602 



THE POPULAR SCIENCE MONTHLY 



the air-pipe ; and, to keep food and drink from taking the wrong road, 

 there is an effective system of valves. The parts act spasmodically 

 whenever they are irritated by the pressure of solids and liquids. 



Saliva is found in nearly all animals. Its universal office is to lu- 

 bricate the food and so help it to glide easily along the pharynx and 



Fig 1 Median Anteroposterior Section op the Human Face : a, septum of nose, with 

 section of hard palate below it ; b. tongue ; c, section of soft palate ; d, d, lips ; m, uvula ; r, 

 anterior arch or pillar of fauces; i, posterior arch ; t, tonsil; p, pharynx; h, hyoid bone; k, 

 thyroid cartilage n, cricoid cartilage ; s, epiglottis ; v, glottis ; 1, posterior opening of nares ; 

 3, isthmus faucium: 4, superior opening of larynx ; 5, passage into oesophagus ; 6, orifice of 

 right Eustachian tube. 



gullet. This kind of saliva is a glairy mucus, and is the only kind in 

 animals which do not chew the food for example, birds, reptiles, 

 and fishes. As an aid to digestion, the saliva of mammals will be 

 considered later. 



The most astonishing feats in swallowing are performed by the 

 snakes. The boa can certainly swallow a goat or deer. Our common 

 little snakes, the size of a finger, can swallow a large frog, a perform- 

 ance sufficiently remarkable. The process is very slow and tedious, 

 and one would suppose painful. The boa first kills its prey by crush- 

 ing it in its tightening coils, which break down the ribs and limbs and 

 reduce the victim to a shapeless mass. By this horrible proceeding the 

 carcass is gotten into condition to be more easily swallowed. After 

 coating it with mucus, the boa begins the difficult operation of fore- 



