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' r \ 

 NIVERSITY 



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THE EAR. 



THIS is the only organ of which one cannot give the student a section to carry away 

 with him, on account of their difficulty of preparation, and also because a properly prepared 

 cochlea yields but very few good sections. 



THE SEMICIRCULAR CANALS. 



These are best obtained from the skate, whose cartilaginous cranium should be cut away 

 until the canals with their saccule and utricle are exposed. The canals are hardened in 

 chromic acid and spirit mixture for a week, and then transferred to spirit. The ampullae re- 

 ceive nerves and maybe hardened in osmic acid. Sections "of these canals must be made 

 with a freezing microtome after steeping in syrup and gum. 



THE COCHLEA. 



PREPARATION (A). The guinea-pig is the best animal to employ. Kill the animal and 

 disarticulate the lower jaw, when the osseous tympanic bulla is exposed. It lies just behind 

 the fossa for the condyle of the lower jaw. Cut away the external auditory meatus, and re- 

 move the petrous portion of the temporal bone with the bulla from the other bones of the 

 skull. Open the bulla with bone-forceps, when a conical elevation the cochlea is seen. 

 Remove all the surrounding bone, so as to isolate the cochlea. Place it at once in Muller's fluid, 

 to harden its delicate tissues, for a fortnight. It is necessary, however, to remove the lime- 

 salts from the bone, which is done by transferring the organ to a mixture of chromic acid and 

 nitric acid (p. xxxiii), or to a solution of picric acid. The fluid ought to be shaken from time to 

 time, which greatly facilitates the process of softening. After softening preserve it, first in 

 weak spirit, and then transfer it to strong spirit. When sections are to be made it must be 

 steeped in water, to get rid of the spirit, and then it is subjected to the syrup-and-gum process. 

 These substances support its delicate tissues, and sections must be made parallel with the 

 modiolus, i.e., across the turns of the cochlea, in a freezing microtome. They must be manipu- 

 lated with the greatest care, and ought to be stained with logwood or picrocarmine and 

 mounted in glycerine. 



(B). If the human cochlea be employed, it should be obtained as fresh as possible. Cut 

 out the part of the temporal bone containing the cochlea, from the human subject. Split 

 this up in the axis of the meatus auditorius internus ; this gives two pieces of bone, one 

 containing the cochlea and a part of the vestibule, and the other the semicircular canals 



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