Retino-hypothalamic Connexions in Cetacea

Abstract

THE existence of retino-hypothalamic neural connexions in mammalian forms has long been controversial. The more recent investigations of Blümcke¹ in the cat and guinea pig, of Frey² in the guinea pig and of Knoche^3,4 in man, dog and rabbit strongly suggest that a bundle of fibres leaves the optic pathway at a chiasmatic level and passes dorsalward into the area of the paraventricular nucleus of the adjacent hypothalamus and also into the posterior lobe of the hypophysis. Altman⁵, using the Nauta–Gygax staining technique to demonstrate fibre degeneration following optic nerve section in the cat, observed fibres of retinal origin above the optic chiasm and in the lateral hypothalamus immediately adjacent to the optic tract. Giolli⁶, on the other hand, using both the Nauta–Gygax and Romanes silver methods to investigate the accessory optic system in the cynomolgus monkey, found no evidence of retino-hypothalamic fibres in this form after enucleation of the eye.