Retinal projections in two crocodilian species, Caiman crocodilus and Crocodylus niloticus

The retinal projections of Caiman crocodilus and Crocodylus niloticus were investigated by means of the orthograde axonal transport of either rhodamin e beta-isothiocyanate or tritiated proline. In these two species, each trac er revealed contralateral retinal projections to three hypothalamic regions (subventricular gray matter, nucleus suprachiasmaticus, and area optica hy pothalami lateralis), five thalamic regions (nuclei ovalis, dorsolateralis anterior, ventrolateralis and ventrobasalis, and lateral geniculate complex , of which six subcomponents can be distinguished), six prerectal regions ( nuclei posterodorsalis, lentiformis mesencephali, griseus tectalis, genicul atus pretectalis, area optica commissurae posterior and area optica pretect alis lateroventralis), six outermost layers of the optic tectum, and the nu cleus opticus tegmenti. Weak ipsilateral retinal projections have been obse rved in two hypothalamic nuclei and in the nucleus opticus tegmenti. Compar ative analysis with other data show that the contralateral retinal projecti ons of crocodiles are considerably more reptilian than avian. Moreover, cro codiles share with birds an extremely poor contingent of ipsilateral retina l projections.