122 Journal of Comparative Neurology, 



bundles) break up into small fascicles and lie parallel to the 

 ventro-lateral margin. They seem to receive fibres from the 

 large pyramidal cells of that region and to continue to the 

 cephalo-dorsal region. Fig. 12. illustrates a few cells from the 

 optic lobe, from the deeper tectum layers. The arrows ^' and d 

 indicate the directions ventrad and dorsad respectingly. Fig. ij. 

 is part of the dorso-median region at the level of the front of the 

 optic lobes. ;r is a cell in the optic tract which is shown more 

 highly magnified in Fig. 14.. No attempt is here made to dis- 

 cuss the arrangement of tracts in the mesencephalon. 



The olfactory tuber in the frog has been studied by deeply 

 staining with haematoxylin with results which closely correspond 

 with those of Retzius and others by use of the Golgi method. 

 The haematoxylin method has the advantage of .permitting com- 

 plete orientation. The elements of the rhinencephalon are very 

 simple. About the ventricle we have the same relations which 

 prevail in other regions of the fore brain. The elements of the 

 olfactory ganglionic layer, or specific cells of the tuber, vary 

 greatly in size but consist of a more or less bipolar cell body 

 enclosing a nucleus nearly occupying its transverse diameter. 

 Two processes of considerable size are developed, one from the 

 peripheral or cephalic extremity, the other from the ental end. 

 The former in many cases can be traced into a glomerule where 

 it breaks up by dichotomous branching to intermingle with sim- 

 ilar branches from the olfactory nerve. The other processes ex- 

 tends caudad beyond the limits of the tuber, beyond which we have 

 thus far not succeeded in tracing the isolated fibre. In other 

 cases the cell, while it has the form just described, seems to 

 have its relations only within the pero and cannot be proven to 

 give rise to an axis cylinder. Fig. 3, Plate XX, illustrates the 

 typical olfactory neuron in the frog. Often the axis cylinder 

 can be traced farther than in the case figured. While it has 

 not proven possible to trace separately the various fibres of the 

 olfactory neurons, it is easy to follow their combined course. 

 Collecting on the caudo-lateral aspect of the pero these fibres 

 form a strong radix which passes, by a strong lateral sweep, 

 caudad and dorsad to a point behind the entrance of the ped- 



