Question

what do arrows a and b point to
this is the structure of a long bone with arrow a pointing to a portion that forms the long axis of the bone and arrow b pointing to white double - layered membrane.

Explanation:

The diaphysis is the shaft of a long - bone which forms the long axis. The periosteum is a white double - layered membrane that covers the bone. Arrow A points to the diaphysis and arrow B points to the periosteum.

Answer:

diaphysis, periosteum