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.