Three species were studied, the rabbit, opossum and rat. Lesions of the main olfactory bulb caused terminal degeneration, assayed by the Fink-Heimer method, to occur in the ipsilateral olfactory tubercle, prepyriform cortex (including its periamygdaloid part), ventrolateral entorhinal area, and in anterior and posterolateral divisions of the cortical amygdaloid nucleus. The various parts of the ipsilateral anterior olfactory nucleus and the rostroventral end of the anterior continuation of the hippocampus (hippocampal rudiment) also received this projection. Lesions of the accessory olfactory bulb, which receives its sensory input from the vomeronasal (Jacobson's) organ, caused terminal degeneration to occur in the medial amygdaloid nucleus and in a posteromedial part of the cortical amygdaloid nucleus. This projection was conveyed by an accessory olfactory tract, which is accompanied in part of its course by a small nucleus, the bed nucleus of the accessory olfactory tract. The accessory olfactory tract is initially a part of the lateral olfactory tract but becomes increasingly indivuated at more posterior levels. It parts company with the lateral olfactory tract at the rostral end of the amygdaloid region, and, in addition to distributing to the medio-cortical amygdaloid region, it enters the stria terminalis to terminate in the bed nucleus of the stria terminalis in a small region bearing cytoarchitectonic resemblance to the medial amygdaloid nucleus. The topographic segregation of the areas of termination of the olfactory and accessory olfactory (vomeronasal) projections is suggestive of a functional dichotomy in the organization of the olfactory system...

The retinopretectal projection was investigated in the rat, mouse, rabbit and tree shrew primarily by means of the Fink-Heimer technique. The experimental animals survived for varying periods of time following unilateral eye removal. The retinopretectal projection in each species was predominantly contralateral. A dense field of terminal degeneration was observed in the nucleus of the optic tract and in the olivary pretectal nucleus in each of the species. A less dense projection was observed for the posterior pretectal nucleus in each species. A sparse projection to the anterior pretectal nucleus was observed in the rabbit and tree shrew but not in the rat or mouse. A dense, ipsilateral projection to the olivary pretectal nucleus was observed in the rat, mouse and tree shrew. A sparse, ipsilateral projection was found in the anterior end of the posterior pretectal nucleus in the rat, mouse and tree shrew and in the posterior part of this nucleus in the rabbit. In the tree shrew, a small amount of terminal degeneration was found in the ipsilateral anterior pretectal nucleus. The nomenclature used here is uniformly applicable among the species described.

The pattern of projection of the retina to the pretectal region and its retinotopic organization were investigated in the rat by autoradiographic and silver impregnation techniques for axonal pathways. The endings of retinal axons form three terminal fields in the pretectum in: 1, olivary pretectal nucleus (PO), bilaterally; 2, posterior pretectal nucleus (PP), bilaterally; and 3, nucleus of the optic tract (NTO), contralaterally. The following retinotopic pattern was observed in rats surviving peripheral retinal lesions and injections of 3H-proline in the same eye, when the positions occupied by terminal degeneration in Fink-Heimer stained sections were matched with the corresponding areas deficient in radiolabel in adjacent autoradiographic sections showing the surviving parts of the terminal fields. The nasal periphery of the retina maps along the adjoining edges of PO and PP, both of which extend obliquely, in a posterolateral direction, through the entire extent of the pretectum. Both nuclei map the line of representation of the anterior midline (in the temporal retina) along their opposite edges (anterolaterally, in PO; posteromedially, in PP). This mirror-image symmetry is completed by the representation of the ventral peripheral retina separately in the rostral poles and the dorsal peripheral retina separately in the caudal poles of both nuclei. The map in NTO is vertically oriented, with the temporal retina, dorsally, the nasal retina, ventrally, the ventral retina, rostrally, and the dorsal retina caudally represented. The binocular area of the terminal field in PO is subdivided by a terminal-free zone into two parts that may process separately events in the central and lateral visual field.