and macaques; however, only in macaques does keratinization of the epithelium occur during the follicular phase. The vaginal pH of macaques also differs, with near-neutral to slightly alkaline median values and is widely variable, which may be due to its lack of lactobacilli in the vaginal flora. This is one reason why, although macaques are used for studying HIV transmission and testing microbicides, animal models are not often used in the study of sexually transmitted infections, such as trichomoniasis. Another is that such conditions' causes are inextricably bound to humans' genetic makeup, making results from other species difficult to apply to humans. See also Artificial vagina Gynoecium Smegma Supravaginal portion of cervix Uterine inversion Vaginal dilator Vaginal photoplethysmograph References External links Vagina, Anatomical Atlases, an Anatomical Digital Library (2018) Human female reproductive system Mammal female reproductive system Women and sexuality Women's health Anatomy Gynaecology