Brazilian Boidae hemipenis morphology: Macroscopic and histological aspects

Four genera of the Boidae family are found in Brazil: Eunectes, Corallus, Epicrates, and Boa. Male copulatory organs in snakes are located inside the tail and are called hemipenes. They are double structures in an inverted position that are exposed during copulation. This study describes the macroscopic and histological aspects of hemipenes in Boidae snakes. One Boa constrictor, three Epicrates cenchria, one Corallus hortulanus hemipenes, and one fragment of the muscular retractor penis magnus (m. retractor penis magnus) from Eunectes murinus were included in this study. The structures were evaluated macroscopically and photo-documented using a stereo microscope. Tissue fragments were included in glycol methacrylate plastic resin, cut into 3-μm-thick slices, and stained with 1% toluidine blue for microscopic evaluation. The macroscopic analysis showed that the arrangement and diameter occupied by the m. retractor penis magnus in the hemipenis and the internal and external cavernous bodies differ between species. The histological analysis showed that the hemipenis of B. constrictor, E. cenchria, and C. hortulanus has stratified epithelium in the external portion supported by dense connective tissue with blood vessels and muscle tissue. Although the literature reports the presence of skeletal musculature in the hemipenis, striated musculature with a centrally located nucleus in the fibre bundle, typical of cardiac musculature in mammals, was observed in the studied species.