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| | * Stallion | | * Stallion |
| − | * Increases in diameter during erection and [[Reproductive_Behaviour_-_Pre-copulatory_Behaviour_-_Anatomy_%26_Physiology#Penile_Protrusion|protrusion]]. | + | * Increases in diameter during erection. |
| | + | * '''Retractor penis muscle''' still relaxes during erection, but '''no sigmoid flexure'''. |
| | + | * Engorgement with blood plays a significant role in the highly vascular penis. |