THE SENSE OF MOVEMENT. DYNAMIC SENSE 785 



supplied with a type of sense-organ, the exclusive function of which 

 appears to be to give information regarding the position of our Umbs 

 and body as a whole. The one contained in muscle-tissue, is formed 

 by one or more muscle fibers which are permeated by lyjnph-spaces 

 and are enveloped in a sheath which is made up of several layers of 

 fibrous tissue. The nerve fiber entering this structure, winds spirally 

 around these fibers and eventually terminates in small platelets upon 

 their surfaces. In tendinous tissue this sense-organ appears as an 

 arborization of delicate nerve-filaments upon the surfaces of the in- 

 dividual strands of tissue. This arrangement enables the fibers of 

 the muscle to exert a certain pressure upon these nerve-endings, and to 

 produce impulses which experience has taught us to interpret in terms 

 of a definite degree of contraction of the muscle or of the position 

 of the part moved by it. This central association which, as we have 

 seen, is effected by the cerebellum, constitutes the muscle-sense. 

 These sensations, however, do not amplify merely the sense of position, 

 but also that of motion, because the muscles undergo constant changes. 



CHAPTER LXVI 

 THE SENSE OF MOVEMENT— DYNAMIC SENSE 



The Semicircular Canals. — The membranous semicircular canal 

 occupies from one-third to one-fifth of the entire lumen of the osseous 

 canal. The space intervening between its outer wall and the inner 

 surface of the bony canal, is filled with perilymph and the suspensory 

 bands which hold the membranous tube in place (Fig. 388). In cross- 

 section the latter presents an oval or elliptical outline, and is expanded 

 into a cavernous space very shortly after it leaves the utricle. At this 

 particular point it possesses a diameter about twice as long as that 

 of its remaining portion. This enlargement which is known as the 

 ampulla^ occupies vepy nearly the entire lumen of the osseous canal 

 and lies m close contact with the wall of the latter at the convexity 

 of the semicircle. It gives lodgment to the sensory epithelium mediat- 

 ing dynamic sensations. The latter are conveyed fom here to the 

 center by the vestibular branch of the auditory nerve. ^ 



In cross-section each ampulla presents a transverse prominence 

 which is known as the crista acustica. This ridge projects far into the 

 lumen of this passage and is beset with the sensory epithelium. The 

 latter differs from the flat lining of the remaining portion of the semi- 

 circular canal in that it consists of elongated columnar cells which are 



^ Ewald, Physiol. Untersuchungen iiber das Endorgan des Nerv. Octavus, 

 Wiesbaden, 1892. 



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