AUDITORY ORGAN 227 



expanded distally to fit against the tympanic membrane. The 

 colurnella is wanting in certain Urodeles (e.g., Triton). A mem- 

 branous fenestra rotunda in the outer wall of the auditory capsule 

 is present in most Amphibians and in all higher Vertebrates in 

 addition to the fenestra ovalis. 



The ear of the Gymiiophioiia resembles that of the Urodela, but the 

 membranous labyrinth shows further complications. 



FIG. 181. RIGHT MEMBRANOUS LABYRINTH OF Rana esculenta, from the inner 

 side. (After G. Retzius. ) 



<JLU, aperture of utriculus ; I, lagena cochlea? ; pb, pars basilaris cochleae ; CMS, 

 utriculo-saccular canal ; mu, ms, mn, macula acustica recessus utriculi, 

 sacculi, and iieglecta ; pi, ppb, papilla acustica lagense and basilaris ; rua, rap, 

 rs, rn, rl, rb, branches of auditory nerve to the anterior and posterior ampulla?, 

 sacculus, macula neglecta, lagena, and pars basilaris. (Other letters as in 

 Fig. 180, A 1 C.) 



Reptiles and Birds. In Chelonians, the auditory organ 

 shows many points of resemblance to that of Urodeles ; and in all 

 Reptiles and Birds the chief modifications are confined to the 

 lagena or cochlea, which gradually shows a higher condition of 

 development in passing from Chelonians and Snakes to Lizards 

 and Crocodiles. In Chelonians, the cochlea grows out in the form 

 of a short canal ; in Crocodiles arid Birds this canal is considerably 

 longer, and at the same time it becomes slightly coiled (Figs. 182 

 and 183). A more marked differentiation also gradually takes 

 place in the membrana basilaris and the papilla acustica basilaris. 

 Both become more and more elongated ; and, at the same time, 

 distinct indications of scalce tympani and vestibuli are seen. (Com- 

 pare the description of these parts on p. 232.) 



In the Lacertilia the most varied types of auditory organ are met with ; 

 in many (Phrynosoma, Pseudopus, Anguis), the membrana basilaris is hardly 

 more highly developed than in Ophidia. In Iguana, an advance towards 

 Lacerta and the other higher Lizards is to be noticed : the membrana 

 basilaris is longer, though the lagena with its papilla is not so prominent. 

 In Acantias and Platydactylus this state of things is carried still further, and 

 finally the more highly developed auditory ororan of Plestiodon and Egerina 



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