GLANDS 45 



the internal ear (hair cells), in the olfactory mucous 

 membrane*, in the taste-buds of the tongue, and tactile 

 cells in the epidermis. 



9. Glandular Cells. These are found in the pancreas, 

 liver, etc., and their shape varies according to the 

 gland in which they are found. 



Mucous Membranes. All the surfaces of the gastro- 

 intestinal and pulmonary tracts, genito-urinary appar- 

 atus, etc., within the body are covered by epithelial 

 cells, called mucous membranes, These membranes 

 are protected in the various organs by a superficial 

 layer of cells their variety depending on the tissue 

 they are found in which we have described above. 

 Beneath this layer the cells rest upon a delicate base- 

 ment membrane, the next layer is the tunica propria 

 consisting of a layer of fibro-elastic tissue. Within 

 this layer are lodged the capillary bloodvessels, 

 nerves, lymphatic spaces or channels, and, in certain 

 organs, glands and lymphoid tissue. These thin layers, 

 are seen resting on a fourth peripheral layer, called 

 the muscularis mucosse, consisting of involuntary 

 (not under the control of the will), non-striated muscle 

 tissue. This layer is sometimes wanting in some tissues. 

 The above mucous membranes line cavities which 

 communicate with the air. Their cells usually secrete 

 a substance called mucin. 



Glands. Glands are considered under the classifica- 

 tion of epithelial tissues. They are simply various 

 shaped pouches or tubes of mucous membranes grow- 

 ing out from the superficial surface of the tissue in 

 which they are located. All glands are lined with 

 epithelial cells arranged in different groups, and 

 possessing a physiologic function. These groups of 

 cells are the units from which the organs develop 

 their secretions. 



Glands are subdivided into (1) tubular, simple, 

 branched, coiled, compound; (2) tubulo-alveolar ; (3) 

 alveolar, or racemose glands, simple and compound. 



