i 3 4 PHYSIOLOGY KOR BEGINNERS . n \i . 



from side to side in chewing. The movements are produced 

 by the contraction of the muscles passing from the fixed bones 

 of the skull to the flat side-pieces of the lower jaw bone. The 

 food thus broken up and mixed with saliva is then collected 

 by movements of the tongue (which is chiefly composed of 

 muscle) and of the cheeks, into a mass and thrust to the back 

 of the mouth ; the soft palate is then raised, and as the mass 

 passes the fauces, the sides of the passage, the muscular 

 pillars of the fauces as they are called, contract on it and 

 squeeze it on into the pharynx. The muscular walls of the 

 pharynx then contract on the mass and squeeze it along the 

 pharynx, past the glottis closed by the epiglottis, into the 

 cesophagus, and this, which has also muscular tissue in its 

 wall, carries it on in the same way into the stomach. Fluid is 

 swallowed in a similar manner, by muscular contraction of the 

 walls of the pharynx and cesophagus. For this reason a 

 horse can swallow with its head lower than its stomach, and 

 it is possible for a man to drink when " standing on his head." 



The Lining of the Alimentary Canal. The alimentary 

 canal is lined by what is called mucous membrane. A 

 mucous membrane consists of one and sometimes of more 

 than one layer of cylindrical, cubical, or roundish cells closely 

 packed together, underneath which lies loose connective tissue, 

 consisting of fibres and cells and containing blood-vessels and 

 nerves. The part formed by the cubical or cylindrical cells 

 is called an epithelium. The epithelium of the greater 

 part of the alimentary canal, of the stomach and the small 

 and large intestine, consists only of a single layer of cells, 

 many of which are of a peculiar nature in so far as they form 

 a slimy material called mucus. The epithelium of the 

 mucous membrane of the mouth and cesophagus consists on 

 the other hand of a layer of cubical cells, covered by four or 

 five rows of cells which gradually become flatter towards the 

 free surface. Such an epithelium is called a squamous epi- 

 thelium. The connective tissue layer with its blood-vessels 

 intervenes between the epithelium and the muscles of the 

 cheeks and other parts on which the mucous membrane lies. 



Glands and Secretion. Here and there in the mucous 

 membrane of the mouth, passing through the epithelium 

 into the deeper connective tissue layer, is a minute tube, 



