XIII. On the commissures of the cerebral hemispheres of the marsupialia and monotremata as compared with those of the placental mammals

Abstract

The terms used in describing the anatomy of the vertebrated animals have in most cases been originally bestowed on parts of the human body, being frequently derived from some quality, relation, or real or fancied resemblance to some known object, possessed by the structure in question in Man. It will therefore be most convenient to pass from the best to the least known, and to commence by a short recapitulation of the characters and relations, in the human brain, of those parts to the consideration of which, in the brains of the lower mammalia, this communication is specially devoted. Plate XXXVI. fig. 1 is a view of the inner surface of one of the hemispheres of the human cerebrum, such parts as pass across the middle line to the other hemisphere having been divided, and those that do not belong to the hemisphere proper being removed. A convenient central point to start from in the description is the part cut through to make the section last referred to. A is the surface of the divided mass of fibres, by which the hemisphere is connected with the inferior parts of the encephalon, and with the spinal cord—the crus or peduncle of the brain. The section is made between the corpus striatum and the thalamus opticus. The thalamus, as not belonging to the hemisphere proper, and interfering with the view of essential parts, is removed.