I enjoy gazing admiringly at the anal orifices of Paris Dahl, Zuzana Zeleznovova, and Holly Rydem -- all 3 of these beauties also have interesting perinea (the bridge between their assholes and their pearlescent pink pussies).
So far as I can determine, the female perineum should be smooth. The male perineum may have a visible, narrow ridge on the midline called the perineal raphe. While that raphe is an anatomical reference point for both sexes, it seems that normally it's externally observable only in males.
The previously-mentioned episiotomy procedure (among other surgical procedures perhaps), possibly trauma from anal sex/insertions, and some medical or embryological conditions might result in something that appears to be a narrow midline ridge in women.
"To investigate intergender differences in muscle cleavage and joining during development of the external anal sphincter (EAS), we examined semiserial sections of 16 fetuses between 15 and 30 weeks of gestation (6 males and 10 females). The subcutaneous part of the EAS (EASsc) developed along the male perineal raphe and extended posteriorly. Thus, the male EAS was characterized by anterior protrusion of the subcutaneous muscle, in contrast to the almost circular female EAS. In both genders, the bulbospongiosus anlage (or the levator ani anlage) issued muscle fibers to form the superficial (or deep) part of the EAS. The EASsc communicated with the superficial part in males, whereas the female bulbospongiosus tended to communicate with the levator ani rather than the EAS. In both genders, the longitudinal muscle bundle(s) of the anorectum contributed to perineal body formation. However, the male perineal body also had a thick fascia between the rhabdosphincter and the levator. The bulbospongiosus seems to play a critical role in forming the EAS. A strict intergender difference in subcutaneous muscle development is evident along the perineal raphe, as the raphe is not
evident in females. These results help to explain variations in the EAS, including anal malformations."
Okajimas Folia Anatomica Japonica. 2010 Aug; 87(2): 49-58. [Japanese source]
https://www.ncbi.nlm.nih.gov/pubmed/20882767
"Pathogenesis of perineal groove remains unclear. However, embryological mechanisms have been proposed as follows: (1) a relic of the open cloacal duct, (2) midline fusion failure of medial genital folds between the perineal raphe and the vestibule, and (3) urorectal septum developmental defect during cloacal embryological stages at 5th to 8th week of GA [gestational age]. Given that the perineal groove anomaly was also reported in one male infant, this congenital anomaly can be derived during the embryological development stage of external genitalia. External genitalia of both sexes are developed from the genital tubercle, genital folds, and labioscrotal folds. Therefore, failure of labioscrotal folds fusion to form perineal raphe will cause perineal groove to occur."
American Journal of Perinatology Reports. 2016 Mar; 6(1): e30-e32.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4737640/
Perineal Groove: A Rare Congenital Midline Defect of Perineum