Neocortical projections to the mesencephalon of the armadillo, dasypus novemcinctus

Abstract

The results of this study indicate a definite pattern of neocortical projections to the mesencephalon in the nine-banded armadillo. This pattern closely parallels that described for certain other mammals, but differs in certain specifics. Degenerating fibers resulting from a lesion of the mid-presupraorbital neocortex assumed a position within the most medial aspect of the cerebral peduncle and projected to the ventral and medial areas of the mesencephalon. Such areas inccluded the ventral nucleus of the periaqueductal gray, the rostal linear nuclei, the ventral tegmental area of Tsai, the medial substantia nigra and the rostral cap and intermediate portion of the red nucleus. The rostral tip of the neocortex, while projecting to similar mesencephalic areas as the mid-presupraorbital neocortex, did not distribute to either the ventral nucleus of the periaqueductal gray or to the red nucleus. The projection pattern of the neocortex immediately rostal to the supraorbital sulcus was also similar to that of the mid-presupraorbital cortex but, in addition, fibers distributed to the dorsal lateral tegmentum. Degenerating fibers which emanated from lesions immediately caudal to the supraorbital sulcus were positioned within the intermediate areas of the ipsilateral cerebral peduncle and terminated within the intermediate substantia nigra, the rostral cap and intermediate portion of the red nucleus, the mesencephalic reticular formation and extensively within the dorsal lateral tegmentum of the midbrain. Injured fascicles resulting from a lesion of the caudal one-third of the neocortex were located in the more lateral portion of the cerebral peduncle and projected to the more dorsal portions of the mesencephalon, as well as to certain mesencephalic areas which received cortical inout from the cortex immediately caudal to the supraorbital sulcus. A small ablation of the most caudal pole of the neocortex gave rise to degenerating fascicles which assumed a position within the most dorsal and lateral portion of the cerebral peduncle and terminated within the superficial layers of the superior colliculus.