646 
ME. W. H. ELOWEE ON THE CEEEBEAL COMMISSUEES 
transverse band. This band, lying at the bottom of the great longitudinal fissure of 
the cerebrum, is the one previously mentioned as the superior transverse commissure. 
Traced outwards, its fibres, spreading into an extremely thin layer, form the upper 
and inner boundary of the superior portion of the lateral ventricle. They have a regular 
curve, outwards, upwards, and finally inwards, losing themselves in the medullary sub- 
stance of the hemisphere at its upper and inner angle. Their internal concave border 
is in contact with a fold of cortical grey matter, surrounding a deeply penetrating sulcus, 
which from the very bottom of the longitudinal fissure runs outwards and then upwards 
in the hemisphere, and which, as shown in the previous section, is continuous with the 
hippocampal sulcus in the posterior part of the hemisphere. The lateral ventricle, as 
seen in this section, is prolonged to a considerable height in the hemisphere, but other- 
wise its relations are similar to those of the same part in the placental mammals. 
Figs. 3 & 4, Plate XXXVIII. are taken from the brain of the Wombat ( Phascolomys 
vombatus). In general form the cerebral hemispheres are more depressed and elongated 
than those of the Kangaroo, and the temporal lobe obtains a comparatively slight 
development. Corresponding with this general elongation, the ventricular aperture 
and the surrounding parts have a wider curve backwards. The essential characters are, 
however, precisely the same. The anterior commissure attains an equal magnitude. 
The superior transverse commissure has the same form and relations, and the con- 
tinuation of the hippocampal sulcus extends above it, though it is not prolonged to 
quite the same extent on the anterior lobe. Seen in transverse section, the septum is 
narrower from side to side. 
The large carnivorous Marsupial, the Thylacine ( Thylacinus cynocephalus), so widely 
separated in external characters from both the Kangaroo and Wombat, shows the same 
general peculiarities of cerebral organization, but attended with a smaller development 
of the superior transverse commissure, especially of its anterior part, and a greater reduc- 
tion of the thickness of the interventricular septum (see Plate XXXVIII. figs. 5 & 6). 
Dissections of the brains of Phalangista vulpina and of Didelphis virginiana have 
yielded similar results, so that it may be presumed that the principle upon which the 
cerebral commissures are arranged is uniform throughout the Marsupial Order. 
Of the two genera of Monotremes, I have only had the opportunity of dissecting the 
brain of one, the Echidna. This most remarkable brain, with its largely developed and 
richly convoluted hemispheres, conforms in the main with the Marsupial type in the 
disposition of the commissures, but in detail presents a still further deviation from the 
ordinary mammalian form. As seen in Plate XXXVIII. fig. 7, the anterior commissure 
is as large relatively as in the Marsupials. Above it is seen the section of the superior 
transverse commissure, very much reduced in extent, and in which the two portions, 
upper and lower, observed in the Kangaroo are no longer distinguishable. Its relations 
to the hippocampal sulcus, to the ventricular aperture, to the columns of the fornix, to 
the precommissural fibres, and to the lateral ventricles are however the same, so that 
whatever parts of the placental mammalian brain are represented by this commis- 
