188 ANIMAL PHYSIOLOGY. [LESSON 53. 



have hitherto been lightly dealt with, notwithstanding their impor- 

 tant influence on the great question under discussion, have been re- 

 served designedly until the salient points in regard to the ultimate 

 structure of the (apparently) most important organs had been dis- 

 posed of; and because it was deemed more advisable to take such 

 subjects specially, in connection with the nutrition of man. These 

 are, the structure of the teeth, the structure, but more especially the 

 function of the salivary glands, and the properties of the gastric juice 

 and mucus. 



LESSON LIU. 



' / 



THE STRUCTURE OF THE TEETH. 



809. The teeth claim priority, and, reversing the order of arrange- 

 ment hitherto pursued, in which the lower animals have served as 

 the basis for the consideration of more complicated structures, de- 

 voted to the performance of a kindred function in the higher forms 

 of animal life, it is intended to begin these inquiries with man, and 

 FlG 303 gradually descend in the scale of 



being. 



810. The mucous membrane 

 of the gums, which lies at the bases 

 of the teeth, is peculiar, and re- 

 quires description. 



If a well injected preparation 

 be made, the mucous membrane 

 of the gum will be found covered 



Mac membrane of the gum, tan.n. with papillae. These (in the adult) 



are somewhat long, and consist of 



a single looped capillary, which, through the tension of the injection, 

 becomes more or less twisted (Fig. 303). Their number is very con- 

 siderable, presenting, literally, a forest of them. The papillae of the 

 lips present a gorgeous sight, when well injected ; the loops, as in 

 the former case, twisting with the pressure of the injection. 



THE TEETH. 



811. These *gans, together with the bones, to which they are 

 closely allied, form the sclerogenous (hard) tissues of animals. 



812. Human teeth, and the teeth of the higher mammalia, con- 



