A Monograph of Orycteropus afer.—II. Nervous System, Sense‐organs and Hairs

Abstract

Summary. The external and internal anatomy of the brain have been described. Characters suggesting Ungulate affinities have been found in the gyrus ambiens, in the fissuration of the cortex and in the distribution of the cortical areas. Despite the high degree of osmatism, the brain as shown by the amount of cortical differentiation is by no means a very primitive one. On the other hand, it is much nearer the generalized type of Proto‐Oarnivore or Ungulate brain than is Sus communis, for instance. The brain of Orycteropus has advanced sufficiently far from the generalized type to suggest that it was advancing along the line of the Ungulates. The anterior olfactory nucleus appears to be the same structure which previous writers called the olfactory peduncle with its prolongation into the bulb. Since its cell type differs from the other secondary olfactory centres, and it is continuous with the cellular laminæ of the bulb, it more properly belongs to this structure than to the olfactory cortex. It is thought that the wide extent and pattern of the secondary olfactory cortex needs no other explanation than the response to the macrosmatism. The constitution of the amygdaloid nucleus conforms to the account given by Johnstone for other mammals.