title: The secondary olfactory connections in two chondrichthians, the shark Scyliorhinus canicula and the ray Raja clavata.
abstract: The secondary olfactory connections in the shark Scyliorhinus canicula and the ray Raja clavata have been studied with reduced silver techniques. After transections through the pedunculus olfactorius in Scyliorhinus degenerating fibers could be traced to the telencephalic hemisphere. On entering the hemisphere these fibers subdivide into a small medial and a larger lateral olfactory tract. The medial tract distributes fibers to the lateral part of the ipsilateral pallium dorsale, pars superficialis and area periventricularis pallialis, but the majority of its fibers terminate in the submeningeal zone of the pallium. The medial olfactory tract also projects contralaterally to the submeningeal pallial zone via the commissura olfactoria inferior and to the stratum granulare bulbi olfactorii by way of the commissura olfactoria superior. The lateral olfactory tract distributes mainly to the pallium laterale and to the region superficial to the lateral part of the area superficialis basalis, though the striatum also receives some fibers. In Raja the secondary olfactory tract could not be subdivided into medial and lateral components and its projections seem to be restricted to the ipsilateral pallium laterale. A striking difference between Scyliorhinus and Raja is that in the latter no contralateral projections could be recognized nor a projection to the area superficialis basalis. When these results are compared with those reported in the literature for other cartilaginous fishes, it appears that the secondary olfactory connections of Scyliorhinus are more extensive than in other chondrichthians studied experimentally. In some cases of peduncle transection in Scyliorhinus the lateral part of the striatum was also involved in the lesion. In addition to the pattern of degeneration seen after olfactory peduncle lesions, degenerating fibers could be distinguished both in the stria medullaris and basal forebrain bundle. The former projects to habenular nucleus, whereas the latter distributes to the hypothalamus, ventral thalamus, and brainstem tegmentum.
mesh_terms: D000818:Animals; D001931:Brain Mapping; D002490:Central Nervous System / Q000033:anatomy & histology*; D003342:Corpus Striatum / Q000033:anatomy & histology; D005399:Fishes / Q000033:anatomy & histology*; D009833:Olfactory Pathways / Q000033:anatomy & histology*; D012754:Sharks / Q000033:anatomy & histology*; D013045:Species Specificity; D013687:Telencephalon / Q000033:anatomy & histology