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CHAPTER XXIII. 



OF DIGESTION. PREPARATORY PROCESSES! VIZ. PREHENSION, MASTI- 

 CATION, INSALIVATION, DEGLUTITION : THE ANATOMY OF THE OR- 

 GANS CONCERNED IN THESE PROCESSES.* 



IN the present chapter we shall consider the preliminary stages 

 in the function of digestion, under which head may be included all 

 those which precede the entrance of the food into the stomach. 



Of Prehension, or the taking of food into the mouth, little needs 

 be said. It is performed chiefly by the hand, that wonderful instru- 

 ment of man's lower instincts as well as of his higher attributes. 

 The lips and cheeks, as well as the anterior teeth, and the tongue, 

 are also concerned in this function. 



The lips are endowed with great sensibility, derived from the su- 

 perior and inferior maxillary divisions of the fifth pair of nerves, and 

 are covered with largely developed papillae of touch, which receive 

 an abundant supply of blood from the coronary arteries. Along 

 their margin the skin becomes continuous with the mucous mem- 

 brane of the digestive apparatus, which, within these parts, as well 

 as over the rest of the mouth, the pharynx and oesophagus, as far as 

 the stomach, has an epithelium of the scaly variety; this, variety 

 forming the most essential character of that subdivision of the diges- 



* In entering on a consideration of the alimentary processes, a few words 

 may be conveniently introduced regarding the general anatomy of the mucous 

 system, a term under which we include the skin, mucous membranes, and 

 true glands, all of which are continuous with one another, and composed 

 essentially of similar parts. The skin and the glands pertaining to it, as well 

 as several parts of the mucous membranes, have been already minutely de- 

 scribed in treating of the organs of sense. It only remains, therefore, to 

 speak of the great internal mucous tracts, with their associated glands. 



The alimentary mucous membrane commences at the lips, and lines the 

 passages traversed by the food from the mouth to the anus. The principal 

 glands whose ducts open upon it, are the mucous and salivary glands, the 

 pancreas, and the liver. Besides these, its thickness is made up, in the sto- 

 mach and small intestines, of an infinite series of tubular offsets, vertically 

 arranged, pouring their contents on its free surface, and forming an involuted 

 or compound membrane, or a diffused or membranous gland. The respiratory 

 mucous membrane begins at the nostrils, sends processes to the olfactory, the 

 optic, and the auditory organs, and lines the air-passages to their terminations ; 

 numerous mucous glands occur in this tract. Lastly, the genito-urinary mu- 

 cous membrane commences at the genito-urinary orifices, lines the excretory 

 passages pertaining to both functions, and is the essential constituent of the 





