Here's why:

* Cellular Composition: The periosteum contains various types of cells, including osteoblasts (bone-building cells), osteoclasts (bone-resorbing cells), and fibroblasts (which produce collagen fibers). These cells are actively involved in bone growth, repair, and remodeling.

* Blood Supply: The periosteum is highly vascularized, meaning it has a rich blood supply. This allows for the delivery of nutrients and oxygen to the cells and the removal of waste products.

* Metabolic Activity: The periosteum exhibits metabolic activity, meaning it carries out chemical reactions necessary for its functions.

In contrast, non-living tissues lack cells, blood supply, and metabolic activity. The periosteum, with its active cellular components and biological processes, clearly falls under the category of living tissue.