Decussation pattern at the optic chiasm
The optic nerves of the left and right eye cross at the optic chiasm. The cross-over can be partial or complete depending on the species. In marine mammals the decussation pattern at the optic chiasm has only been determined in the bottlenose dolphin so far revealing a complete cross-over. In this project we want to analyse the decussation pattern at the optic chiasm of two phocid seals using the fluorescent tracer DiI and 3D Polarized light imaging (3D-PLI, in cooperation with the Research Center Jülich). From previous research on the optokinetic nystagmus of harbour seals (Hanke et al. 2008) and from the frontal eye placement we expect to find a partial crossing at the optic chiasm of phocid seals.
Axon counts of cranial nerves
In this projects axons within the Nervus opticus, Nervus facialis, Nervus vestibulocholearis and Nervus trigeminus of harbour seals and hooded seals are analyzed and counted. The data are valuable for interspecific comparison and provide a rough estimate of the significance of specific sensory systems in different species.