212 ANIMAL PHYSIOLOGY. [LESSON 61. 



tongue, above the circumvallate papillae, indicate the mucus-crypts 

 of Leiberkuhn, which are abundant in this situation. 



920. The oesophagus is provided with two layers of muscles ; one 

 longitudinal, the other transverse. 



921. By their united action the food is conveyed to the stomach, 

 and delivered to what is called the cardiac orifice. 



922. In form the stomach very much resembles the bag of a bag- 

 pipe, to which it is generally compared. 



923. It possesses three 

 coats, an internal mucus, a 

 muscular, and an external se- 

 rous coat derived from the 

 peritoneum, or the membrane 

 which lines the muscles of the 

 abdomen. 



924. A figure of the ex- 

 ternal form of the stomach is 

 given (Fig. 335) ; the ossoph- 



agus (a) enters the stomach 

 The human stomach. . v ' 



at the cardiac orifice ; the 



constriction at the other extremity marks the pyloric valve (b) ; and 

 the first of the small intestines, the duodenum, commences on the 

 other side the pylorus (c). 



925. As soon as the food reaches the stomach, it comes in con- 

 tact with agents which exert a chemical influence upon it ; these are 

 the gastric juice, and mucus. Stimulated by the presence of food, 

 the muscles are in incessant action, constantly contracting on it, 

 moving it from side to side, literally churning it. 



926. The combined action of the heat of the stomach, the mus- 

 cular action, and the solvent power of the gastric juice, aided by a 

 peculiar influence of the mucus, reduces the food to its elements, or 

 dissolves it into a pulpy state, called chyme. 



927. In this form it makes application to pass through the py- 

 loric valve, and if there be no solid particles, it is permitted so to 

 do ; but undigested matter is sent back again to be thoroughly re- 

 duced before it can be allowed to go through the valve into the duo- 

 denum. If, however, the food chance to be of an unhealthy or in- 

 digestible character, the stomach soon casts it out, in the same state 

 that it entered the organ, and proceeds to act upon what may remain 

 of a better character. 



