THE FROG. 121 



the hinder half of the tympanic membrane, to the 

 level of the head of the columella. 



Work over the mutual relations of the following, 

 all of which have been previously described. 



a. The columella auris; to the tympanic membrane 

 and fenestra ovalis. 



/?. The membranous labyrinth ; to the periotic cap- 

 sule and its enclosed cavity. 



y. The auditory nerve; to the membranous laby- 

 rinth and brain. 



8. The Eustachian recess; to the mouth cavity, 

 and that of its lining membrane to the colu- 

 mella. 



e. The annulus tympanicus ; to the membrana 

 tympani. 



Histology. 



In the undermentioned directions, the reagents which 

 may preferably be employed in each case are alone 

 enumerated; details as to preparation and methods 

 of treatment will be found in the Appendix. 



The blood. 



a. Freshly drawn blood. Obtain a drop of the same 

 from a freshly-killed frog, and examine with a 

 low power, under a cover-glass, 

 a. The plasma ; thin, watery and colourless. 

 /3. The corpuscles; exceedingly numerous solid 

 bodies, freely suspended in a. Two kinds will 

 be seen: larger and more numerous red cor- 

 puscles; smaller and less numerous white cor- 

 puscles, irregular in shape, greyish in colour, and 



