THE EAR. 275 



CHAPTER XXI. 



THE EAR. 



THE only parts of the ear which require special 

 directions for their preparation are the semicircular 

 canals and the cochlea. 



Preparations 1, 2, and 3. The semicircular 

 canals. To study the structure of the membranous 

 semicircular canals, those of the cartilaginous fishes, 

 e.g. the skate, are chosen. The skull, which can he 

 readily cut with a scalpel or strong pair of scissors, 

 is opened quite anteriorly, where it is occupied 

 merely by a quantity of cerebro-spinal fluid, and 

 the opening is extended backwards by removing 

 the roof bit by bit, until the whole of the upper 

 surface of the brain is exposed. Two thick carti- 

 laginous masses will be seen, one on either side, near 

 the posterior part ; the large auditory nerves pass 

 through a foramen in each into their interior. 

 These masses inclose the membranous labyrinth, 

 consisting in these animals of utricle, 'saccule, and 

 semicircular canals, all of large size, and contained 

 in corresponding cavities and canals, in the sub- 

 stance of the cartilage, but of which no trace can 

 at present be made out. If, however, horizontal 

 slices are made with a scalpel, one of the canals will 

 soon be exposed, and this can then be followed in 

 both directions, cutting the cartilage away so as to 

 expose the included membranous canal in its whole 

 length. It will be found to lead at either end into 

 a large membranous bag the utricle with which 

 the two other canals also communicate, and from 

 which they can be traced in the same manner. 

 Besides the utricle, there is another smaller mem- 



