THE ORGANS OF SENSE. 



SECTION Y. 

 PROPRIOCEPTIVE SENSES. 



Our knowledge of the position of the body is derived partly from 

 tactile and visual impulses, and partly from impulses reaching the 

 central nervous system from the posterior part of the labyrinth and 

 from the skeletal muscles ; the impulses arising in the muscles and 

 labyrinth are called proprioceptive impulses. 



The Labyrinth. The part of the bony labyrinth behind the cochlea 

 consists of a cavity called the vestibule, into which the scala vestibuli 

 opens in front and three semicircular canals open behind. Within the 



FIG. 48. The membranous labyrinth. (Enlarged.) Gray's Anatomy. 



bony semicircular canals lie the three membranous semicircular canals 

 (ducts). The latter open into the membranous utricle, which, along with 

 the saccule, occupies the vestibule, the utricle and saccule being connected 

 by the saccus (ductus) endolymphaticus (fig. 48). The semicircular 

 canals are arranged in three planes at right angles to one another. 

 The external canal lies in the horizontal plane ; the superior vertical 

 canal and the posterior vertical canal lie in vertical planes at right 

 angles to one another, as shown in fig. 49. 



The canals open into the utricle by five orifices, one of which is 

 common to the medial end of the superior and the upper end of the 

 posterior canal ; each canal has a dilatation or ampulla at one end. 



The utricle, saccule, and semicircular canals are lined by flattened 

 epithelium resting on connective tissue ; in each ampulla the connective 



