Day 14: The Skeleton
The Growth of Bone
This image is a light microscopic view of the
humerus (upper arm bone) of a three and a half month
old dog. The purple line across the section is the
cartilaginous growth plate. The growth plate remains
active through puberty and is responsible for
lengthening the long bone. New cartilage forms at the
top of the growth plate while new bone forms on older
cartilage fragments at the bottom of the plate.
Spongy bone has formed where cartilage used to be in
the primary and secondary centers of ossification.
Cartilage remains on the head of the humerus to form a
smooth gliding surface for the shoulder joint.
Image and text by Jo Ann Eurell.
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