EAR 



187 



and complicated form (Fig. 59). It is made up, in the 

 first place, of two somewhat ovoid sacs separated by a 

 constriction :'the dorsal one is called the utriculus {u), the 

 ventral the sacculus (j), and from the latter a small process, 

 the cochlea (/), projects backwards, and a narrow canal, the 

 endolymphatic duct {d. c), upwards. With the utriculus are 



aa 



rec 



Fig. 59. — External view of left organ of hearing of a Vertebrate (semi-diagrammatic). 

 na, ampulla of anterior canal, ae. of external canal, and ap. of posterior canal ; 

 ass. apex of utriculus ; ca. anterior semicircular canal ; ce. horizontal canal ; cp. 

 posterior canal ; cus. constriction between sacculus and utriculus ; de, se. endo- 

 lymphatic duct ; /. cochlea ; rec, sp, ss, u, utriculus ; s. sacculus. (From 

 Wiedersheim's Vertebrata.) 



connected three tubes, called, from their form, the semi- 

 circular canals, each of which opens into the utriculus at 

 either end. One of them, the anterior canal (ca), is 

 directed forwards ; another, the posterior canal (cp), back- 

 wards ; both these are vertical in position and are united 

 to one another at their adjacent ends, The third, the 



