The anatomy of the triceps brachii muscle revisited, with new insights into the proximal radial nerve distribution in the goat

The aims of this study were to reexamine the anatomy of the triceps brachii muscle, with particular emphasis on its accessory head(s), and to demonstrate the branching patterns of the radial nerve to the caudal brachial muscles and the brachialis muscle in the goat. Twenty forelimbs from 10 adult domestic goats (8 females and 2 males) were dissected. In all specimens, a previously undescribed humeral attachment site of the long head of the triceps brachii was observed via a narrow, transparent aponeurosis just proximal to the teres major tuberosity. The accessory head originated through fleshy fibers as a continuation of the proximal origin of the medial head from the caudomedial aspect of the humeral neck, while the medial head arose via an aponeurosis from the medial surface of the middle third of the humerus. Several variations in the triceps brachii heads were also noted. At the flexor surface of the shoulder joint, the radial nerve gave off a bundle of muscular branches to the elbow extensor muscles. Except for the branches to the long head and tensor fasciae antebrachii, the primary branches to the lateral head and anconeus, together with the continuation of the radial nerve, passed laterally between the medial and accessory heads. The medial and accessory heads received most of their innervation through several secondary branches (up to four) originating from the primary branches to the lateral head and anconeus. Additionally, in 8 (40%) of the 20 antimeres, a fine single branch arose bilaterally from the radial nerve to the distal brachialis muscle. This study provides a foundation for further biomedical and evolutionary investigations.