EXPLANATION OF THE PLATES. 



PLATE VII. 



Obs. It is scarcely necessary to observe, that the com- 

 parative anatomy figures are introduced in this work for the 

 purpose of illustrating in a more satisfactory manner than 

 could be otherwise accomplished, certain points, especially the 

 more obscure ones, connected with human anatomy. 



These figures should, therefore, by no means be regarded 

 as taking the place of any of those which should illustrate 

 human anatomy, and not one of which, deemed to be of im- 

 portance, will on any account be omitted ; they should be 

 deemed not as substitutes, but as additions to the original 

 design of the work, and which cannot but enhance very con- 

 siderably its value. 



Fig. 1. Represents a portion of the under surface of the 

 tongue of the frog, magnified 130 diameters, and on 

 which are seen, first, numerous glands, mostly 

 spherical, and traversed by a tortuous vessel in 

 which the blood corpuscles are tossed about as it 

 were in a vortex; and, second, mucus crypts, the 

 apertures of which are apparent. Donne has ob- 

 served these bodies, but believes them to be formed 

 by nervous loops, and appears to have overlooked 

 the orifices alluded to : these I found to be figured 

 in a drawing of the tongue of the frog, sent me by 

 Dr. Waller, but unaccompanied by any explana- 

 tion. 



Fig. 2. A portion of the same, magnified 500 diameters, 

 shewing the incurrent and excurrent vessel of the 

 gland, the mucus crypts, and the net-work formed 

 by the epithelium. 



