A forgotten organ: Comparative anatomy of the clitoris in muroid rodents

Despite the extensive study of the penis and associated male glands, knowledge of clitoral anatomy remains limited—even in highly diverse groups like muroid rodents. This reflects a broader lack of attention to the female genital system, particularly in descriptive anatomical studies. Here, we present the first descriptive and comparative analysis of the clitoris in muroid rodents, including a terminological proposal and general anatomical overview, with emphasis on the Sigmodontinae subfamily, the most diverse clade within Cricetidae. We examined the macroscopic clitoral anatomy in representatives of the tribes Akodontini, Cricetini, Ichthyomyini, Murini, Neomicroxini, Oryzomyini, Rattini, and Sigmodontini—encompassing all major clades of Sigmodontinae (Ichthyomyini, Oryzomyalia, and Sigmodontini) as well as key outgroups. The clitoris in muroid rodents exhibits a complex morphology, with diverse combinations of tubercles, dimples, clefts, and depressions. Notable variation was observed in the position and length of lateral mounds, urethral processes, and the dorsal papilla. Sigmodontinae species possess a smooth tissue band absent in Muridae. Another distinguishing feature is the presence of notches on the ridge of clitoris, seen in Muridae but absent in Sigmodontinae. Within Cricetidae, the dorsal papilla and tubercles are present in Cricetini, Oryzomyini, and Sigmodontini, whereas Ichthyomyini lacks the papilla and exhibits dimples. Lateral mounds align parallel to the medial mound in Sigmodontini and Oryzomyini, but are positioned opposite the medial mound in Ichthyomyini. Additionally, an os clitoris was identified in Akodon, Scapteromys, and Neomicroxus, but was absent in other tribes. These morphological traits reveal distinct anatomical patterns with potential phylogenetic significance. Far from being simple or uniform, the clitoris in muroid rodents displays substantial and previously overlooked diversity.