276 STUDIES IN ADVANCED PHYSIOLOGY. 



But the sense of taste is most acute on the third form of 

 papillae known as the circumvallate papilla. These are 

 the largest of all, and may readily be seen on the back of 

 the tongue, where they are arranged in a V-shaped way, 

 with the open end of the V forwards. There are about a 

 dozen individual circumvallate papillae in this V. These 

 papillae do not project materially above the surface of the 

 tongue, but seem to be set down in the mucous membrane 

 of the tongue, being surrounded with a kind of moat not 

 unlike the moat of mediaeval castles. In the walls of this 

 moat, both outer and inner, are found special taste bulbs, 

 which will be described later, and which seem especially 

 concerned in the sensation of taste. The presence of these 

 acute taste bulbs at the base of the tongue explains the 

 familiar fact that foods are most sapid at the instant they 

 are being swallowed. Possibly the explanation of this is 

 that with animals at least, and possibly with man, it serves 

 as an inducement to the swallowing of food. 



On the back of the tongue just at the pillars of the throat 

 are the tonsils. These are lymphatic glands about the size 

 of a small bean, and apart from their general function as 

 lymphatic glands they seem to serve in no special way in 

 their position on the tongue. The mucous membrane cov- 

 ering the tonsils is deeply pitted at these points, and the 

 position of the tonsils may be readily recognized by these 

 mucous pits. 



When by the action of the tongue and pharynx the food 

 is swallowed it is carried over the opening leading into the 

 larynx by the epiglottis, a cartilaginous flap which at the 

 moment of deglutition bends down and covers the passage- 

 way to the lungs. The food is thus carried over the epi- 

 glottis and is seized by the involuntary muscles of the gullet 

 or oesophagus and so sent to the stomach. 



3. THE GULLET OR (ESOPHAGUS. 



The alimentary canal, although more or less arbitrarily 

 divided into the gullet, stomach, and small and large intes- 



