Open main menu Penile spines of a domestic cat Many mammalian species have developed keratinized penile spines along the glans and/or shaft, which may be involved in sexual selection . These spines have been described as being simple, single-pointed structures ( macaques ) or complex with two or three points per spine ( strepsirrhines ). [ 1 ] Penile spine morphology may be related to mating system [ clarification needed ] . Non-human mammals Edit Further information: Spotted hyena § Female genitalia , Fossa (animal) § External genitalia and Cat § Reproduction Felines, especially domestic cats, are well known for having penile spines. Upon withdrawal of a cat's penis , the spines rake the walls of the female's vagina , which may cause ovulation. [ 2 ] [ 3 ] Penile spines in chimpanzees and mice are small surface projections made by the piling up of kera...