A Case of M. Supracostalis Anterior

Kang, Ho Suck; Cho, Byung Pil

Abstract

M. supracostalis anterior is a rare varlation which occurs on the external aspect of the upper thoracic wall. This thin, short-like musc1e lies deep to the pectoralis major and minor muscles, and extends longitudinally over the upper four or five ribs. It is known that the muscle usually occurs bilaterally but sometimes unilaterally. In the present report, a case of unilateral (right) M.supracostalis anterior, observed in a 58-year-old man cadaver, is described. Because the muscle had not been reported in Korea, morphological characteristics and nerve innervation of the muscle were investigated. 1. M. supracostalis anterior, observed only on the right side, extended longitudinally from the first rib to the fourth rib deep to the pectoralis minor. 2. The suprarostalis anterior arose from the antero-inferior surface below the groove for subclavian vein of the first rib. After arising from the first rib, the smaller, more media part of the muscle inserted into the upper border of the fourth rib and the larger, more lateral part inserted into the upper border of the fourth rib. 3. The length of the musce is 9.9cm, and the width is 0.8cm at its origin, 1.7cm at the upper border of the third rib and 2.4cm at the upper border of the fourth rib. 4. It was confirmed, under stereomicroscope, that the muscle was innervated by the terminal branches of the nerve to the first external intercostal muscle deriving from Thl and Th2. Blood supply of the M. supracostalis anterior was provided mainly by the lateral thoracic artery arising from the axillary artery.