This small, rough bump sits on the superointernal border of the horizontally flattened first rib approximately midway between the proximal and distal extremities. This is the insertion point of the anterior scalene muscle.

Scalene comes from Greek word skalenos meaning unequal. This is the term applied to a triangle of unequal sides. Here it refers to the anterior scalene muscle that attaches to this landmark. The scalene muscles were originally thought to be one muscle, but are now known to be three. The seventeenth Century French anatomist, Jean Riolan, thought the three muscles formed a single muscle mass resembling a scalene triangle and named it the scalenus muscle. Tubercle arises from the Latin tuber meaning a lump and the diminutive suffix -cle denoting a small lump.

Tuberculum musculi scaleni anterioris

Tubercule du muscle scalène antérieur