DIGESTIVE ORGANS AND THEIR ANATOMY. 



277 



tines, is in reality but a single continuous tube with but 

 slight local variations. For this reason a description of the 

 coats of the alimentary canal will apply almost equally well to 



all parts of its course. The alimen- 

 tary canal is made up of four dis- 

 tinct coats. On the outside there 

 is a serous coat, which is in the 

 oesophagus . a' reduplication of the 

 pleura, and in the abdomen a redu- 

 plication of the peritoneum. Next 

 to this thin serous coat is a thick 

 muscular coat consisting of two por- 

 tions ; an outer portion in which the 

 fibres run longitudinally, and an 

 inner portion in which the fibres 

 run circularly. It is not necessary 

 to repeat that these muscle fibres 

 are of the plain involuntary variety. 

 Between the longitudinal and 

 circular muscles there run numer- 

 ous blood-vessels to supply this 

 coat, and there occurs, also, a com- 

 plex network of ganglia, and nerve 

 fibres known as the plexus of A tier- 

 bach. From this plexus the mus- 

 cles are directly innervated. Next 

 to the muscular coat is a sub-mu- 

 cous coat consisting largely of are- 



P ig. 107. DIAGRAMMATIC SECTION 



THROUGH THE COATS OF THE olar tissue, with contained blood- 



STOMACH. (After Mall.) i j -i 1 , j 



vessels and lymphatics and serving 



m, mucous membrane; d, duct . 



of gastric giand; m. m., muscular mainly to bind down to the muscu- 



lar coat the large mucous coat. In 

 this sub-mucous coat there is a 

 second well-developed network of 



ganglia and nerve fibres known as the plexus of Meissner. 



From this plexus the mucous membrane and its glands are 



innervated. The last, and in some ways the most essential 



coat of mucous membrane; s. m., 

 submucous coat; c. m., circular 

 muscles; Lm,, longitudinal mus- 

 cles; s., serous coat. 



