120 ELEMENTARY BIOLOGY. [CHAP. 



whole to a watch-glass or small vessel filled with 

 water (preferably one having a white bottom). The 

 membranous labyrinth will probably float out ; if 

 not, it may be liberated with a camel's hair brush. 

 It consists of a greyish pigmented structure of the 

 size of a small pea : Note 



u. The vestibule; sac-like and constricted into 

 two — an upper portion or utriculus, and a lower 

 one or sacculus. It is largely filled during life 

 by a milk-white otolithic mass. 



/?. The semicircular canals ; three in number and 

 connected with the utriculus. The anterior 

 and posterior vertical canals, the two divergent 

 ones referred to at b; their inner ends unite 

 before entering the utriculus. The horizontal 

 canal ; situated externally, on a level with the 

 bases of the other two. 



y. The ampulla ; enlargements of the bases of the 

 canals. Those of the anterior and horizontal 

 canals are situated close together at the anterior 

 end of the utriculus. 



8. The ultimate ramifications of the auditory nerve ; 

 visible on the inner face of the labyrinth. 



d. General dissection of the whole auditory organ. 

 Obtain the head of a frog which has been pre- 

 served in spirit, and dissect from behind. 



Scrape the occipital region of the skull quite 

 clean and then pin the whole down under water. 

 Carefully remove the wall of the auditory capsule 

 — externally, to the level of the columella auris — 

 internally, to that of the auditory nerve ; cut away 



