Comparative neuroanatomical evidence and the taxonomy of the tree shrews (Tupaia)

Abstract

Recent neuroanatomical literature and its relationship to the taxonomic question of Tupaia is reviewed. The origin, course and terminations of corticospinal fibers in the tree shrew is intermediate between that of the opossum and phalanger, representing more basic forms, and the slow loris and greater galago. The terminations of the optic tract in the dorsal lateral geniculate nucleus share some characteristics with the hedgehog and greater galago. The organization of the accessory optic system is distinctly basic in the tree shrew. The cerebral cortex and corticofugal fibers of Tupaia are intermediate between that of basal forms and some Prosimii. The so-called phylogenetic increase in brain stem centers and the degree of encephalization of Tupaia is intermediate between advanced insectivores and various members of the Lorisidae and Lemuridae. The cerebellum of Tupaia has a poorly developed anterior lobe, and a well developed hemisphere of the posterior lobe, interpreted as basic and moderately advanced characteristics respectively. The deep cerebellar nuclei of the tree shrew more closely resemble those of the hedgehog and mole than those of the lesser galago. The vascular pattern of the rhombencephalon is, in general, similar to that of some Prosimii. The diversified results of comparative studies on the tree shrew central nervous system do not suggest a tupaiid-primate or a tupaiid-insectivore affinity but tend to support the separate order suggestion of Straus.