Definition of "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.

1997, Ray C. Henrikson, Gordon I. Kaye, Joseph E. Mazurkiewicz, “Bone”, in Histology (National Medical Series for Independent Study), Baltimore, Md.: Lippincott Williams & Wilkins, page 131

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

2011, Corey M. Maggiano, “Making the Mold: A Microstructural Perspective on Bone Modeling during Growth and Mechanical Adaptation”, in Christian Crowder, Sam Stout, editors, Bone Histology: An Anthropological Perspective, Boca Raton, Fla.: CRC Press, page 52