CHAPTER l 



THE CEREBELL1 M AND THE SEM* [R( i l..\i; CANALS 



FUNCTIONAL TESTS 



The cerebellum serves as the great aerve center to which are transmit- 

 ted, through the various proprioceptors, the impulses which, as it w< 



inform it as to the exacl degri t muscular effort required to maintain 



the animal in its various postures, h is, as Sherrington ; 

 ganglion of the proprioceptive system. Such impulses from the na 

 tendons, etc., could not, however, supply information regarding the 

 position of the body in space. For this purpt I receptors eon- 



nected with the eighth nerve are provided in the semicircular 

 These, it will be remembered, are three in number on either side, each canal 

 consisting of a semicircular bone tube attached to the vestibu 

 interna] cat-: and they are arranged so thai they lie at right ang one 



another in the three planes of space. The thr< anals on eithei 



thus disposed so as to form an arrangemenl like a V-shaped armchair with 

 the back inwards. This arrangement causes the posterior vertical canal 

 of one side to be in the same plane as the superior vertical canal of I 

 opposite side, the external canals being in the horizontal plane on hoth 

 sides. The arangement will be plain from the diagram Fig. 227 . 



Within the osseous canals are suspended membranous tubes, which do i 

 fill the canals. The canals, etc., contain fluid, but are not completely 

 filled. The osseous as well as the membranous canals are dilated at 

 end to form the ampulla, and it is here that the vestibular division 

 eighth nerve ends in a structure called the "crista acustica," 

 hair ••ells supported by sustentacula cells. The q< irminates in fine 



arborizations between the hair cells, [nt ad utricle an j1 



t hits similar to the crista, called the macule acust l - st 



r ptors specialized for the purpose of respond ii I in the 



position of the head, and therefore of the body in general. When the 

 head moves in a certain plane of Bpace, the fluid in the membran 



and in the utricle and saccule "ii a unit of inertia nn-i 



movement, which acts on the hi lis and I 



stimulus. According to the d< timulation in tl 



ampulhe. which again will be ^i'} I upon tl 



which the movement of the head I urred, impuls 



