94 
MR. OWEN ON THE STRUCTURE OF 
Structure. 
Fig. 3. Brain of the Beaver, with the substance of the hemispheres removed to the 
level of the corpus callosum. 
4. Brain of the Wombat, with the substance of the hemispheres removed to 
the level of the hippocampal commissure, except on the right side, where 
part of the thin internal wall of the lateral ventricle is left. 
5. Brain of the Beaver, with the left cerebral hemisphere cut down to a level 
with the commissure of the hippocampus, and the lateral ventricle ex- 
posed. The corpus callosum has been vertically divided, and the left half 
removed, together with the hemisphere : the right hemisphere is entire. 
6. A similar dissection of the brain of the Kangaroo, with the right hemisphere 
entire, and turned aside, showing the absence of the hemispheric commis- 
sure, corresponding to the corpus callosum of the Beaver. 
The small size of the corpus striatum, r, as compared with the Wombat 
and Beaver, is shown in this view. The posterior bigeminal bodies are the 
broadest, the anterior the longest, in this animal as in the Beaver and 
Wombat. 
PLATE VII. 
Fig. 1 . A vertical bisection of the brain of the Opossum ( Didelphys Virginiana, 
Shaw), showing The large proportional size of the anterior commissure,?/. 
2. A vertical bisection of the brain of a Goose. 
3. A lateral section of the left hemisphere, showing the lateral ventricle and 
hippocampus major in the Opossum. 
The roof of the lateral ventricle is raised, showing it to be formed by 
fibres arching over the hippocampus, and continued from the inner margin 
of that part into those which radiate from the corpus striatum externally. 
4. A similar dissection of the brain of the Kangaroo. 
In this species the roof of the ventricle is proportionally thicker than 
in the carnivorous Opossum. Besides the diverging fibres of the crus 
cerebri, and those which pass in an arched form from the inner border of 
the hippocampus, over that body to the corpus striatum, there are others 
which form a thin layer, and pass into the taenia hippocampi, closely 
embracing the hippocampus : some of these are shown at x x. 
The general disposition of the hemispheric fibres is such, that, supposing 
them contractile, they would draw the superficies of the hemisphere to- 
wards the crus cerebri, as to a fixed point, and compress the bodies pro- 
jecting into the ventricles. 
5. A similar dissection of the brain of the Ass. The dotted line shows the ex- 
tent of the corpus callosum. 
