VIII THE MEMBRANOUS LABYRINTH 391 



fall. The particular sensation from the legs, which in a 

 normal i)erson helj) in co-ordination, are to some slight 

 extent those from the skin of the feet, but more especially 

 are those from the joints and the muscles. These sen- 

 sations from the limbs are thus the second class of 

 sensation which contribute to tlie power of coordination. 



But even more important than either the sensations from 

 the eyes or from the limbs are a third set which come 

 from a special organ which exists for the purpose of 

 appreciating alterations in the position of the body with 

 regard to the objects around it just as definitely as the 



Fig. 123.— The Membranous Labyrinth, twice the natural size. 



Ut. the (Jtrkie, or part of the vestibular sac, into which the semi- 

 circular canals open ; A. A. A, the ampulla; ; P. A, anterior vertical semi- 

 circular canal ; F. V, posterior vertical semicircular canal ; //, horizontal 

 semicircular canal. The saccule is not seen, as in the position in which 

 the labyrinth is drawn the saccule lies behind the utricle. The white 

 circles on the ampullae of the posterior vertical, and horizontal canals 

 indicate the cut ends of the branches of the auditory nerve ending in 

 those ampullse ; the branch to the ampulla; of the anterior vertical 

 canal is seen in the space embraced by the canal, as is also the branch 

 to the utricle. 



eye sees or the ear hears. This organ is the membranous 

 labyrinth of the ear, the utricle and the semicircular 

 canals. The giddiness which is invoked by turning 

 rapidly and then stopping suddenly gives rise to a 

 definite sensation because this definite organ is stimulated 

 in just the way that it would be if the person and the 

 room were rotating relatively to one another. In order 

 to see that this is so we must understand the structure of 

 the labyrinth of the ear. 



