588 



THE DIGESTIVE TRACT. 



In the abdominal cavity, the outermost layer of the digestive 

 tract is formed of connective tissue and lined with endothelia 

 the peritoneum. 



The salivary glands, pancreas, and liver glandular forma- 

 tions which aid in the digestive process are situated along the 

 tract, and empty their secretions into its cavities. 



(1) The Oral Cavity. The lips are composed of a dense, inter- 

 lacing fibrous connective tissue, of which the lower portions are 

 connected with numerous striped muscles, and the upper por- 

 tions produce the papillae, sometimes showing bifurcating apices, 



FIG. 247. PAPILLA FROM THE LIP OF A CHILD. 



CE, columnar epithelium, nearest to the connective tissue ; CF, connective tissue, crowded 

 with plastids ; A, arteriole ; CV, capillary loops ; V, vein. Magnified 600 diameters. 



and arranged in alternating large and small ones. (See Fig. 

 246.) The capillary reticulum of the large papillae is very dense, 

 and can be traced in direct connection with arterioles and veins. 

 The vermilion color of the lips is due to the large number of 

 capillaries. Within the papillae the connective tissue is com- 

 posed of delicate fibers, with comparatively numerous plastids, 

 which usually have the size and appearance of nuclei. (See 

 Fig. 247.) 



