The object and scope of this paper are to detail the results of a full investigation into the minute structure of the cerebral cortex in the Pig, and to add such notes upon the histology of the same structure in the Sheep and Cat as will suffice for a fair comparative view of those divergencies in fundamental structure which present themselves between the brain of these animals and that of the highest members of the Mammalian series. Attention has been especially directed to the greater mass formed by the parietal, frontal, and upper arc of the limbic lobe, the inferior arc of the limbic lobe (gyrus hippocampi) and the olfactory lobe being left for subsequent examination. The method adopted has been that of slicing the hemispheres of fresh brain from end to end upon the freezing microtome, and examining each individual section, both in the fresh state and after preservation, by a method already described. Tables containing details of the dimensions of cells and depth of layers accompany the paper, being collated at the end for convenience of reference. The Convolutions of the Brain In the Pig. The regional distribution of ganglionic cells in the cortex of this animal constitutes so important a portion of our inquiry that, in order to avoid any obscurity in the subsequent sketch, it will be advisable to review briefly the arrangement of the convolutions and sulci. In doing so I shall follow the terminology adopted by Professor Broca, in his late important work on the comparative anatomy of the convolutions in Mammals.