Anatomical Description of the Main Gyri and Sulci of the Telencephalon of <scp> <i>Alouatta belzebul</i> </scp>

ABSTRACT The Alouatta belzebul is a species of howler monkey, of the Atelidae family and genus Alouatta . It is endemic in Brazil and has a separate geographic distribution, with two populations occurring: in the Amazon and in the Atlantic Forest on the coast of Northeast Brazil. The species is classified as ‘vulnerable’, and this is mainly justified by hunting, fragmentation and loss of habitat in tropical forests. Regarding the anatomy of this species, information is scarce and in some aspects such as the brain are non‐existent. The objective of this study is to describe the macroscopy of the main grooves and turns of the A. belzebul telencephalon correlating with the degree of encephalisation, the absolute and relative measures of the central groove sinuosity and the straight and sinuous measures of the grooves in different primates. As well as, check the anatomy of the nuclei of the base. Ten A. belzebul brains were used, where the gyrations and grooves were dissected. It was found that the brain surface of A. belzebul presented with lisencephalic characteristics, similar to the findings with several other species of non‐human primates and differing from species such as Pan and Homo . In the analysis of the encephalisation index, it was observed that this species is phylogenetically closer to Sapajus and Macaca and more distant than species such as Brachyteles and Callithrix , showing expressive cognition and intelligence. Regarding the slope of the central groove, it was observed that in A. belzebul the upper end is posterior to the lower end, data that approximate with Homo , Papio and Pan and reveal a large frontal lobe when compared to Sapajus libidinosus , showing the maximum brain development in these primates.