What substance is housed in the medullary cavity, yet absent in the trabeculae?

The substance that  is housed in the medullary cavity, yet absent in the trabeculae would be the yellow bone marrow. The color of yellow marrow is due to the much higher number of fat cells. It  is found in the hollow interior of the diaphyseal portion, or shaft of long bones. Hope this answers the question.

It is very important to stay hydrated. your body needs it for may things for cells, tissues, your organs and etc. water also with your temperature that way you don’t get a headache etc. i bet if you look it up there will be a lot of things you can learn.