98 ELEMENTARY PHYSIOLOGY 



QUESTIONS ON LESSON XVII. 



1. What is a gland ? Give examples of the different kinds of glands. 



2. Describe some of the various forms of glands. 



3. Describe the general character and use of mucous membrane. Mention 



any part of the body where this membrane may be found. 



4. Describe the form, size, and position of each of the chief salivary glands. 



Where are the openings of the ducts of these glands ? 



5. What is the saliva ? Describe its composition. What is its use ? 



6. What quantity of saliva is secreted daily ? Is it always secreted at the 



same rate ? If not, state the circumstances which accelerate or retard 

 its flow ? 



7. What is ptyalinl How would you illustrate the action of ptyalin on 



certain food-substances ? 



LESSON XVIII. 



THE (ESOPHAGUS AND DEGLUTITION. THE STOMACH 

 AND GASTRIC DIGESTION. 



THE oesophagus is the narrowest portion of the alimentary canal, 

 and, although generally described as muscular, it consists of three 

 distinct coats. The outer coat is thick and muscular ; and con- 

 sists of two distinct sets of muscular fibres, some running longi- 

 tudinally, i.e. lengthwise down the tube, and the others passing in 

 a circular direction round it The inner coat is a mucous mem- 

 brane, which, as its name implies, contains mucous glands ; it is 

 drawn up into longitudinal folds, thus increasing the amount of 

 secreting surface. The middle coat consists of a loose filamentous 

 membrane called connective, areolar, or fibrous tissue, which unites 

 the outer and inner coats of the tube. 



After the food has been masticated and thoroughly mixed with 

 the saliva, it is collected into a bolus by the tongue and the 

 muscles of the cheeks, and then passed between the tongue and 

 the palate till it reaches the back of the mouth. This muscular 

 action may be voluntary, but is usually performed uncon- 

 sciously. 



The food must now pass into the pharynx without touching the 

 posterior nares or entering the glottis. This is accomplished as 

 follows : The larynx and pharynx are both raised together and 

 carried forward under the tongue. The glottis is closed by the 

 epiglottis ; and the posterior nares are shut off by the sides of the 

 soft palate. The contraction of the muscles at the back of the 

 mouth torces the food over the epiglottis into the pharynx. The 

 pharynx no\\ contracts above it, and the bolus is forced into the 



