372 MANUAL OF HISTOLOGY. 



branches into a number of delicate filaments, by means of 

 which the cell is attached to the fundamental layer of connec- 

 tive tissue. These widened extremities of the cells often con- 

 tain a brownish, partly nuclear, partly diffused pigment. 

 Viewed upon the plane surface, the number of olfactory cells 

 is apparently larger than that of the cylindrical cells. Each 

 one of the latter, however, is generally surrounded by six of 

 the olfactory cells, which completely fill the intermediary 

 spaces between the cylindrical bodies. Both varieties of cells 

 are so accurately adjusted to each other that, especially in the 

 wider portion of the epithelial cells, fine longitudinal furrows 

 may be seen, into which the peripheral continuations of the 

 olfactory cells have been received. 



The surface of the epithelium is covered by a delicate mem- 

 brane, discovered by Von Brunn, and called by him the mem- 

 brana limitans olfactoria. He has compared it to themembrana 

 limitans externa of the retina, and describes its free surface as 

 being plane and even, while its lower surface covers completely 

 the rounded terminations of the epithelial cells. The periph- 

 eral prolongations of the olfactory cells pass through this 

 membrane, and terminate with bare extremities at the level of 

 its free plane. 



The olfactory nerves. The branches from the olfactory 

 ganglia which emerge through the apertures of ,the lamina cri- 

 brosa are composed entirely of non-medullated filaments, which 

 resemble embryonic nerve-fibres. They next anastomose in the 

 deeper layers of the mucous membrane, and form a dense 

 plexiform meshwork, which sends fine branches toward the 

 surface. In these branches the axis-cylinders are broken up 

 into numerous, very fine, varicose fibrils, which ascend to the 

 limit of the epithelial layer, where they are lost. Most au- 

 thors agree with Schultze that there is a distinct connection 

 between the nerve-fibrils and the olfactory cells. Exner be- 

 lieves that the nerve-fibrils connect with the epithelial cells 

 also. He argues, moreover, that intermediary forms, between 

 the two varieties of epithelium, are found, which would prove 

 that they are not different structures, but one and the same. 

 Neither of these views has yet been established. 



Bowman' s glands, peculiar to the olfactory mucous mem- 

 brane, are found in it in large numbers. They occupy almost 

 the whole thickness of the mucous membrane, their bodies be- 



