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Abstract

Two morphological traits of the anterior cerebellar lobe unique to the higher anthropoid primates are described, and a search for their possible origins is made among representatives of the major subdivisions of the Anthropoidea. One trait involves the gradual reduction and migration of lobule II until it ultimately becomes located upon and fused with lobule I. Hence, in the higher anthropoids, the lingula actually consists of lobules I and II combined. This reduction and migration of lobule II from its normal position places lobule III adjacent to the lingula in the location occupied by lobule II among other mammals. The second distinctive feature concerns the inclusion of the anterior cerebellar peduncle on each side into the anterior medullary velum, so that they form a continuous morphological unit, separate and distinct from the remaining components on the ventral surface. This modification is found only in the members of the Hominoidea. In addition, several observations upon certain ontogenetic changes in lobular structure are reported.