74 



SPECIAL SENSES. 



and bony chain; (1 1), A, the labyrinth, in which the nervous 

 expansion floats; B, the semicircular canals; andC, the cochlea. 

 The labyrinth is the true auditory organ, and is more or less 

 developed wherever audition exists as a special sense. Com- 

 parative anatomy shows many phases of structure in this 

 intricate apparatus. 



[ 151. The labyrinth is situated (fig. 45) /, m, in the most 

 solid portion of the temporal bone : it consists of three portions 

 (fig. 51); the vestibule (a) ; the semicircular canals (b) ; and 

 the cochlea (c). 



Fig. 51. Views of Labyrinth. 



Posterior. 



Anterior. 



Inferior. 



Fig. 52. Vertical Section ; internal 

 surface. 



Posterior. 



Anterior. 



[ 152. The vestibule (Fig. 5 1, a) is placed at the inner side of 



the drum, with which it com- 

 municates by the oval hole (fig. 

 52, 11) ; it is surrounded by 

 the cochlea and semicircular 

 canals. This small chamber is 

 about the size of a grain of 

 wheat; into it open the five am- 

 pullae of the semicircular ca- 

 nals (19, 19, 19, 19, 19) ; 

 the opening for the passage of 

 the auditory nerve (20) ; on 

 the fore and under part is a hole leading to the cochlea (21); 

 Fig. 53.-Semicircular ^behind is the aqueduct of the ves- 

 canals. tlbule ( 22 )- 



[ 153. The semicircular canals (fig. 

 53, b) rise from the superior and pos- 

 terior part of the vestibule, immediately 

 behind the tympanum. They are three 

 in number, in the form of tubes, with 

 flask-like swellings at their extremities. 

 From their position they are named the 

 vertical, or superior (23) ; the oblique, 

 " ""/ ''$ or posterior (24) ; and the horizontal, or 



Anterior View. inferior (25). As two of the canals ter- 



