232 THE ESSENTIALS OF HISTOLOGY 



LESSON XLIL 



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). 



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

 The cochlea is put quite fresh into 0*2 per cent, chromic acid containing 



a few drops of 1 per cent, osmic acid. 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 mount them by the 

 creosote-shellac process. They may previously be stained in bulk either by 

 alcoholic magenta or borax-carmine. 



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. 



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. 269, 270). The mem- 

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

 space is occupied by perilymph. The membranous labyrinth (fig. 269) 

 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 branches of the auditory nerve pass to certain parts only of 

 the membranous labyrinth, viz. : the maculae of the utricle and 

 saccule ; the cristae of the ampullae, and along the whole length of the 

 canal of the cochlea (the shaded parts in fig. 2691. 



