The Structure and Growth of Bone

Internally a bone is a latticed structure of hard, calcified struts, called trabeculae, filled in its core with bone marrow. Bone is nourished by its own blood supply that enters each bone through a nutrient membrane, or foramen.

Bones grow continuously during kittenhood. The skull begins as separate bones, to permit birth, then fuses along suture lines. In some young kittens a small soft spot can be felt on top of the skull; this disappears rapidly

The long bones of the limbs and rib cage begin as hollow tubes of cartilage, and calcify in infancy, replacing cartilage with bone. The outside of the tube, the periosteum, produces new cells, thickening the bone. Inside, the old bone is constantly remodeled to maintain uniform thickness.

Bones lengthen by constant production of new bone at the growth plates, or epiphyses, at their ends, which are fed by a rich supply of tiny arteries.

The growth plates are prone to injury during skeletal development, and both growth hormones and sex hormones influence growth. Curiously, sex hormones inhibit activity; cats neutered very early tend to grow slightly longer leg bones.

If a bone breaks, cells on the periosteum are activated, producing new bone to bridge the gap. Usually, too much new bone is made, but the excess is gradually remodeled from the inside.