134 



ANATOMY FOR NURSES 



[Chap. VIII 



the passages that communicate with the exterior. These 

 jxissages are subject to the contact of foreign substances, which 

 are introduced into the body, and waste materials, which are 

 expelled from the body. The mucus which it secretes is a thicker 

 and more sticky fluid than either serum or synovia, and by coating 

 the surface lessens the possibility of irritation from food, waste 

 materials, or secreted substances. The cilia of the respiratory 

 tract also assist in the function of protection. 

 They keep up an incessant motion, and thus 

 carry mucus toward the outlet of these pas- 

 sages. Dust and foreign materials usually 

 become entangled in the mucus and are 

 forced out with it. 



(2) The redness of mucous membranes is 

 due to their abundant supply of blood. The 

 small blood-vessels which convey blood to 

 the mucous membranes divide in the sub- 

 mucous tissue, and send smaller branches 

 into the corium, where they form a network 

 of capillaries just under the basement mem- 

 brane. The lymphatics also form networks 

 in the corium, and communicate with larger 

 Fig. 93. — An Jntes- vessels in the submucous tissue below. 

 :r,^nI;'''^Tpith'::iir; (3) The modifications of mucous mem- 

 b, h, capillary network ; brane, such as the valvulre conniventes, pa- 



d, lacteal vessel. . , , .,,. i i i> i i> 



piUfe, and villi, are largely tor the purpose ot 

 increasing the surface for absorption, and also to enable it to 

 carry more blood-vessels and lymphatics. 



CUTANEOUS MEMBRANE 



By this term is indicated the membrane which covers the body 

 and is commonly spoken of as skin. It is a complex structure, 

 iind has several functions in addition to serving as a protective 

 covering for the deeper tissues lying beneath it. It will be more 

 fully considered in Chapter XVIII. 



GLANDS 



A gland is a secreting organ, or an organ which abstracts from the 

 blood certain materials and makes of them a new substance. 



