Mechano- and Equilibrium-Reception 



517 



cochlea, functions in hearing; (2) the upper portion, consisting of the 

 utriculus and the semicircular canals, functions in orientation. The utric- 

 ulus conforms reasonably closely to the basic plan of a statocyst, (page 

 514). The semicircular canals are bent tubes, both ends of which com- 

 municate with the utriculus. The bent tubes bear an enlargement at one 

 end, the ampulla, in which is located the sense organ (Fig. 186), consisting 

 of the crista and the gelatinous cupula, which approximately fills the cavity 

 of the ampulla (p. 475, Ch. 13). 



Fibers in the vestibular branch of the eighth nerve are of three types: 

 those activated onlv bv mechanical vibration of low frequency; those acti- 

 vated by tilting movements only; and those activated by angular accelera 

 tion.^- McNally and Tait'^^ rendered the utriculus of frogs non-functional 

 by cautery without encroaching on the semicircular canals and determined 

 that the response to tilting and linear acceleration was abolished. It is gen- 



Fig. 186. Diagrammatic sketch of the cupula and crista after Kolmer. A, hair 

 cells whose terminal processes protrude into F, the gelatinous cupula; B, support- 

 ing cells; D, large nerve fibers; E, small nerve fibers. From Fulton."'" 



erally accepted that the utriculus responds to these movements. The 

 function of the sacculus is less clearly established. In the frog, section of 

 the ner\'es from the saccular maculae does not produce any disturbance 

 of orientation. '' Von Buddenbrock^^ states that the sacculus does not function 

 in orientation except in rabbits, in which vertical eye movements are elicited 

 by stimulation of the sacculus. The consensus at present""' -^^ is that 

 the sacculus responds to mechanical vibrations of low frequency. Con- 

 cerning the function of the semicircular canals, there exists a vast litera 

 j-yjg 40. 14, 70 j]^p work of Lowenstein and Sand,"- Steinhausen,"" and 

 Dohlman-- serves to clarify the function of the semicircular canals. 



Lowenstein and Sand*'- recorded nerve impulses from single nerve fibers 

 from an excised horizontal semicircular canal of the skate. Raja clavata. In 

 all preparations the\' obserxed a spontaneous discharge of impulses under 

 stationary conditions. The frequency of this background discharge varied. 

 Rotation of the preparation toward the side of the canal (ipsilateral rotation) 



