272 



THE DIGESTIVE SYSTEM 



of the esophagus, and including the musculature of the stomach 

 and intestines, the muscle is entirely of the non-striated or smooth 

 variety. In the pharynx and upper third of the esophagus, the 

 striated or voluntary type of muscle is exclusively found. In the 

 mid-portion of the esophagus both striated and non-striated muscle 

 occur in varying proportions, occasional striated fibres being found 

 even in the lower third of the organ. 



The Submucous Coat consists of loose areolar tissue, and serves 

 for the support of the larger blood and lymphatic vessels which 



supply this coat and the 

 mucosa. A second plexus 

 of nerve fibres, similar in 

 structure to the intra- 

 muscular plexus, is found 

 in the deeper layers of the 

 submucosa, and is known 

 as the plexus of Meissner. 

 Its nerve trunks and gan- 

 glia are somewhat smaller 

 than those of the plexus 

 of Auerbach. The plexus 

 of Meissner supplies the 

 muscular and glandular 

 tissues of the mucous 

 membrane. 



The Mucous Membrane or mucosa of the gastro-intestinal tract 

 contains four typical structures, (1) an internal lining epithelium; 

 (2) the muscularis mucosse which forms the outermost layer ; be- 

 tween these is (3) a tunica propria or corium of diffuse lymphoid 

 or areolar tissue, which serves chiefly for the support of (4) the 

 secreting glands. 



The muscularis mucosce usually consists of a double layer of 

 involuntary or smooth muscle, the outer being longitudinally, the 

 inner transversely or circularly disposed. This layer is most highly 

 developed in the esophagus. 



The tunica propria consists of loose areolar or reticular tissue 

 whose volume is in inverse proportion to that of the secreting 

 glands. It is most abundant in the esophagus. In the stomach 

 and intestines it is considerably infiltrated by lymphatic corpuscles 

 and often contains diffuse lymphoid tissue. Small lymphatic 

 nodules are also found in the deeper part of this membrane ; they 



FIG. 226. SURFACE VIEW OF AUERBACH'S INTRA- 

 MUSCULAR NERVE PLEXUS, FROM THE ESOPHAGUS 

 OF A CAT. 



Methylen blue, x 40 to 50. (After De Witt.) 



