414 ALIMENTARY CANAL 



the ship reaches port (conditioned reflexes). By means of the 

 taste buds on the tongue, the nature of the cargo is further ascer- 

 tained and appropriate secretions from the sahvary glands take 

 place (reflex). Bitter or saline substances provoke a profuse 

 secretion of watery saliva. Flesh is met by a secretion containing 

 a large proportion of the lubricating material- — mucin. Dry 

 matter causes the flow of a thinner and more watery saliva than 

 moist matter. 



{a) The functions of saliva in the mouth are purely mechanical 

 (par. (c) below). It acts as a lubricant : moistening the surfaces 

 of the mouth and the passage from it ; infiltrating the food mass 

 and so necessitating the expenditure of less energy in milling the 

 food ; and finally covering the outside of the bolus with mucin, 

 thus rendering deglutition easy. Normally, saliva has no chemical 

 action i7i the mouth. It contains a diastatic enzyme, ptyalin, which, 

 however, carries out its action on polysaccharides during the earlier 

 period of digestion in the stomach (q.v.). 



(b) The tongue is a mobile organ lying on the floor of the mouth. 

 It consists mainly of a mass of muscles which are paired. Some 

 of these muscles lie wholly within the tongue (intrinsic), and for 

 the most part, by their contraction, give rise only to alterations 

 in shape. The extrinsic muscles have their point of attachment 

 outside the organ, and so are capable of causing alterations in 

 position as well as in form. 



Intrinsic Muscles. 



1. Superior longitudinal, pulls tip upwards and decreases length of dorsum. 



2. Inferior longitudinal, pulls tip downwards and inwards, i.e. curves 



dorsum. 



3. Vertical, working in conjunction with the transverse they produce 



a concave surface on the dorsum. Acting alone a convex surface 

 is produced. 



4. Transverse. 



Extrinsic Muscles. 



1. Genio-glossus — downwards. 



2. Hyo-glossus — backwards. 



3. Chondro-glossus (not always present) — backwards and downwards. 



4. Stylo-glossus — backwards and towards palate. 



5. Palato-glossus — side to side — continuous with intrinsic transverse. 



The tongue has a threefold duty to perform as a unit of this 

 transport system^ — (a) working in conjunction with the lip- 

 sphincter^ — orbicularis oris, and with the triangidar and other 

 muscles it acts as a suction-plunger ; (/3) diu'ing deglutition it 



