Metazoa Rana. 



277 



FIG. 140. PORTION OF THE WALL OF 

 THE ALIMENTARY CANAL AT THE 

 JUNCTION OF THE STOMACH AND 



SMALL INTESTINE. (Quain.) 



function is to assist by their contraction (and consequent 

 narrowing of the oesophagus) in pushing the food down 

 into the stomach. The wave of contraction that follows the 

 food is known as peristalsis. 



The stomach may be divided into a proximal or cardiac 

 (nearest the heart) portion and a distal or pyloric end. 

 Its wall from within outwards consists of (i) a mucous coat 

 with special glands ; (2) a submucous layer of connective 

 tissue, non- striped muscle, blood-vessels, nerves, and ab- 

 sorbing ducts known as lymphatics ; (3) a non-striped 

 muscular coat, whose fibres 

 are arranged in two layers 

 similarly to those of the 

 oesophagus ; and (4) a con- 

 nective tissue coat formed by 

 the peritoneum. 



The intestine similarly 

 consists of four layers 

 mucous, submucous, muscu- 

 lar, and fibrous (fig. 140). 



A detailed study of the 

 last three of these layers is 

 unnecessary in the present 

 instance, but the principal 

 characters of the mucous layer merit more careful considera- 

 tion. In the case of the stomach it is thick, relatively to 

 the other layers, from the presence of closely packed tubular 

 glands, not unlike the test-tubes used in chemical manipu- 

 lations. The glands (gastric glands) are arranged vertically 

 to the surface of the stomach, and consist of a wall formed 

 of columnar or cubical cells capable of secreting into the 

 cavity of the tubule a digestive fluid known as gastric juice, 

 having for its function the rendering soluble of certain sub- 

 stances in the food chemically known as proteids (p. 26). 

 The glands are surrounded by fine connective tissue, capil- 

 laries, and lacteals prolonged upwards from the submucous 



peritoneum ; me, muscular layer ; mi t 

 layer of submucous tissue ; g,g mucous 

 layer ; /, p } pyloric valve ; z, villi of 

 small intestine. 



