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3.39 Intramembranous ossification: bone
of cranium (juvenile dog). Active osteo-
blasts form a layer of cells immediately
adjacent to the surface of ossifying spic-
ules of osteoid. Their cytoplasm is strongly
basophilic and their nuclei are typically
spherical with nucleoli. Goldner’s Masson
trichrome stain (x720).

3.40 Processes involved in endochondral ossification in a long bone (schematic). Refer to text for elaboration
upon the use of the term ‘chondroclast’.

production of non-mineralised bone matrix, the osteo- the ossification process there is marked growth of blood
blasts gradually become walled off and the distance capillaries into the connective tissue. These blood vessels
between them increases. They remain in contact, how- are accompanied by additional mesenchymal connec-
ever, via their cellular processes. The ground substance tive tissue. Through this early vascularisation, the bone
gradually becomes mineralised and osteoblasts transform tissue establishes itself as a metabolically active mineral
into osteocytes. The bone matrix contains predominantly depot. The formation and resorption of the bone is closely
irregularly arranged collagen fibres. At the beginning of regulated by various hormones (Figure 3.30).

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