ni 



brane, wliich is richly supplied with blood vessels. 

 This membrane is called the mucoun membrane, 

 and from it is secreted by the glands which n 

 tains a viscid substance called mucus |f tin- 

 linger be thrust into the bock of tin- mouth. and 

 tin- mucous membrane gently Hcra|>e<l, the fluid 

 which will adhere to the linger in seen to be vi 

 it is secreted by the glands of the mouth. Not 

 only mucus, but many other substances useful in 

 digestion are formed by little glands in the mucous 

 membrane, so that the whole digestive system is 

 bathed during digestion with lluid having a diges- 

 tive action on the food. In addition there are 

 other glands, such as the salivary, the liver, and 

 the pancreas, which we may look upon an glands 

 of the mucous membrane which have enormously 

 developed. To so great an extent have they in 

 creased in size that they have got far outside the 

 digestive system, and have become situated in neigh- 

 bouring parts of the body, only connected with t In- 

 digestive system by their ducts or elongated mouths. 



Fig. 1. Section through Mouth, Nose, Ao. : 

 a, sphenoid bone ; 6, Eustachiau tube ; e, soft palate ; rf, uvula ; 

 e, nasal passage ; /, upper Jaw ; g, lower jaw ; h, epiglottis ; 

 m, mouth. 



Through these ducts their secretions, like that 

 of the microscopic mucous gland, pour into the 

 cavity of the digestive system. Outside the mucous 

 coat we have the muscular coat, the function of 

 which is to move the food onwards in it- course, 

 and to mix it with the digestive juices. In the 

 mouth, throat, and the upper part of the gullet, 

 the muscles which move the food onwards, as in 

 swallowing, are, when examined by the micro-scope , 

 seen to be transversely striped, amOikc other striped 

 muscles their contraction is rapid. In other p.-in- 

 of the digestive system, however, the muscular coat 

 consists of smooth muscle, ami like all other 

 smooth muscles this coat contract** slowly. < >u 

 this account the food rapidly swallowed panes 

 very slowly along the rest of the digestive system. 



Having shown that the digestive system is a mueo- 

 muscular tube, we may now consider it more in 

 detail. The mouth (fig 1, m) is lined with mucous 

 membrane, and into it is poured the secretion of 

 three pairs of salivary glands the parotids, situ- 



ated in front of tin* car; the mibmaxillarv, within 



the an-le <*f tin- lower jaw ; and the MuhlinipisJ. 

 under tin- ton-ue. Tl,e mouth in moot animal* I* 

 provided \\ith hard tissue* teeth, hem If for UM 

 MihdiviMon of food la-tun- it i nwallowrd. Vege- 

 table feeders, eating tough grnin, root*, and fibres, 

 have large molar or pindin- teeth. while tli ear* 



llivora have these Millie teeth ino.lilie.1 MI 



present a cut tin;: edge, with which and their 

 pointed canines meat is torn and nit into 

 pieces, which are then swallowed (see TKKTHI. 

 The mucous membrane of the mouth in covered 

 externally by the muscle* of the cheek and 

 lips. Into its cavity the m-iwular tongue pro;. 

 On looking into the moiit.i with a tool 

 one sees back into the throat. The entrance to 

 the throat will be olwwrved to be Iwunded at the 

 sides by two muscular curtains paiwing downwards 

 obli(|iiely to the sides of the root of the tongue. 

 These are termed the anterior pillar* of the fauces, 

 and Ix'hind them, one on each side, are manses of 

 lymphoid tissue, Mihject to enlargement, called 

 t he tonsils. .-\|MI\ e. another curtain han-- down. 

 It is called the soft palate, and separates* the mouth 

 from the hinder part of the nasal cavity. Project- 

 ing from its centre is a little cone called the uvula 

 (fig. 1 ). The cavity of the pharynx, or the interior 

 of the throat, i- another cavitv lined by mucoiu 

 membrane, with muscular walls. These muscles 

 constrict it ( constrictors ). Below, the cavity passes 

 into the gullet or o-sophagus, and in front* of t hi-* 

 tube runs the windpipe which communicate* with 

 the pharynx through 



pharynx 



larynx, 



the larynx, or organ 

 of voice. Food will 

 pa through the 

 pharynx into the 

 gullet ; and air, dur- 

 ing respiration, passes 

 through the pharynx 

 on into the larynx 

 and windnipe; a 

 valve, ca"eo tne epi- 

 glottis, partly closes 

 the aperture of the 

 larynx. The pharynx 

 is common, therefore, 

 both to the digestive 

 system and the re- 

 spirator}' passages. 

 Above, the pharynx 

 communicates, as be- 

 fore descrilied, with 

 the mouth and also 

 with the nose. One 

 can demonstrate this 

 latter fact bv drawing 

 smoke in to the mouth, 

 and expellin- it by 

 the nostrils. This 

 communication is 

 clown! during the act 

 of swallowing, and 

 also during the sing- 

 ing of pure vowel 

 sounds, such as d, OM, 

 and the closure is 

 e ilee ted oh Jelly by the 

 elevation of the soft 

 palate, which acts as 

 a valve. The pharynx 

 communicate* in ad- 

 dition with the mid- 

 dle ear by the Kustachian tubes, and this may 

 lie rendered evident if the mouth and nose be 

 closed, and a violent expiratory effort made at 

 tl- same time. As the pressure of air within the 

 throat is increased, the Eustachian tubes which 





