Long head of triceps supplied by axillary nerve

Introduction The axillary nerve comes from the posterior cord of the brachial plexus at the level of the axilla and carries nerve fibers from C5 and C6. The axillary nerve travels through the quadrangular space with the posterior circumflex humeral vessels, and divides into anterior and posterior branches. It supplies deltoid and teres minor. It carries sensory information from the shoulder joint, as well as the skin covering the inferior region of the deltoid muscle – the “regimental badge” area [1]. The radial nerve (C5–T1) is the largest branch of brachial plexus and is the continuation of the posterior cord. It is a nerve of extensor compartments of the arm and forearm. It passes through lower triangular space and spiral groove and pierces the intermuscular septum of arm, to enter into front of the arm and finally divides into superficial and deep branches in front of the elbow joint. It supplies all the 3 heads of triceps brachii muscle by separate branches to each of the head [1]. Most of the anatomy textbooks say that the motor branch of the long head of the triceps brachii arises from the radial nerve, but some cadaveric studies have shown that the triceps is innervated by the axillary nerve. Awareness of such variations is important for clinicians and surgeons. Case Report During routine dissection study and teaching to undergraduate students in Anatomy department, MSRMC, Bangalore, We found bilateral variation in the innervation to long head of triceps in an adult male cadaver aged 60–70 years. The motor branch to the long head of the triceps was arising from the axillary nerve bilaterally, instead of its usual origin from radial nerve. The axillary nerve after passing through the quadrangular space instead of bifurcating, was trifurcating into the anterior branch, the posterior branch and a branch to the long head of triceps. The other branches of both the nerves were as usual in origin and course bilaterally (Figure1).