118 



VETERINARY PHYSIOLOGY 



7i.f. 



swelling or ampulla anteriorly. The other two lie in vertical 

 planes each placed diagonally to the mesial plane of the body as 



indicated in fig. 54. The superior 

 of these has a swelling or ampulla 

 in front; the posterior has an 

 ampulla behind. 



The horizontal canals may be 



considered as forming the arc of a 



circle with an ampulla at each 



Fig. 54.— The Relationship of end. The superior canal of one 



the Semicircular Canals to side has its ampulla in front, while 



p.c 



one another, /i.e., horizontal 

 canal ; s.c, superior canal ; 

 p.c, posterior canal. 



of 



a 



circle 



its twin — the posterior of the 

 opposite side — has its ampulla 

 behind, and they together form 

 with an ampulla at each end 



the arc 



(fig. 54). _ 



The bony labyrinth contains a clear lymph-like fluid, and 

 in this a membranous labyrinth lies. 

 (a) In the vestibule are two small vesicles, 

 the saccule and utricle, connected by a 

 narrow duct. 



(6) From the latter of these the 

 membranous seinicircular canals run 

 into the bony canals. Each of them 

 has an ampulla which almost com- 

 pletely fills the bony ampulla in 

 which it lies, while the part lying 

 in the bonv canal is very narrow 



a small part 



only 



Fig. 55. — Bonj" and 

 membranous canal 

 and ampulla to 

 illustrate their 

 mode of action. 



of the lumen 



and occupies 

 (fig. 55). 



On the convex aspect of each ampulla is a 

 thickened ridge covered with columnar cells with stiff 

 hair-like processes, and among these cells the dendritic 

 terminations of the vestibular nerves run. Similar 

 patches exist on the inner aspects of the utricle 

 and of the saccule. A somewhat viscous endolymph 

 fills the membranous labyrinth, and in it over these 

 swellings lie small concretions of carbonate of lime — 

 the otoliths. 



