172 Journal of Comparative Neurology. 



and soon the olfactory nerve fibres extend mesad. The devel 

 opment of a moniliform series is very obvious. Instead of 

 reaching the front of the cerebrum, as in other vertebrates, the 

 lateral aspects are reached. Even before the nerves effects en- 

 trance into the walls of the cerebrum the latter become concave. 

 In this way is formed the large olfactory fossa which is the 

 most remarkable peculiarity of the rhinencephalon of Ophidia. 

 The tuber as such is not developed but the olfactory structures 

 occupy the ventrolateral aspects of the frontal protrusion of the 

 brain, while the mesal wall is simply thinned out. The develop- 

 ed of the glomerulary structures has not yet been followed in 

 detail but it seems probable that a number of neuroblasts actu- 

 ally adhere to the cerebral surface and penetrate it. 



If we are correct in believing that all nerve tracts and 

 trunks are derived from moniliform adhesions it is not a matter 

 of so vital importance what source the successive elements of a 

 series may have had. 



In this connection we call attention to the following points 

 respecting the olfactory from another group. 



The relations of the olfactory apparatus of mammals may 

 be particularly well demonstrated in mouse embryos at the stage 

 when the vibrissae are in process of early development. The 

 specific olfactory apparatus in the epithelium need not be de- 

 scribed, but the fibres arising from the ganglion cells of the ol- 

 factory epithelium may be traced back as one continuous cord 

 with an occasional sheath corpuscle attached until it enters the 

 inter cranial space, here the fibre loses its sheath in 'the glom- 

 erulary mass This mass seems to contain, ist, sheath-form- 

 ing corpuscles ; 2d, corpuscles of the same sort as those which 

 occupy the vicinity^ of the ventricles. The fibre, after passing 

 into the glomerulary zone, subdivides dichotomonsly and is lost 

 among the " protoplasmic processes " of the specific olfactory 

 cells. It is as yet uncertain whether the latter are developed 

 from the tuber (pes) or are an integral part of the pero brought 

 thither by the proliferating olfactory epithelium. 



There is a cell-less interval separating the specific olfactory 

 cells from the glomerulary zone in which the fine branches of 

 the former can be readily seen. The axis-cylinder process 

 passes into a stratum just peripherad of the dense layer of (nu- 



