376 PRACTICAL HISTOLOGY. [XXXIII. 



process. The free surface of the cell is covered by a clear hem, but 

 its exact constitution and significance are unknown. 



(c.) There may also be found large granular polygonal cells 

 derived from Bowman's glands their acini and ducts. 



ADDITIONAL EXERCISES. 

 Olfactory Bulb. 



1. This is a very complicated structure, and has been investigated recently 

 by Golgi and K. y Cayal. The bulb of a new-born animal is hardened by 

 Golgi's rapid method and sections made. It contains a layer of white ncrve- 

 fibres, and under this large nerve-cells mitral cells and one remarkable 

 arrangement known as olfactory glomeruli, which are nests of fibrils, formed 

 partly by the terminal arborisations of the processes of mitral cells and by non- 

 medullated nerve-fibres of the olfactory nerve, which are passing onwards to 

 terminate in tlie olfactory epithelium. 



2. Olfactory Eegion by Golgi's Method. The mucous membrane of the 

 ol factory region is placed for 7 days in Golgi's osmico-bichromate fluid, then in 

 silver nitrate, and hardened in alcohol. One often fails, but if a successful 

 preparation be obtained the ends of the olfactory nerve are seen passing into 

 the olfactory cells. 



3. T.S. Nose. Harden the whole nose of a mouse in Miiller's fluid, stain in 

 bulk in borax-carmine, and make T.S. across the whole organ to show its 

 walls, septum, turbinated bones, respiratory and olfactory regions. In such 

 animals as possess a well-developed organ of Jacobson study it. In it also, 

 if a young animal, will be found beautiful sections of developing tooth. 



LESSON XXXIV. 



TERMINATION OF NERVES IN SKIN AND SOME 

 MUCOUS MEMBRANES. 



Sensory nerve-fibres terminate in the skin and mucous mem- 

 branes in three ways : 



(I.) Free nerve-endings, i.e., by intra-epidermic fibrils. 

 (II.) In special terminal corpuscles. 



(III.) In neuro-epithelial cells, i.e., specially modified epithe- 

 lial cells, as the rods arid cones of the retina, the 

 auditory hairs in the ear, the inner cells of taste-buds 

 and olfactory cells. 



I; Free nerve-endings occur especially in stratified epithelium, 

 e.g., in the skin, mouth, and cornea (Lesson XXXII.). The norve- 

 fibres lose their myelin and primitive sheath, and the axis-cylinder 



