ORGANS 



529 



ALIMENTARY CANAL 



The alimentary canal has already been mentioned as including 

 columnar epithelium and smooth muscle. In most parts at least 

 four layers, with subdivisions, may be distinguished in the wall 

 (Fig. 411). On the inside is the epithelium, often with glandular 



y/LLUS U/tTH M£R^E'S£r 



CENTRAL LACTEAL 



UEBERXUHNE'J FOLLICLE 



':*»: MUSCULy^RIS MUCOS/S. 



M£ISSN£RS PLEXUS 



SUBMUCOSA 



LYMPHATIC PLEXUS 

 C/P.CULAR. MUSCLE 



LYMPHATIC PLEXUS 

 AUEKBACH'S PLEXUS 



LOA/<;jTUD/NAL MUSCLE 



:' ^ .\SEfZOUS COAT 



Fig. 411. — Diagrammatic section through the wall of a mammalian small 

 intestine to show vascular and lymphatic arrangements. — From Yapp, A n 

 Introduction to Animal Physiology, 1939. Clarendon Press, Oxford. After 

 Schaffer. 



developments. Surrounding this is a layer of areolar tissue called 

 the submucous coat, in which run blood vessels and lymphatics, 

 and the autonomic nerve net called Meissner's plexus ; between 

 the submucous coat and the epithelium there is, in the small 

 intestine, a layer of smooth muscle which produces contractions of 

 the villi, or projections into the lumen. Outside the submucous 

 coat is the muscular layer which makes up most of the thickness 



