si:ct. 



235-] 



OLFACTORY CELLS. 



605 



Fig 24S. 



\ 



lower ends, divide into two or even more filaments, which may 

 actually unite with those of neighbouring cells. The nuclei of 

 these cells are oval, with a small distinct nucleolus and granular 

 contents. The cells themselves, besides the ordinary granular 

 matter, include in each a certain number of pigment-molecules, 

 coloured yellow or brown, in various animals; on these the before- 

 mentioned colour of the olfactory region mainly depends. — Much 

 more difficult of investigation are the olfactory cells. These were 

 correctly described by M. Schultze as long spindle-shaped struc- 

 tures, containing a round clear nucleus, with a distinct nucleolus 

 and no pigment, and giving off from the opposite sides of the cell- 

 body two tine filiform processes. The outer process is somewhat 

 the thicker, passes between the broad portions of the epithelial 

 cells to the external surface, and is here provided w 7 ith a minute 

 process, resembling a fine short hair, projecting beyond the 

 epithelial cells. The inner process is a much more delicate fila- 

 ment, and can only be distinctly made out by a good microscope ; 

 in chromic acid preparations, it pre- 

 sents from place to place a number 

 of small dark varicosities, which 

 may occasionally be observed also 

 on the outer filament. The olfactory 

 cells appear to be arranged in a 

 simple manner around each epithe- 

 lial cell, and to form with their cell- 

 bodies the greater portion of the 

 middle and deeper strata of the 

 epithelial layer, while their inner 

 processes extend as far as the proper 

 mucous membrane ; it is a question 

 whether they there become con- 

 tinuous with the fibres of the olfac- 

 tory nerve. — In order to protect 

 this epithelium, and to keep it 

 moist, there are present iu the whole of the proper olfactory region 

 a large number of the glands of Bowman ; a circumstance which 

 is striking, as the portion of the ciliated mucous membrane imme- 

 diately adjoining contains very few, or is even entirely destitute of 

 glands. The glands of Bowman are simple cylinders, o - o8'" to 

 01'" long, either straight or slightly convoluted at the lower end ; 

 or else they have the form of extended pyriform tubes, which lie 

 in crowded rows, chiefly between the larger branches of the olfactory 



6[> 



I. From the frog; a. epithelial cells of 

 the regio olfactoria ; b. olfactory cells. 2. 

 Small branch of ihe olfactory nerve of 

 the frog, separating at one end into a 

 brush of varicose fibrils. 3. Olfactory 

 cell of the sheep. Magnified 350 times. 



