140 



TWENTY-THIRD LECTURE. 



single or multiple long ciliae, as for example in the frog 



b — 



The olfactory nerve — we are already 

 familiar with its pale primitive fibres (Fig. 



194, 3, Fig- 195,/) from p. 196— gives off 

 branches as it ascends to the cell layer of 

 the regio olfactoria. The axis cylinder (Fig. 



195, e) proves to be finely striated. At last, 

 after losing their sheath, the primitive or 

 axis-cylinder fibrillar radiate upwards in a 

 brush-like manner, as exceedingly thin vari- 

 cose filaments (d). It is assumed that they 

 are connected with the descending, similarly 

 constituted finest processes of the " olfac- 

 tory cells " (c). 



This theory proceeded from M. Schultze. 

 The eminent investigator — he has, unfortu- 

 nately, been prematurely torn from us — could 

 not, however, bring forward a forcible proof 

 here, any more than with regard to the other 

 nerves of sense, after years of arduous hon- 

 est labor. One cannot avoid certain con- 

 clusions, therefore, that by the aid of im- 

 proved methods, the matter may subse- 

 quently become quite different. However, 

 this is my subjective view. 



Exner has more recently denied the differ- 

 ence between the epithelial and olfactory 

 cells. In contradistinction to him, Von 

 Brunn has subsequently subscribed to the 

 older view of Schultze. Brunn found Over the regio olfac- 

 toria a homogeneous boundary layer after the manner of 

 the retina (see below). It has pores for the olfactory cells 

 only. 



Let us now pass to the termination of the nervus acusticus, 

 and thus enter the most difficult department of modern his- 

 tology. 



C 



Fig. 195. — Probable 

 termination of the olfac- 

 tory nerve in the pike ; a, 

 olfactory cells : b, rods ; 

 r. lower varicose fila- 

 ments ; r, axis fibrillar in 

 the sheath f; d, spread- 

 ing out of these ; at — 

 wanting connection wiih 

 the same fibrillse, c. 



