THE SENSE ORGANS 



421 



Proof of the static function of utriculus, sacculus, and semicircular 

 canals has been obtained by extirpation experiments upon lower animals. 

 An animal without these parts of the ear is unable to orient its body in 

 space. The action of the endolymph upon the hairs of the cristae and 

 maculae is intensified by the presence of small calcareous crystals or 

 otoconia in the endolymph. 



The Organ of Hearing. The organ of hearing is the cochlear duct, 

 otherwise known as the scala media, which is attached to the outer side 

 of the spiral bony cochlea. The cochlear duct is connected with the 

 sacculus by means of a narrow tubular ductus reuniens. The sacculus is 



COCHLEAR DUCT 



OUTER 

 /\HAIR CELLS 



l/DE ITERS 

 CELLS 



-GANGLION CELL SCALA TYMPANI 



Fig. 370. — A stereqgram of a portion of the organ of Corti (spiral organ) of man. 

 The precise function of the tectorial membrane is uncertain. It may serve as a damp- 

 ener or it may intensify the action of the "sound waves" upon the sensory hair cells. 

 (Redrawn after Fritz Kahn, " Der Mensch," Albert Miiller, Zurich.) 



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 utriculo-saccular duct by means of the 

 endolymphatic duct. (Fig. 367, 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 

 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, 



