Anatomical and experimental study of certain association fascicles in the cortex of the rabbit (Oryctalagus...

1. All lesions resulted in degeneration of the short intracortical association fibers in cortical layer I and of the short subcortical fibers which extended to the corona radiata before ending in the deeper layers of the overlying neopallium. 2. From all the lesions fibers were traced through the corona radiata to the subcallosal or the so-called superior fronto-occipital association bundle. This bundle had projection fibers to the orbitofrontal cortex. 3. From the lesion in the orbitofrontal neopallium, the orbitofrontal-pyriform connections were established. Such fibers coursed on the dorsal edge of the lateral olfactory tract and distributed to the pyriform cortex and to the nucleus of the lateral olfactory tract. 4. The uncinate fasciculus of man derived its name from its arching course from the base of the frontal lobe to the temporal lobe. Because of the more caudal position of the amygdala in the rabbit, the comparable fasciculus passed directly caudally and exhibited only slight arching. This fasciculus in the rabbit had the typical dorsal and ventral parts. The dorsal part arose from the orbitofrontal cortex to distribute to the pyriform and the temporal lobe cortices. The ventral portion extended into the olfactory tuberculum and the anterior amygdaloid area. 5. The paraventricular component of the transverse frontal fasciculus interconnected the neopallium with the medial part of the olfactory tuberculum. It had origins in the frontal and possibly in other neocortical areas. 6. The cingulum interconnected the medial portion of the olfactory tubercle, the septum, the various cingulate areas and areas of the neopallium with each other. 7. Therefore, the New Zealand white rabbit had short association fibers which were mainly neopallial in origin and termination and long association fibers which had both a neopallial and a limbic component.