Bilateral extensor medii proprius with split tendon of extensor indicis proprius, a rare anatomical variant

Vol. 54 No. 3 Suppl., 2013
This supplement was not sponsored by Outside Organizations.


Jing Li, Zhen Feng Ren

The extensor medii proprius (EMP) is anomalous extensor muscle of the hand. During the routine dissection of a 78-year-old Chinese male cadaver, bilateral EMP and extensor indicis proprius (EIP) were observed in the upper limbs. The EMP originated from the distal third of the ulna and its tendon was inserted into the dorsal aponeurosis of the middle finger on both hands. The tendon of EIP was split into two slips on the dorsum of hand and inserted to the radial and ulnar side of the extensor digitorium communis (EDC)-index, respectively. Awareness of such anatomical variations in the extensor compartment of the forearm could help in the identification and repair of these structures.

Corresponding author: Jing Li; e-mail:

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Ceren Gunenc Beser, Burcu Ercakmak, S. Tunali, Ruhgun Basar

Variations on the neuromuscular structures of the upper limb reflect the complex development of that region. Many of them may be important during surgical and/or diagnostic procedures; however, some of them are of academic interest. Here we report a case of six neuromuscular variations in a single upper limb. During routine educational dissection for the undergraduate medical students at the Department of Anatomy, Faculty of Medicine, Hacettepe University, Ankara, Turkey, we came across six variations on the left upper limb of a 43-year-old well-built male cadaver. We conformed to the steps described in Grant's Dissector during the dissection, and photographed the case with a Nikon Coolpix camera. The biceps brachii showed an accessory head that originated from the tendon of pectoralis major, ran downwards superficial to the long head and joined the distal 1/3 of the muscle mass. A thin muscle band accompanying the lateral side of the pectoralis major was identified as pectoralis quartus. It was originated from the sixth rib and inserted to the coracoid process. The coracobrachialis was double-headed having a common origin from the coracoid process, separating into two after a short course and joining again at the middle level of the arm. Musculocutaneous nerve did not pierce the coracobrachialis. Instead, it ran beneath the two bellies of the muscle. The lateral cord of the brachial plexus passed between the two bellies of coracobrachialis; then divided into musculocutaneous nerve and the lateral root of the median nerve at a lower level than usual. The right upper limb showed no variations. The variations described here maybe commonly encountered individually; however, the combination of six of them in a single arm is previously unreported.

Corresponding author: Selcuk Tunali, MD, PhD; e-mail:,

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