A cross section of a human bone reveals that the strong material is on the outside and the inside is used as a factory for blood cells of various kinds.
Sehemu ya mfupa wa binadamu iliyo fanyiwa upasuaji inaonyesha kwamba vifaa vigumu viko nje na ndani hutumika kama kiwanda kwa ajili ya seli za damu ya aina mbalimbali.