Page 269 - Atlas of Histology with Functional Correlations

illustration, bone is stained dark red. Osteoprogenitor cells from the inner

periosteum (6) continue to differentiate into osteoblasts, deposit osteoid and
bone (8) around the remaining plates of calcified cartilage (15), and form the
periosteal bone collar (7).

Formation of new periosteal bone (7) keeps pace with the formation of new
endochondral bone. The bone collar (7) increases in thickness and compactness

as development proceeds. The thickest portion of the bone collar (7) is in the
central part of the developing bone called the diaphysis. The primary center of
ossification is located in the diaphysis, where the initial periosteal bone collar (7)
is formed.

Red bone marrow (16) fills the cavity of newly formed bone with
hematopoietic (blood forming) cells. Fine reticular connective tissue fibers in the
bone marrow (16) are obscured by masses of developing erythrocytes,
granulocytes, megakaryocytes (12), bony spicules (11, 22), numerous blood
sinusoids (20), capillaries, and blood vessels.

Surrounding the shaft of the developing bone are the soft tissues. The
epidermis (18) of skin is lined by stratified squamous epithelium. Below the
epidermis (18) is the subcutaneous connective tissue of the dermis (19), in
which are seen in hair follicles (9), blood vessels (10), adipose cells (21), and

sweat glands (23).

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