Abstract
1. A case of spontaneous fracture of a first rib is described.
2. Its evolution from a previously intact rib through the stage of a "linear" crack to pseudarthrosis has been traced.
3. An older pseudarthrosis was present on the opposite side.
4. Alderson's observation is confirmedâthat the breach in the rib is acquired. There is no need to suppose a developmental anomaly of ossification, even in a bilateral case.