112 PHYSIOLOGY CHAP. 



amphibia it is much more developed, and in reptiles it develops 



3V. 



FlO. 45. Membranous labyrinth of l.'t't -i.l.- >i-cn from \vittiout. (McrkH.) <'., cochlea; !>.<., 

 cluctus coehlrai is ; Sue., sacculi- ; ('//., ntricli'; g., superior; <<., external (m lateial): p., 

 posterior semicircular canal ; ".'., aqueduct nt' vi-~til.nl. ; C.r., ranalis 



Fio. 46. Diagram of entire human amlituiy nr^an. (Deliicrrc.) 1, auricular lobe; 2, external 

 auditory meatus ; a, tympanif membrane; 4, stapes attached to base of fenestra vestibuli ; 

 5, bony part of Eustachian tube; 6, its cartilaginous parts; 6', mouth of tube; 7, vestibular 

 cavity filled with perilymph; S, semicircular canals and utricle; ft, promontory; 10, feiipstia 

 cochleae (the arrow indicates tin- tympanic opening of the cochlea) ; 11, tympanic cavity tilled 

 with air ; 12, cochlear duct filled with endolymph, united to saccule of vestibule by a narrow 

 junction canal ; 13, scala vestibuli ; 14, scala tympani terminating in fenestra cochleae ; 

 15, apex of cochlear canal, where the two walls unite at 15' ; 115, cochlear aqueduct ; 17, vesti- 

 bular aqueduct ; IS, endolymphatic sac ; 19, parotid region. 



progressively from the chelonians and ophidians to the saurians 

 and crocodiles. It is only in these last and in birds that the 



