THIRTEENTH LECTURE. 



THE DIGESTIVE APPARATUS WITH ITS GLANDS. 



The digestive apparatus, in its connective-tissue external 

 layers and the muscular middle layers, is certainly of a rela- 

 tively simple nature. The mucous membrane, however, with 

 the immediately adjacent loose connective tissue, and with all 

 which is connected with it, presents an abundance of the 

 most diversified structural relations. 



Let us therefore briefly examine the long canal work, with 

 the varying constituents in its interior. 



The oral cavity contains the already described teeth (p. 73), 

 as well as the tongue. In it open the salivary glands, large 

 racemose organs, and, together with these, a number of 

 smaller associates, the so-called mucous glands. 



From the vascular mucous membrane of the mouth project 

 closely crowded papillae. It is covered by the stratified pave- 

 ment epithelium spoken of at 

 page 30. The latter may here 

 acquire a thickness of 0.45 mm. 

 The submucous connective tissue 

 appears sometimes dense (gums), 

 sometimes loose and extensible 

 (the floor of the mouth). In 

 it lie the bodies of the numer- 

 ous small racemose glands. The 



secretion is mucus ; the cells 



Fig. 130. — Gland vesicles of the palatine 

 gland of the rabbit ; a, rounded, b, an elon- 

 gated acinus. 



form a layer of pale, cubical or 

 low cylindrical elements (Fig. 

 130). They occur as labial, buc- 

 cal, palatine and lingual glands. 



Among the salivary glands the submaxillary has recently 

 undergone an accurate investigation (Pfliiger, Gianuzzi, Hei- 



