The narrow, slit-like (cleft-like) opening between two bones is called a fissure. It's a bone marking that forms a passageway for blood vessels and nerves.
Markings are bone features that serve as:
• Sites of attachment for muscles, ligaments, and tendons
• Joint surfaces
• Conduits for blood vessels and nerves
Check out some of the terms used to describe bone markings or features on bones at Deltacollege.edu.
As you age, your bones become thinner and lose their density. Over time, you become more prone to injury. Fortunately, you can take steps to halt the “thinning” of your bones, called osteopenia, and prevent osteoporosis. Here are some tips on how to halt the thinning of your bones as you age shared by Clevelandclinic.org.