DIGESTION. 49 



By far the most complicated and best developed prehensile instru- 

 ment in animal mechanics is that employed by man the human 

 upper limb. The extreme perfection of all its parts, and particularly 

 of its terminal portion,, the Iiand, makes it admirably fitted, not only 

 for the prehension of food, but also for the execution of all the various 

 caprices and designs of the human will. Thus it not only simply 

 raises the food to the mouth (prehension), but also, with the human 

 intelligence as the real potent factor, aids in the preparation of food 

 by means of fire (cooking). 



Thus we learn that the first real step in digestion is prehension : 

 bringing the food to the mouth. 



THE MOUTH. 



The space included between the lips in front, the pharynx behind, 

 and the cheeks at the side is the mouth. Above the roof of the mouth 

 we have the palate; below, its floor, upon which rests the tongue. 

 The cavity of the mouth, excepting the teeth, is everywhere invested 

 with a highly vascular mucous membrane, with an investment of 

 squamous epithelium. Conical papillae, for the larger part minute 

 and concealed beneath the epithelium, are found. The lips are 

 separated by the oral fissure. They are composed of various muscles 

 converging to and surrounding the oral fissure. The cheeks have a 

 composition similar to the lips, and their principal muscle is the buc- 

 cinator. At their back part they include the ramus of the 

 jaw and its muscles, and usually between these and the buccinator 

 muscle is a mass of soft, adipose tissue. 



Beneath the mucous membrane of the lips and cheeks, there are 

 a number of small, racemose glands, with ducts which open into the 

 mouth. These glands are, in the lips, called labial and, in the 

 cheeks, buccal. They secrete mucus. 



There are two parts to the palate: a hard and a soft palate. 

 The hard palate is deeply vaulted and lined with a smooth mucous 

 membrane, except at its anterior part, where it is roughened by trans- 

 verse ridges. The soft palate is a doubling of the mucous membrane, 

 inclosing a fibromuscular layer, also containing racemose glands. It 

 hangs down obliquely from the hard palate between the mouth and 

 posterior nasal orifices. It is a freely movable partition. The uvula 

 is an appendage like a tongue projecting from the middle of the soft 

 palate, and consists of a pair of muscles inclosed in a pouch of mucous 

 membrane. 



Palate. The palate has two crescentic folds of mucous mem- 



