HIGH SCHOOL ZOOLOGY. 



37 



Fig. 15.— Right Ear of Catfish, from « ithin. XI. 



A.SC, hsc. ]isc, anterior, horizontal and posterior senii-oircular canals ; aa, ha, pa, 

 their anipulhc ; nt, utrieulus ; ru, recessus utriculi ; VMI, anterior and posterior 

 In-anchcsof auditory nerve ; co, laifena cochlea; ; s, sacculus ; tr, opening of transverse 

 duct communicating with the left ear. 



46. Of the two parts into which the labyiinth i.s divided, 

 (Fig. i5) the lower is largely concealed by a little shelf project- 

 ing from each ex-occipital bone, and meeting in the middle line 

 over the basi-occipital. This part is known as the saccule and 

 lagena coclilese, each of which is a delicate membranous sac, con- 

 taining fluid (th.? endolympli) and an ear-stone or otolitli and 

 receiving a considerable part of the auditory nerve, the fibres of 

 which terminate in certain cells of the lining membrane. The 

 upper part is more easily seen ; it is connected with the lower 

 by a narrow duct, and is formed of a central tube, the 

 utrieulus, with a large membranous sac projecting forwards 

 fi-om it, and containing a very large otolith and corresponding 

 branch of the auditory nerve. Into the uti-iculus and its 

 recess there open the thre? semi-circular canals, anterior 

 posterior and external, which are respectively situated approx- 

 imately in sagittal, frontal and horizontal i>lanes. Their lower 



