AMPHIBIA. 



219 



The middle ear consists of a small tympanic cavity, communicating 

 by the short Eustachian tube with the back of the mouth-cavity, and 

 lined by a continuation of its epithelium. It is closed externally by 

 the rounded tympanic membrane, which is stretched over a cartila- 

 ginous ring connected with the squamosal and covered externally 

 by skin. The rod-like columella (Fig. 50, B) is attached at one 

 end to the tympanic membrane, and stretches across the cavity 

 to the fenestra ovalis, into which its other end is inserted. 



The internal ear is made up of the membranous labyrinth (Fig. 62), 

 contained in the cavity of the auditory capsule which, however, 

 it does not fill. Numerous strands of connective tissue unite it 

 with the walls of this cavity, which is filled by a clear fluid, the 

 perilymph. The labyrinth is of complicated shape, and consists of 

 vestibule and semicircular 



canals: (1) The vestibule A B 



is divided into (a) the utri- 

 culus, an irregular bag, the 

 cavity of which is imper- 

 fectly bisected by a fold 

 and communicates by a 

 small aperture with that of 

 Q3) the sacculus, an under- 

 lying oval bladder. Three 

 small swellings on the pos- 

 terior side of the sacculus 

 receive collectively the 

 name of cochlea. (2) The 

 semicircular canals are three 

 curved tubes anterior 

 vertical, posterior vertical, 

 and external horizontal, 

 connected with the utri- 

 culus. They lie in planes 

 mutually at right angles. 

 The first and last dilate 

 into swellings (ampullae) in 

 front, where they join the 

 utriculus. The posterior vertical unites in front with the anterior 

 vertical to form a common tube opening into the utriculus, and 

 dilates behind into an ampulla. 



Fig. 62. SENSE ORGANS or FROG (after 

 JS fleer and Wiedersheim), various scales. 

 A, Cells from olfactory epithelium; ol.c 

 olfactory -cell. B, Right Membranous 

 Labyrinth, viewed from outside. The 

 arrow points to the front. The branches 

 of the auditory nerve are shown (partly 

 dotted), ut, Utriculus; sc, sacculus; 

 a.v, p.v, and h, anterior vertical, pos- 

 terior vertical, and horizontal semi- 

 circular canals ; ap, ampullae ; co, coch- 

 lea. B', 1, auditory cells, with auditory 

 hairs, a. h; 2, supporting-cells. 



