The |compact bone| layer features a number of foramina (openings) which allow the nutrient vessel(s) to tunnel through to reach the |marrow| cavity and spongy bone tissue within. Most bones have one main nutrient vessel which, by branching into a web of |arterioles| within the bone, feeds them, though the |femur| has two such nutrient ~blood~ vessels. The bone has one ~foramen~ for the entrance of each nutrient vessel, and foramina at the extremities for the produced ~blood~ to pass out of the bone.
