Fine structure of bone as seen on fracture and cleavage planes by electron microscopy

Surface replicas were made of fracture surfaces and cleavage planes of specimens of human femoral cortex. Examination by electron microscopy indicated no consistent differences in submicroscopic structure when fractures were produced by compression, tension, torsion or bending. Small apertures, ranging from 200 to 1,500 Å in diameter, permeated the extra‐canalicular bone. Higher magnifications indicated that the majority of apertures were truncated canals which were enclosed by collagen fibrils with axes aligned longitudinally with the direction of the canals. When canaliculi were observed in cross section, fibrils were observed to radiate at right angles from the canalicular axis for approximately 1 μ. No differences in submicroscopic structure were observed between adult bone and that of a 12‐year old child.