CH. XXXI.] 



THE ALIMENTARY CANAL 



493 



These two main coats (muscular and mucous) are connected 

 together by a loose layer of connective tissue known as the submucous 

 coat. In this the larger blood-vessels are situated which give off 

 branches to the other two coats but more abundantly to the mucous 

 membrane. The submucous coat also contains a nerve plexus called 

 the plexus of Meissner. In the stomach and intestines there is a 

 fourth coat, on the exterior, derived from the peritoneum (serous coat). 

 The secreting glands in the wall of the alimentary canal are : 

 (1) A number of simple little mucous glands in the corium of the 

 mucous membrane of the mouth, pharynx, and oesophagus ; their 

 ducts open on the surface (see fig. 341). 



FIG. 341. Section of the mucous membrane and submucous coat of the oesophagus, 

 showing mucous glands. 



(2) The gastric glands ; these are tubular glands which differ in 

 structure in different regions of the stomach, and which we shall 

 consider at greater length in our description of gastric digestion. 



(3) The glands of the small intestine. Throughout the whole of 

 the small intestine there are a' large number of simple tubular 

 glands (lined with columnar cells) which open between the villi. 

 They are called the crypts of Lieberkiihn. In the first part of the 



