No. I.] 



THE VERTEBRATE EAR. 



As a basis for the account of the vertebrate ear which 

 follows, I shall describe the Elasmobranch ear, using for this 

 purpose, one Selachoid and two Ba- 

 toid forms, — Carcharias littoralis, 

 Dasyatis centrums, and Torpedo occi- 

 dentalis (PL I, Figs, i, 2, and 3, and 

 Cut i). In Fig. I is shown the left 

 ear of Dasyatis, seen from the out- 

 side. The most important feature 

 of this ear is the perfection in which 

 the canal plan, or the arrangement 

 of the canals, is presented. The 

 primary channel of communication 

 with the surface parent canal, the 

 ductus endolymphaticus {de.), enlarges 

 gradually as it sinks into the head. 

 Its enlarged lower end is bifurcate, 

 the median raphe of the utriculo-sac- 

 culus separating the primary cham- 



, . ^ , 1 ^1 Cut I. — The left internal 



ber into two secondary — -the per- r ^ ^ , -7 . ;• j- 



■^ ^ ear of Torpedo occidentahs dis- 



manent or adult ones, which are the sected out of its cartilaginous 



Utriculus ill) and the sacculus {s) capsule, and viewed from the out- 



of anatomists. From the utricular '^^^- ^"^^ somewhat diagram- 



T , ... . , , matic figure represents the ear 



chamber near its iunction with the , . . ■ •. . , • 



J about twice its natural size, as 



endolymphatic duct is given off a found in a fish five feet in length. 

 tube, short and relatively narrow, -4«, anterior ampulla; a*', anterior 



which soon enlarges into the anterior ^^^^^^^ ^^' ^^^^^^"-^^ "^-^^^^ c.e, en- 



. dolymphatic canal; co, utriculo- 



canal complex (,r) ; similarly, from the ^^^^^^^^ ^^^^. ^.^ ^^^^^^^^ ^^. 



sacculus, but further down on its pulla; Ht, external canal; mu, 

 body, is given off a tube which opens macula utriculi, auct.; /, lagena 



into the posterior canal (z). This ^"^ P"?^"^ ^"-'"^' ^' ^""'^^^^ 



pore of endolymph canal ; s, its 



ear, then, shows very plainly the two g^^. p^^ posterior ampulla; P^, 



chambers usually described as SUpe- posterior canal; ^'C, sacculus and 



rior and inferior divisions of the ear its macula sacculi; f/' and £/", 



utriculus and utriculo - saccular 

 chamber. 



cavity, or the utriculus and sacculus, 



and it is perfectly evident that these 



chambers are not superposed, but placed one beside the other 



in an antero-posterior direction. 



The utricular and saccular chambers are nearly equal in 

 size in Dasyatis ; but in most other Elasmobranch forms, as 



