Structure and relationship of the mammillary gore to membrane fibres and initial calcification of the avian Egg Shell1

The interior of the mammillary knob is shown to be composed of: (1) outer shell membrane fibres that penetrate the basal portion of the knob and become associated with (2) The mammillary core, and (3) the bulk calcification of the main knob. 2. The mammillary knob consists of radial crystals which are arranged in a hemisphere on the outer shell membrane fibres, and are composed of a central zone which is a homogeneous solid, crystalline in nature, and an outer heterogeneous vesiculated zone. 3. The walls of the mammillary knob are continuous with the base and sides of the mammillary core radial crystals; the dorso‐central zone of the core crystals are exposed to a cavity that communicates with the upper zones of the mammillary knob and palisade layer via the central channel. The dorsal surface of the core cavity is formed by a layer of unorganised crystals of the mammillary knob proper. 4. Initial calcification of the knob begins at the base and sides of the mammillary core and expands over the organic core as the walls of the knob thicken during subsequent calcification. Incomplete fusion of the central expansions from peripheral knob areas results in the central channel.