Answer:
Endosteum
Explanation:
The hollow region in diaphysis is known as medullary cavity which is filled with the yellow marrow.
<u>The endosteum is the thin vascular membrane of the connective tissue which lines up inner surface of bony tissue which forms medullary cavity of the long bones.</u>
Endosteal surface is reabsorbed usually during the long periods of malnutrition and thus resulting in the less cortical thickness.
