The nuclear fibrous lamina of alveolar bone cells

The nuclear fibrous lamina, a structure of unknown composition and function, is described in alveolar bone cells of squirrel monkeys. Osteoblasts, osteocytes, and osteoprogenitor cells contain nuclear envelopes with prominent fibrous laminas measuring up to 800° A. in width, while osteoclasts have nuclei with poorly developed laminas. The fibrous lamina is an amorphous or fine‐textures, moderaly electron dense layer directly applied on its external surface to the inner nuclear membrane. Its interior surface is bordered by beads of heterochromatin. At nuclear pore sites the lamina is either absent or markedly attenuated.