XXXIII.] EAR NOSE. 3/1 



the same period. Fix it finally in osmic acid, embed and cut it in soft paraffin. 

 The retina of this animal is particularly serviceable, because its structural 

 elements are so large. 



26. Lachrymal gland is treated precisely in the same way as the serous 

 salivary glands (Lesson XXIII. ). 



LESSON XXXIIL 

 EAR NOSE. 



EAR. 



1. Membrana Tympani (H). Fix it in osmic acid and mount 

 in Farrant's solution. Observe the radiate yellow-looking fibres, 

 and also fibres disposed circularly, the latter best developed near 

 the periphery of the membrane. The thin epithelial coverings on 

 the two surfaces of the membrane can be seen, and so can a few 

 fine blood-vessels. 



2. Ceruminous Glands of the Meatus. Harden in absolute 

 alcohol a portion of skin from the external auditory meatus, pre- 

 ferably from a new-born infant. Make rather thick sections, stain 

 in haematoxylin and mount in balsam. Observe the Ceruminous 

 glands, which in some respects are like the sweat-glands. They 

 have a narrow duct and a coil, the latter lined by a single layer of 

 cubical cells, and the former by several layers of cells, as in a sweat- 

 gland. In the secretory part smooth muscular fibres lie between 

 the epithelium and the basement membrane. The lumen of the 

 secretory part is very wide, and the lining cells have a clear cuti- 

 cular disc, and contain a yellowish pigment and fatty granules. 



THE COCHLEA. 



Methods. (i.) In a freshly-killed rabbit or guinea-pig, inject, 

 by means of a hypodermic syringe, osmic acid (i p. c.) through the 

 membrana tympani into the middle ear. Cut away the lower jaw, 

 so as to expose the large spherical osseous bulla. Open the bulla, 

 cut away its walls, and expose the middle ear. On the inner wall 

 of the latter are seen the turns of the cochlea. Cut away the 

 surrounding parts from the osseous cochlea, and place the latter in 

 Miiller's fluid (a week), after opening one of the turns, to allow the 

 hardening fluid to penetrate. It is better to do this under fluid, to 

 prevent air entering, as the perilymph escapes. Decalcify in chromic 



