a system of fine, unmyelinated fibers apparently originating from small-cell nuclei of the tuber cinereum, especially the arcuate nucleus, and terminating in the median eminence of the infundibulum, in contact with modified ependymal cells and the capillary tufts from which the hypothalamohypophysial portal veins originate.pituitary gland, neurosecretion. SYN: tractus tuberoinfundibularis.