388 



THE SKIN AND THE SENSE-OEGANS. 



Fis-. 



241. 



processes vary considerably in length, according to the position of 

 the body (o'03-o*o5 mm.). The central processes vary from 0'02- 

 0*03 mm. in length. The peripheral processes are considerably 

 thicker than the central processes. No mewhrana limitans olfactoria 

 has been discovered in the frog. 



(2) The second layer consists of a network of processes belong- 

 to the bases of the central processes of the superimposed epithelial 

 and olfactory cells. Numerous highly refractive nuclei possessing 

 nucleoli are situated in the meshes of this network ; they correspond 



in all particulars with the nuclei of the 

 olfactory cells (M. Schultze). According 

 to Exner the branched processes of the 

 epithelial cells and of the olfactory cells 

 unite to form a complex plexus. Other 

 observers, Paschutin, Cissoif, v. Brunn, 

 Schultze, and Hoffmann oj)pose this 

 view, and hold that the central processes 

 of the olfactory cells do not unite with 

 the processes of the epithelial cells, but 

 that they are in direct continuity with 

 the fibrils of the olfactory nerve. This 

 view is probably correct. 



The submucous layer has a loose con- 

 nective-tissue matrix, w^hich encloses the 

 glands, nerves, and vessels; according 

 to Paschutin two pigment-layers may 

 be distinguished : the one, immediately 

 under the middle layer of this mucous 

 membrane, is continuous and deeply pig- 

 mented; the second is deeper and does 

 not form a continuous layer. This layer 

 is extremely rich in blood-vessels and 

 lymphatics (Langer * and Paschutin), 

 (Fig. 240 II). The lymphatics are rela- 

 tively very large and are very nimtierous 

 (Langer). 



In this layer the central processes of the olfactory cells form 

 bundles of fibres, lying parallel with the surface of the mucous mem- 

 brane (Paschutin, Cissoff, and Schultze).] 



Separations from the olfactory mu- 

 cous membrane of Rana temporaria ; 

 after C. K. Hoffmann, 

 I. Surface view of the olfactory 

 mucous membrane. Magni- 

 fied 350 times. 

 Epithelial and olfactory cells. 



Magnified 600 times. 

 Epithelial cells. Magnified 600 

 times. 



II. 



Ill 



