Cross-sectional shape of humerus
Head of humerus transitions into the body at the bottom of the greater and lesser tubecles. This is the surgical neck (where most fractures occur). The cross section of the surgical neck is circular, but as it moves toward the condyle of humerus, the cross section becomes flattened. It is similar to the body of a balalaika or the plectrum of a guitar. At the more flattened part, there may be a hole (supratrochlear foramen).