760 Dr- J BEARD, 



is the region of the socalled „anterior neuropore ^)". — This portion of 

 epiblast with a piece of the adjoining fore-brain (fb) is given under 

 much higher power in fig. 16. As this latter figure is a better repre- 

 sentation of nature then the former, the reader must only consider 

 fig. 17 as a guide to the situation from which fig. 16 is taken. 



It is noticeable that a certain number of cells fill in the space 

 between the two lips of the neural tube, and that outside them there 

 lies a number of other cells which obviously were split ofi" from the 

 epiblast in the fashion I have only recently described for a typical or 

 spinal ganglion (37). 



In fact , these cells {ol. a. n) are the foundation of the olfactory 

 neural ganglion^), which only differs from other neural ganglia in 

 that all its cells become converted into nerve fibres. 



The cells mentioned above are not connected with the fore brain, 

 though they partly lie between its lips. Soon they grow outwards 

 and downwards to the olfactory epithelium, which is not very far 

 distant, and in the figure is very possibly included in the portion of 

 epiblast at x. 



It is not easy to make out the very first differentiation of the 

 olfactory epithelium. The next stage at which I found it is figured 

 in fig. 20 under low power, and a portion of the right hand side of 

 the section is given in fig. 18 highly magnified. The fore brain {fh) 

 has already closed, the olfactory epithelium (o e) is well marked, but 

 as yet is it is not easy to make out the limits of its neural and hae- 

 mal extensions. A number of cells of the olfactory ganglionic foun- 

 dation are fused with the sensory epithelium. The ganglion has, as 

 yet, no connection with the central nervous system. The next stage 

 in the formation of the olfactory organ and its nervous apparatus is 

 depicted in fig. 19. The plane of section is rather horizontal, and 

 cuts the olfactory epithelium near its neural border ; so that the figure 

 of the sensory epithelium looks rather like a very much thickened 

 patch of epiblast. In reality the section is through the upper wall 

 of an open vesicle. 



The olfactory neural ganglion is fused with the sensory epithelium, 

 a rapid proliferation of cells is taking place, and some of these cells 



1) The anterior neuropore is a structure whose only morphological 

 importance rests in the support it affords to certain speculations. 



2) For an explanation of the terms neural and lateral ganglia the 

 reader is referred to Part I of the researches on the peripheral nervous 

 system (37, pp. 176—181). 



