Architectonic studies of the telencephalon of <i>Iguana iguana</i>

Abstract

Abstract With the atrophy of the aquatic olfactory organ and the increased complexity of locomotion, the amphibian telencephalon was reorganized from a structure dealing primarily with olfaction, to the reptilian structure functioning at four levels of organization. The primary olfactory centers are retained, and the posterolateral and medial basal regions become specialized as secondary olfactory centers. The anterolateral basal regions are reorganized as primary association centers of somatic information. A dorsal component develops due to the convergence of sensory modalities, and a ventral component develops which influences tectal centers. Three pallial elements are recognized which function as part of the primary and secondary association systems. The lateral pallial element (pyriform cortex) is functionally related to the secondary olfactory system. Part of the medial pallial element (dorsomedial hippocampal cortex) is functionally related to the secondary olfactory system while the other part (dorsal hippocampus) is related to the secondary association system. The secondary association system, which integrates all sensory modalites, has evolved along two lines in reptiles. The sauropsid line has lost the motor elements of the dorsolateral component of the dorsal pallium. The dorosomedial component of the dorsal pallium retained its motor elements and functions with the hippocampus as a transitional cortical structure. In the theropsid line, the motor elements of the dorsolateral component were retained in a system which bypasses the older tectal motor system.