xxviii Journal of Comparative Neurology. 



true coronal fibres, however, pass through the lateral walls and the fibres 

 mentioned by Edinger are, according to Meyer, really fornix fibres. 

 To this it may be said that Edinger has recognized the fornix tract 

 and that the changes in the form of the ventricle in the various groups 

 are so great that it must be relied on with caution in morphological 

 determinations. It is a little strange that Meyer is apparently igno- 

 rant of the fact that the writer has given detailed descriptions of the 

 hippocampal commissure in a wide range of non-mammals and traced 

 the descending fibres of the fornix in reptiles and even fishes several 

 years ago. We do not see that because the peduncular fibres have 

 not. differentiated in the lower forms as they have in the higher mam- 

 mals it follows that there can be no homologue of the callosum. This 

 is but another illustration of the effects of too close reliance on an- 

 thropotomy, and reminds one of the remark once made to the writer 

 by a rising neurologist who said with an air of conviction, " But for 

 me, don't you know, the callosum must describe an arc — must be a 

 beam connecting something." The allusion was of course to the root 

 meaning of "trabs" or "Balkan." 



On the other hand the facts seem to us to fully justify the second 

 point made in the paper before us, i.e., that the septum is not an 

 atrophied cortical region but a part of the ganglionic base. This is 

 made more probable by the fact that this region, which, to avoid pre- 

 judice we have called intraventricular lobe, in the reptilian and am- 

 phibian brain, has a structure quite unlike that of true cortex. 



In a recent paper, G. Elliot Smith has discussed the same prob- 

 lem from a somewhat different stand-point. ^ 



We are left in the dark as to the criteria relied on by Smith to 

 distinguish the callosum, though he says that "it seems possible that 

 the corpus callosum appears in response to the demand for a shorter 

 connecting route between the rapidly developing dorsal portions of the 

 cortex cerebri." The intraventricular lobe or septum of reptiles the 

 author terms the precommissural area, objecting to the term septum 

 that the latter in higher mammals is merely the thickened lamina teri- 

 nalis. This area is a part of the rhinencephalon and accordingly the 

 commissural fibres passing through it cannot be callosal. 



Part of the anterior commissure is said to be the homologue of 

 the callosum, for it is characteristic of the objectors to the evident 

 homologies to strain at the gnat but swallow the camel. Still we have 



^Preliminary Communication upon the Cerebral Commissures of the Mam- 

 malia. Proceed. Lin. Soc. N^. S. Wales, Oct., 1894. 



