Accessory Slip of Latissimus Dorsi

While analyzing the axilla of a routine dissection from D'Youville College's Gross Anatomy Lab, an extra slip of muscle was observed to arise from the anterior aspect of the latissimus dorsi muscle and insert into the proximal part of corachobrachialis; an intercostal brachial nerve seen slightly deep to this slip helped to confirm that it was an accessory slip. This accessory slip is commonly referred to as an “axillary arch muscle”, and its existence gives immense clinical and morphological significance. The accessory slip can also be known as “Langer's arch”, which is a tendinous, muscular structure extending from the latissimus dorsi muscle to the trilaminar tendon of pectoralis major on the humerus. According to Gray's Anatomy , the muscle slip varies “from 7 to 10 cm in length, and from 5 to 15 mm in breadth” and “is present in about 7 percent of subjects and may be multiple”; coming “from the latissimus dorsi about the middle of the posterior fold of the axilla in front of the axillary vessels and nerves”, the muscle slip crosses in front of the axillary vessels and nerves to insert – or “join” – the deep surface of the tendon of pectoralis major, corachobrachialis, or fascia superficial to the biceps.1 Understanding the significance and incidence of this accessory slip is a benefit to surgeons, especially those caring for patients with breast surgery or any type of axillary surgery, as it tends to be confused with an enlarged lymph node.Axillary Dissection Small slip of Latissimus Dorsi m. inserting on humerus through corachobrachialis m.Closeup of slip of Latissimus Dorsi m. inserting on humerus through corachobrachialis m.