Notes on the brain and encephalization quotient of two sperm whales with a synthesis of the literature and indications of a new method of extraction

The sperm whale (Physeter macrocephalus, Linnaeus 1758) possesses the largest brain that ever existed. Relatively few authors have dealt with it and the available descriptions are heterogeneous, with only few data about brain weight or gross anatomy. In fact the central nervous system of large cetaceans is quite difficult to obtain, given the huge body size and the low frequency of strandings of recently dead individuals. Furthermore, since the skull of the sperm whale underwent an extreme transformation for the accommodation of the spermaceti organ, the cranial cavity is surrounded by thick layers of bone and thus difficult to reach under field conditions. We recently had the chance to extract the brain from two stranded sperm whales whose bodies were in good condition. In the present note we describe the main macroscopic characteristics of the sperm whale brain, including its weight and Encephalization Quotient, review the available literature, and describe a possible new approach to the removal and preservation of the organ under field conditions.