MUCOUS MEMBRANE. 39 



near the month of the follicle in which the hair is 

 lodged. Lastly, in some parts of the skin, par- 

 ticularly the tips of the fingers, the lips, and the tip of 

 the tongue, a beautifully delicate apparatus connected 

 with the sense of touch is formed. 



63. Mucous membrane. Closely allied to the skin 

 in structure, and indeed continuous with it, is a sort 

 of internal skin called mucous membrane, which lines 

 the digestive apparatus from one end to the other, 

 and also the respiratory organs. The mncous mem- 

 brane is modified in structure in every part of its 

 course according to the offices it has to discharge. 

 In some situations the surface is hard and even 

 horny, while in others it is soft like velvet. Almost 

 dry and rigid in some places, in others consisting of 

 glands packed closely together and constantly secret- 

 ing an enormous quantity of fluid. Again, instead 

 of being a secreting surface, a considerable extent 

 is modified to form a highly efficient absorbing 

 apparatus. 



Besides the many tissues and organs already 

 enumerated, several very highly elaborate structures 

 are gradually formed which cannot come into use at 

 all until after birth. The development of these con- 

 tinues to advance for some time, and not only is it 

 doubtful if they attain their most perfect condition 

 before the adult period of life is reached, but it is 

 certain that some of them continue to improve for 

 many years afterwards. 



64. Organ of smell. The organ of smell is in its 

 structure much simpler than the other organs of 

 special sense, but the arrangement of the nervous 

 apparatus is very beautiful. The nerves come quite 

 to the surface, and it is probable that odoriferous par- 

 ticles come into actual contact with nerve tissue. The 

 olfactory mucous membrane in very young animals 

 is a tissue in which the ultimate ramifications of nerve 



