Fibroblasts create compartments in the extracellular space where collagen polymerizes into fibrils and fibrils associate into bundles.

Morphogenesis in the animal kingdom is closely coupled with the intracellular synthesis and the extracellular deposition of collagen. These morphogenetically important events involve multiple steps which begin in compartments inside the cell and continue in compartments outside the cell. The movement of matrix components from the intracellular compartments to the extracellular compartments is a functional continuum. Studies of embryonic chick tendon and cornea fibroblasts with the high-voltage (1000 kV) transmission electron microscope have provided the beginnings of an understanding of how this functional continuum is related to the structural compartments which the cells create. This series of compartments, both inside and outside the cell, is involved in collagen fibrillogenesis, collagen fibril bundle formation, and tissue morphogenesis.