786 



THE SENSE OF EQUILIBRIUM 



surmounted by long tapering processes. These hair-like extensions 

 measure about 0.03 mm. in length and project straight into the en- 

 dolymph. Somewhat above the basement membrane these cells termi- 

 nate in a rounded extremity which lies in relation with the finely 



N 



FIG. 398. DIAGRAMMATIC REPRESENTATION OF THE STRUCTURE OF THE AMPULLA OF A 



FISH. 



The columnar cells of the crista acustica (c) are beset with hair-like prolongations 

 which float free in the endolymph. N, nerve fibers leading away from ampulla. 



subdivided axis cylinders of the vestibular nerve fibers. The space 

 between the lower poles of these hair-cells and the basement mem- 

 brane is taken up by the fiber cells of Retzius 1 which present themselves 

 as long filaments showing at one point a nuclear enlargement. 



The Relative Position of the Semi- 

 circ.ular Canals. 2 The three osseous 

 semicircular canals take their origin 

 from the vestibular enlargement of the 

 labyrinth, while the three membranous 

 canals arise from the utricle. Since two 

 of these tubes, namely, the two vertical 

 ones, become confluent before they 

 again return to this space, they possess 

 only five orifices in all. The three 

 canals of each side are arranged in such 

 a way that they cover three distinct 

 planes which lie approximately at right 

 angles to one another. The external 

 or horizontal canal measures 15 mm. in 

 length and traverses a plane at right 

 angles to the mesial plane of the body 



FIG. 399. FIGURE SHOWING THE (Fig. 399EO- It occupies, therefore, a 

 POSITION OF THE THREE SEMICIRCULAR horizontal position when the head is held 



" SKULL F ^ PlGE N ' erect " Its ampulla is located anteriorly. 

 The anterior or superior canal is placed 

 nearly vertical at an angle of 45 to the mesial plane of the body (A). 



1 Biolog. Untersuchungen, vi; also: Brener, Sitzungsber., Akad. zu Wien, 

 cxii, 1903. 



2 First called attention to by Cyon (1873), Brown (1874), and Mach (1875). 



