6oo 



COMPARATIVE ANATOMY 



by columnar epithelium and loosely attached by connective tissue to the 

 periosteum of the otic bone. Connected at both ends with the utriculus, 

 each canal swells at one end into an ampulla. On one side of each ampulla, 

 an elongated cluster of hair-cells forms a crista, which is innervated by a 

 branch of the vestibular nerve. 



The elongated hairs of the sensory cells of the crista extend into the 

 endolymph, the movements of which are communicated to the hairs, and 

 thus indirectly to the nerves connected with the hair-cells. Similar 

 patches of hair cells, the maculae, with shorter hairs, occur on the sides 

 of the utriculus and sacculus and, like the cristae, have a static function. 



COCHLEAR DUCT 



OUTER 

 /\HA1R CELLS 



^gP^-NERVE FIBERS 

 GANGLION CELL 



|/DE ITERS 

 CELLS 



SCALA TYMPANI 



Fig. 497. — A stereogram 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 Kahn's "Das Leben Des Menschen," W. Keller & Co.) 



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

 canals has been obtained by e.xtirpation experiments upon lower animals. 

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

 space. The centers of equilibration in the brain are closely associated 

 with those of the vagus nerve; so that the sea sickness which follows con- 

 tinuous and violent disturbance of the static organ results from its relation 

 to the nerve which innervates the stomach. 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 



