Metazoa Rana. 



321 



capsule of the frog contains a cavity, lined by a mem- 

 branous capsule, which fits it exactly. The membranous 

 capsule, which takes the form of a partially divided vestibule 

 with semicircular canals opening into it, is composed of a 

 framework of connective tissue carrying modified ciliated 

 epithelial cells. These cells are connected with the termina- 



FIG. 177. THE MEMBRANOUS LINING 

 OF THE RIGHT INTERNAL EAR OF 

 THE FROG FROM THE OUTER ASPECT. 

 (Millies Marshall.) 



a, anterior vertical semicircular canal ; 

 b, ampulla or swelling on it ; h, hori- 

 zontal canal and its ampulla, i ; p^ 

 posterior vertical canal and its am- 

 pulla, r '\ s, sacculus and 7/, utriculus, 

 the two subdivisions of the vestibule. 



FIG. 178. SENSORY EPITHELIUM 

 OF THE EAR. (Quain.) 



c, c, sensory cells ; f, f, support- 

 ing cells ; , nerve ; h, /t', cilia. 



tions of the auditory nerve. The cavity of the capsule is 

 filled with lyrnph into which the cilia of the cells project. 

 The wall of the cavity is perforated at one point, termed the 

 fenestra ovalis, which, however, is closed by a delicate 

 membrane, to which is fastened on its outer side a small 

 rod-like bone, known as the columella, whose outer end 

 abuts against the membrana tympani already described as 

 visible on either side of the skull behind the eyes. The 

 intermediate chamber (or tympanic cavity) containing the 

 columella communicates with the buccal cavity by a tube, 

 known as the Eustachian tube, whose opening has already 



