Brain organization of sharks, with special reference to archaic species

Using photographic measurements and normal neurohistological preparations, a number of brains of Galeomorph and Squalomorph sharks were studied and compared. The brains are generally more developed in Galeomorph than in Squalomorph sharks. Among the major brain territories in Galeomorph sharks, the nucleus centralis is prominently enlarged, and the corpus cerebelli is much swollen and fissured. In archaic species such as Scapanorhynchus, Heterodontus, and Chlamydoselachus, the cerebral pallium and corpus cerebelli are less developed than those of taxonomically close species. These results were discussed, in relation to taxonomy, phylogeny and ecology.