CELLS OF THE NERVUS TERMINALIS OF THE R.\T 103 



laterad of the medial edge of the depression comprising the pit, 

 and has been followed through six sections. Evidently, then, 

 the earhest proliferations from the olfactory epithelium are in 

 the territory presumably of the future septal epithelium. This 

 early outgrowth is illustrated in figure 1. The figure is taken 

 from a photograph, slightly retouched. The olfactory epithe- 

 lium, using this term to designate the general epithelium lining 

 the olfactory sac rather than restricting it to the later highly 

 specialized sensory epithelium, has thickened somewhat over 

 the preceding stage, but its actual maximum number of nuclear 

 rows is difficult to ascertain on account of the plane of section. 

 The proliferation figured is situated amid two vascular channels 

 and is intermingled with the condensing mesenchyme. Nevei'- 

 theless, it is seen that the cells budded off from the epithelium 

 are elongate and that one (n) clearly possesses a process extend- 

 ing peripherally into the olfactorj'- epithelium for a considerable 

 distance. The nuclei are elongated, ovoid, or kidney-shaped. 

 At this stage, the ramus ophthalmicus trigemini appears no 

 more extensive than in the former one. Certain of its spindle- 

 shaped cells show a tendency to round out and their cj^toplasm 

 is acquiring the darkly staining characteristic of the neuroblast. 

 The ophthalmicus does not approach the zone of proliferation 

 from the olfactory epithelium, nor does the maxillaris. Con- 

 tributions from other of the above-mentioned possible sources 

 are even more absolutely excluded at this time. The relation 

 of the spindle-shaped cell (n), should no further migration occur, 

 is suggestive of the relations of the ganglion cells in the sub- 

 epithelial plexuses, in the so-called terminal and septal territories 

 of Ayers ('19). 



In another embryo of the same litter, the process has gone 

 much further. The olfactory pit is present on one side as a deep 

 depression and on the other a contact is just in process of estab- 

 lishment with the oral epithelium, forming thereby a bucco- 

 nasal membrane. Evidences of proliferation from the epithelial 

 lining of the pit are abundant (fig. 2) and the result has been 

 the piling up of a mass of cells in a ganglion-like aggregate (g). 

 The shape of the aggregate is somewhat that of a disc, conform- 



