The retinofugal pathways in the primitive African bony fish Polypterus senegalus (Cuvier, 1829).

Retinal projections were studied using Fink-Heimer and radioautographic methods in Polypterus senegalus, a species which is representative of a small group of African fresh-water bony fish often considered to be very primitive. The large optic nerve showed partial decussation at the chiasm. Two major contralateral tracts were observed: the axillary and marginal optic tracts, with the latter being subdivided posteriorly into the tractus opticus medialis and tractus opticus lateralis. The retina projected onto the: (1) hypothalamus (area optica postoptica); (2) thalamus (nucleus opticus dorsolateralis thalimi, nucleus dorsomedialis thalami, corpus geniculatum laterale, area optica dorsolateralis thalami, area optica ventrolateralis thalami); (3) pretectum (nuclei commissurae posterioris, pretectalis ventralis, pretectalis dorsalis); and (4) optic tectum (stratum marginale, stratum opticum, stratum griseum et fibrosum superficiale, stratum griseum et album centrale, stratum griseum et fibrosum periventriculare). Ipsilateral retinal projections were demonstrated to the same 4 levels and more precisely to the nucleus opticus dorsolateralis thalami, area optica dorsolaterale thalami, nucleus commissurae posterioris, stratum marginale and stratum griseum et album centrale. The existence of a retinal projection to the mesencephalic tegmentum is discussed. Comparing the primary optic system of Polypterus with that of other jawed vertebrates, and particularly with that of other bony fish, indicated that this species possesses a combination of characteristics which are both actinopterygian and sarcopterygian. The phylogenetic significance of this mozaic anatomical arrangement is discussed.

[Radioautographic analysis of retinofugal projections in the primitive bony fish Polypterus senegalus C]. / Analyse radioautographique des projections rétiniennes chez le poisson osseux primitif Polypterus sengalus C.

Retinofugal pathways of Polypterus senegalus C. have been examined by means of the radioautographic method. Contralaterally the retina projects to the hypothalamus, thalamus, pretectum and tectum. An important ipsilateral component has been observed. No retinal projection to the mesencephalic tegmentum has been identified. Comparing the primary optic system of Polypterus with that of other body Fish, indicates that this species possesses a combination of characteristics which are both actinopterygian and sarcopterygian. The significance of this mozaic arrangement is discussed.