Periosteum

Periosteum and endosteum are connective tissue sheaths of bone. […] The periosteum is a layer of connective tissue covering the external surface of a bone. The periosteum may be divided into two components: / a. An outer fibrous layer consists of dense irregular connective tissue. / b. An inner cellular layer consists of osteoprogenitor (osteogenic) cells.

The periosteum is constrained and interrupted by tendons, ligaments, and fibrocartilage, whereas the endosteum is awash with hematopoitic bone marrow[…].