498 
DR J. STUART THOMSON ON THE MORPHOLOGY OF THE 
of the pallial tract as described by Johnston, but the former constitute the only 
trace of a similar condition so far as I have found it in Spinax. The small dorsal 
fibres, which one observes in my fig. 9, may only be branches of the olfactory or 
pallial tracts, for I have been unable to find in Spinax such a comparatively, well- 
defined tract and commissure as figured by Johnston in Scyllium canicula (fig. 20, 
p. 76, Johnston). 
Tractus tasnise (of Johnston). — To the tractus taeniae of Edinger, Kappers, and 
others, Johnston has given the name tractus olfacto-habenularis, and has then 
described and figured “ fibres . . . probably not noticed before ” under the term tractus 
taeniae. In the case of Spinax, I have not been able to arrive at any clear distinction 
between these two tracts, which it is allowed are closely associated together, and in 
the explanatory lettering of my figures I have therefore used the term tractus taeniae 
in a comprehensive manner. 
Summary of Fibre Complexes. 
I may here briefly notice the summary of certain fibre complexes as given 
by Johnston. 
Commissura pallii anterior. — This term is used to include in Selachians all the 
fibre decussations in the roof of the telencephalon. This position distinguishes it 
from the anterior commissure on the ventral surface. It consists of the following : 
(a) the hippocampal commissure, ( b ) the corpus callosum, (c) decussating fibres from 
the “ area olfactoria lateralis ” and from the “ area olfactoria medialis.” The anterior 
pallial commissure as regards the sub-commissures (a) and (6) is apparently, to say 
the least, not developed to the same extent in Spinax as in the types investigated 
by Johnston. 
The Basal Fore-brain Bundle, consisting of the medial and lateral fore-brain 
tracts, the former including the tractus olfacto-hypothalamicus medialis, the “fornix” 
and somatic projection tract (part of the tractus strio-thalamicus of authors); the 
lateral chiefly composed of the thalamo-corticalis tract. 
The Stria medullaris (corresponding in part to the tractus tsenise of Edinger 
and other authors), in which he recognises seven separate bundles, including the 
tractus tsenise s.str., the tractus olfacto-habenularis lateralis, and the commissura 
pallii posterior. An adequate discussion of these bundles is beyond the scope of the 
present paper. 
The Commissura anterior. — The Selachian fore-brain is not favourable for the 
study of the anterior commissure. 
