connecting the lip with the gums of the corresponding jaw. 

 These are the frcena or frcenula of the lips : that of the upper lip is much 

 the larger. 



Numerous small glands, called labial glands, are found beneath the 



