In the left upper limb of an adult male cadaver a triangular muscular slip, 3.5 cm long and 2.5 cm wide, arose from the lower border of latissimus dorsi just proximal to its tendon of insertion. It was inserted by a slender 6 cm long tendon mainly into the coracoid process of the scapula. Three short fibrous strands radiated from this slender tendon to gain attachments to pectoralis minor and the common tendon of origin of the short head of biceps brachii and coracobrachialis. In addition 2 flat tendinous bands attached the margin of this muscular slip to teres major. The thoracodorsal nerve entered the main bulk of latissimus dorsi close to the muscular slip but did not supply a separate branch to the latter. This is an axillary arch muscle in an unusually medial location.
The anatomical orientation of structures in the axilla has not been well studied, although it is essential for a neat and safe dissection. The objective of this study was to determine the relations between neurovascular structures in the axilla as they were encountered during axillary lymph node dissection (ALND) for breast cancer.
The latissimus dorsi is a muscle of the back which forms the posterior fold of the axilla and its tendon twists to insert into the floor of the intertubercular sulcus of the humerus. Occasionally, the muscle has a muscular slip which crosses the axilla to insert into the pectoralis major. This muscular slip is often termed as "axillary arch." In the present study, we report bilateral axillary arch detected in a 45-year-old male cadaver. The average vertical length of the axillary arch measured 7 cm. The average maximum width of the uppermost, middle and lower part of the arch measured 2, 3.5 and 3.2 cm, respectively. The presence of the axillary arch is an uncommon finding in humans, considering the fact that it is solely found in the animals who prefer to hang on the trees. A histological study of the axillary arch was also performed and it showed skeletal muscle fibres which was uniformly arranged. The presence of the axillary arch may assist in the adduction of the shoulder. It may also compress the axillary vessels and nerves thereby causing resultant symptoms. Prior anatomical knowledge of the presence of axillary arch may be helpful for surgeons performing radical dissection of the axillary lymph nodes and ligation of axillary vessels, clinicians diagnosing abduction syndromes and interventional radiologists interpreting axillary mass in day to day clinical practice.