HEARING. 429 



Fig. 395, which is on a still larger scale than 

 the preceding figure, the osseous labyrinth is 

 laid open, so as to show the parts it encloses, 

 and more especially the membranous labyrinth, 

 floating in the perilymph (p). The form of 

 this latter part is still more distinctly seen, in 

 Fig. 396, where it is represented in a position 

 exactly corresponding to the former figure, but 

 wholly detached from the bony labyrinth, and 

 connected only with the nervous filaments which 

 are proceeding to be distributed to its different 

 parts. 



A simple inspection of these figures, in both 

 of which the corresponding parts are marked by 

 the same letters, will show at once the form and 

 the connexions of the three semicircular canals, 

 (x, Y, z), each of which present, at their origin 

 from the vestibule, a considerable dilatation, 

 termed an ampulla (a, a, a), while, at their other 

 extremities, where they terminate in the vesti- 

 bule, there is no enlargement of their diameter : 

 and it will also be seen that two of these canals 

 (x and v) unite into one before their termination. 

 The same description applies in all respects 

 both to the osseous and to the membranous 

 canals contained within them ; the space (p) 

 which intervenes between the two, being filled 

 with the perilymph. But the form of the 

 membranous vestibule demands more particular 

 notice, as it is not so exact an imitation of that 



