DIGESTION. 



243 



and towards the end of the tube form the entire coat. The muscular 

 coat is connected with the mucous coat by a more or less developed layer 

 of areolar tissue, which forms the submucous coat (Fig. 183, 7), in which 

 are contained in the lower half or third of the tube many mucous glands, 

 the ducts of which, passing through the mucous membrane (Fig. 183, c) 

 open on its surface. Separating this coat from the mucous membrane 

 proper is a well-developed layer of longitudinal, unstriated muscle (d), 

 called the muscularis mucosce. The mucous membrane is composed of a 

 closely felted meshwork of fine connective tissue, which, towards the sur- 



FIQ. 182. 



FIG. 183. 



FIG. 182. Section of a mucous gland from the tongue. A, opening of the duct on the free sur- 

 face; c, basement membrane with nuclei; B, flattened epithelial cells lining duct. The duct divides 

 into several branches, which are convoluted and end blindly, being lined throughout by columnar 

 epithelium. D, lumen of one of the tubuli of the gland, x 90. (Klein and Noble Smith.) 



FIG. 183. Longitudinal section of the oesophagus of a dog towards the lower end. a, stratinea 

 epithelium of the mucous membrane; 6, mucous membrane proper; c, duct of mucous gland; a, 

 muscularis muscosse; e, mucous glands; /, submucous coat; 0, circular muscular layer; h, inter- 

 muscular layer, in which are contained the ganglion cells of Auerbach; t, longitudinal muscular 

 layer; fc, outside investment of fibrous tissue. Semidiagrammatic. (V. D. Harris.) 



face, is elevated into rudimentary papillae. It is covered with a stratified 

 epithelium, of which the most superficial layers are squamous. The 

 epithelium is arranged upon a basement membrane. 



In newly-born children the mucous membrane exhibits, in many parts, 

 the structure of lymphoid tissue (Klein). 



Blood- and lymph-vessels, and nerves, are distributed in the.walls of 



