THE SENSE ORGANS 



60 1 



also connected with a slender endolymphatic duct, which terminates in a 

 swollen saccus endolymphaticus near the dura. The utriculus connects 

 with the sacculus through the utriculosaccular duct by means of the 

 endolymphatic duct. (Fig. 494, G) 



Throughout the two and a half turns of its extent, the membranous 

 duct of the cochlea is triangular in cross section, and is attached at its 



SCALA VESTIBUU 



SOUND WAVES IN 

 PER I LYMPH 



PILLAR CELLS 



SCALA TYMPAN 



COCHLEAR DUCT 



COCHLEAR NERVE \^^^^^ ^^ ^^^^, 



Fig. 498. — A stereogram of a portion of the cochlear duct of man. The figure 

 suggests how "sound waves" are conveyed to the hair cells of the organ of Corti. 

 (Redrawn after Kahn's "Das Leben Des Menschen," W. Keller & Co.) 



apex and base to the surrounding bone. The side lying towards the 

 greater curvature of the cochlea consists of a much thickened periosteum, 

 the spiral ligament. The upper side, the vestibular membrane, consists 

 of a thin sheet of connective tissue, covered on both sides by flattened 

 epithelium. As in reptiles, the apex of the triangle is fastened to the thin 

 bony lamina which projects into the perilymphatic cavity, and partly 

 divides this into a dorsal cavity, the scala vestibuli, and a ventral cavity, 

 the scala t5mipani, both of which are filled with perilymph and connected 

 with one another at the apex of the cochlea. (Fig. 498) 



The third and lower side of the cochlear duct is the essential auditory 

 organ, the spiral organ of Corti, which rests upon a connective tissue 



