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A TEXTBOOK OF PHYSIOLOGY 



angle of about 37 degrees to the coronal plane, and the posterior canal 

 at an angle of about 37 degrees to the sagittal plane. The superior 

 canal of one side forms, therefore, an angle of 15 degrees with the 

 posterior canal of the opposite side. There is a considerable space 

 between the bony and the membranous canals. The former are 

 filled with perilymph, the latter with endolymph. 



The special receptor mechanisms lie within the utricle and the 

 ampullae of the semicircular canals. The specialized structures of 

 the ampullae are known as the cristae. They consist of specialized 

 nerve-epithelial hair cells and supporting cells, which lie upon a base- 

 ment membrane, supported upon a hillock of subeiidothelial tissue, 

 through which pass the nerve-endings of the vestibular part of the 

 eighth nerve, to arborize around the hair cells. 



In the utricle and saccule there are somewhat similar structures, 

 known as the maculae (Fig. 383). These have, in addition, crystals 

 of calcium carbonate (otoliths), which lie among the hair cells. 



FIG. 383. PORTION OF THE MACULA OF A MOUSE, TREATED BY GOLGI'S METHOD TO 

 SHOW NERYE-EXDIXGS IN THE SENSORY CELLS (sen.c.). (Redrawn after V. 

 Lenhossek from Dahlgren and Kepner.) 



b.m., Basement membrane; sup.nu., nuclei of supporting cells; nv.f., nerve-fibre. 



The vestibular ganglion, or ganglion of Scarpa, lies in the internal 

 auditory meatus, an upper nerve-branch connecting with the utricle 

 and the ampullae of the superior and external canals, a lower nerve- 

 branch with the saccule and the ampullae of the posterior canals. 

 Centrally the fibres enter the medulla oblongata in the region of the 

 restiform body, and make connections as described later (see p. 699). 



The first proof that the semicircular canals are concerned with 

 equilibration was adduced by Flourens in 1828. He showed that 

 injury of one canal produced rotatory movements of the body, the 

 axis of rotation being at right angles to the severed canal. He noticed 

 that the disturbances, like those produced by injury of the cerebellum, 

 were of a co-ordinated nature, due to one set of muscles contracting 

 while another set relaxed. For many years Flourens' work passed 

 unnoticed, but since then it has been many times confirmed. 



The extirpation of both labyrinths is attended with most marked 

 vipset of equilibration. 



