Efferent connections of the caudate nucleus in the Virginia opossum

The efferents of the opossum's caudate nucleus were investigated by charting the the fiber degenerations produced by electrolytic lesions in various parts of this nucleus. By the aid of a modified Fink-Heimer procedure, degenerating fibers were traced from each of the lesions to the small globus pallidus in which they appeared to be distributed in an orderly dorsoventral pattern. Fibers from all lesion sites in the caudate nucleus were found to terminate in the entopedunucular nucleus. In the substantia nigra, caudatofugal-fiber degeneration was confined in all cases to the rostal part of the pars reticulata, and was densest in the medial one-half of this nucleus. Only from lesions in the ventromedial part of the caudate nucleus could degenerating fibers be traced to the nucleus ansae lenticularis. No fiber degeneration could be traced rostrally from the lesions, or to the putamen, red nucleus, subthalamic nucleus, or pons.