The paleostriatal complex (PC) of the pigeon lies in the basolateral wall of telencephalon, and consists of three major subdivisions: the paleostriatum augmentatum (PA), paleostriatum primitivum (PP), and nucleus intrapeduncularis (INP). The lobus parolfactorius (LPO) lies on the medial aspect of PA and has often been considered to be part of PA. The present study of afferent and efferent connections of the paleostriatal complex supports earlier Previous suggestions that the PC is directly comparable to the basal ganglia of mammalia. High concentrations of acetylcholinesterase were found in the PA, LPO and INP. Intense yellowish green fluorescence, probably dopamine, was confined to the PA and LPO.Stereotaxic lesions were placed in either the dorsal ventricular ridge structures above the PC ( n e e and hyperstriaturn), PA, LPO or PP-INP, and animals sacrificed from one to six days postoperatively. The brains were stained with the Fink-Heimer methods for the demonstration of degenerating axons and terminals. The region of the neo-and hyperstriatum was found to project upon the PA, in a seemingly topographic manner. PA was found to project topographically upon the PP and INP. In contrast, the LPO contributed to the medial forebrain bundle, terminating in the rostral lateral hypothalamus. LPO does not appear to project to the PP or INP.Lesions of PP-INP resulted in massive degeneration of a descending tract, the ansa lenticularis. Terminal degeneration was found in the anterior and posterior nuclei of the ansa lenticularis of the ventral diencephalon, nucleus dorsalis intermedius posterior and nucleus spiriformis lateralis of the dorsal thalamus, and the nucleus tegmenti pedunculopontinus pars compacta et disseminata of the isthmic tegmentum. In these several features of histochemical and hodological organization the PC alone appears similar to the caudate-putamen and globus pallidus complex of mammalian brains.More specifically, the PA resembles the caudate-putamen, whereas PP and INP resemble the external and internal divisions of the globus pallidus, respectively. Similarities and differences between avian and mammalian brains, and the relationship of the present study of the PC and previous studies of the dorsal ventricular ridge structures are discussed (Karten, '69; Nauta and Karten, '70).
