On a peculiarity of the cerebral commissures in certain Marsupialia, not hitherto recognised as a distinctive feature or the Diprotodontia

Abstract

It has been known for a considerable time that some of the fibres of the ventral commissure of the cerebrum in certain Marsupials dissociate themselves from the rest of the commissure as soon as they have crossed the mesial plane; and that, instead of passing bodily into the external capsule, which is the usual course of the fibres of the ventral or anterior commissure, they form an aberrant bundle which associates itself with the internal capsule so as to reach the dorsal area of the neopallium by a shorter and slightly less circuitous course (fig. 2). This peculiarity was represented in the drawings of sections through the brains of Macropus and Phascolomys , in 1865, by the late W. H. Flower. It was more distinctly shown in a diagram illustrating a coronal section through the brain of a Derbian Wallaby which was published 27 years later by Johnson Symington.