THE ELASMOBRANCH FISHES 



271 



Auditory Organ 



Superfieiall.y the ear is protected by the cartilaginous auditory capsule which, 

 in the embryo, joins the parachordal cartilages of the cranium (see p. 53, fig. 

 58). In certain types the capsule is so thin as to give indications of the semi- 



C D 



Fig. 237. Ear of Elasmobranchs. (From Retzius.) 



Squatina : A. Outer view of left ear. B. Inner view of right ear. 



Baja ■• C. Outer view of left ear. D. Inner view of right ear. 



(For explanation see fig. 2.36.) 



circular canals superficially. Two pairs of apertures may enter the capsule 

 from the parietal fossa in the middorsal line. The first and smaller of these is 

 for the endolymphatic ducts (e.d., figs. 59 and 62) , while the second and larger 

 pair of apertures are the fenestrae (fn.). These apertures may be considered 

 more in detail. 



I have previously mentioned fenestrae for a number of sharks and for some 

 of the rays (p. 55) . If we refer to figures of the dorsal view of the skull (figs. 

 59 and 62) we observe that these openings are well marked and take up their 



