374 PRACTICAL HISTOLOGY. [XXXIII. 



which arises from the lamina spiralis ossea, and spreads over so 

 as partially to cover the organ of Corti. The organ of Corti con- 

 sists of two rows of pillars inner and outer the rods of Corti 

 which meet above, forming arches, and leave a three-sided tunnel 

 between them. Internal and external to these are rows of cells, 

 some of them provided with fine bristles hair-cells constituting 

 the cells of Corti and Deiters. Some of these cells are the actual 

 terminal end-organs of the cochlear nerve, and others are susten- 

 tacular in function. The scala vestibuli and scala tympani com- 

 municate at the apex of the cochlea, as shown in fig. 342, V.T. 



(H) Observe the rods of Corti, the inner more numerous than 

 the outer, and how the head of the one lies over the head of the 

 other. The rods vary in length and span, in different parts of 

 the cochlea.- Internal to the inner rods is a single row of hair- 

 cells, and external to the outer rods are several rows of hair-cells. 

 Between the latter are supporting cells, and beyond them are 

 columnar epithelial cells (fig. 343). The rods and hair-cells are 

 covered by a special membrane, seen in section, which is perforated 

 by the upper ends of the hair-cells membrana reticularis the 

 basilar membrane terminating towards the wall of the cochlea in a 

 fibrous expansion, the spiral ligament. 



The student must give considerable time and attention to the 

 subject if he wishes to get preparations showing the structure of all 

 the parts. It is difficult to keep the parts from falling asunder, and 

 if the ear be not properly decalcified, bubbles of gas are discharged 

 within the cochlea, which rupture the finer parts ; hence arises the 

 necessity for opening the cochlea and fixing the parts with a " fix- 

 ing" medium previous to decalcifying it. 



4. Semicircular Canals. Fix the membranous semicircular 

 canals, and their ampullae, of a skate in Flemming's or Fol's fluid. 

 Harden in alcohol. In the ampullae are the terminations of the audi- 

 tory nerve in the crista acustica. Make T.S. of the canals and V.S. 

 of the crista acustica ; in the latter case take care to include the 

 entrance of the nerve- fibres. The preparation of suitable specimens 

 to stain the termination of the nerves in the crista acustica presents 

 very considerable difficulties. The student may have to repeat the 

 process several times if he wishes to get typical specimens. 



THE NOSE. 



5. Olfactory Mucous Membrane. Divide longitudinally the 

 head of a freshly-killed rabbit. Place small pieces of the olfactory 

 mucous membrane readily recognised by its brownish colour 

 in dilute alcohol (2 hours), and then in i per cent, osniic acid 



