280 THE ESSENTIALS OF HISTOLOGY. 



LESSON XLV. 



STRUCTURE OF THE LABYRINTH. 



1. SECTIONS across one of the membranous semicircular canals of a fish 

 (skate). 



2. Longitudinal sections through the ampulla of a semicircular canal 

 (skate). 



1 and 2 may be hardened in chromic and osmic acid (see below under 3) 

 and embedded in celloidin. 



3. Vertical sections through the middle of the cochlea of a mammal 

 (guinea-pig). 



The cochlea is put quite fresh into O2 per cent, chromic acid containing a 

 few drops of 1 per cent, osmic acid, or into Flemming's solution (see Appendix). 

 When decalcified, it is well washed, and then placed in spirit for a day or 

 more. 



In preparing sections of the above three preparations it is advisable, in 

 order that the epithelium should be kept in position, to embed in celloidin 

 or, if the paraffin method of embedding be preferred, to fix them to the slide 

 by an adhesive process. They should previously be stained in bulk. 



4. Teased preparations of the auditory epithelium of an ampulla or of the 

 macula of the utricle, from the fish. 



5. Teased preparations of the epithelium of the organ of Corti from the 

 guinea-pig. 



Both 4 and 5 are made from osmic preparations. 



Make sketches from all these preparations under the high power. 1 



The labyrinth, which is the essential part of the auditory organ, 

 consists of a complex membranous tube lined by epithelium and filled 

 with endolymph, contained within a bony tube the osseous labyrinth 

 of corresponding complexity of shape (figs. 312, 313). The mem- 

 branous labyrinth does not wholly fill the bony cavity ; the rest of the 

 space is occupied by perilymph. The membranous labyrinth (fig. 312) 

 is composed of the utricle (u), and the three semicircular canals, each 

 with an enlargement or ampulla which opens into it, the saccule (s) 

 and the canal of the cochlea (c.c.). 



The ^tranches of the auditory nerve pass to certain parts only of the 

 membranous labyrinth, viz. the maculae of the utricle and saccule ; 



*For the methods of obtaining the various parts of the labyrinth for microscopical 

 examination, the reader is referred to the author's Course of Practical Histology. 



