Origin and composition of the brachial plexus in the alpaca (Vicugna pacos )

Alpacas (Vicugna pacos), members of the family Camelidae, are gaining popularity in Europe and worldwide. This study describes the origin and composition of the brachial plexus in alpacas and compares them with those of selected mammals. Six alpacas, aged one day to 16 years, were examined. In five animals, the plexus was formed by the ventral branches of C7, C8, and T1; in one specimen, T2 also contributed. After passing through the scalenus muscles - with C7 traversing separately from the caudal roots (C8, T1) - the roots continued as trunks toward the forelimb. Fibre exchange resulted in the formation of two cords. Nerves to the shoulder girdle muscles, except for the caudal pectoral nerve, contained only C8 fibre bundles. The suprascapular, subscapular, and axillary nerves arose from the cranial cord (C7, C8), which continued distally as the radial nerve (C8, T1). The caudal cord first gave rise to the cranial pectoral nerve (C8), followed by the caudal pectoral nerve (C8, T1) and the ulnar nerve (C8, T1), and then continued as the median nerve. The musculocutaneous nerve (C7, C8) originated at the trunk level, coursed caudally, and joined the median nerve in the ansa axillaris, resulting in the median nerve containing fibre bundles from all three spinal nerves. The reduced number of contributing spinal nerves and the distinctive arrangement of the plexus may be related to the elongated cervical vertebrae of alpacas. These findings support clinical applications, particularly in forelimb surgery and nerve block techniques, and provide comparative insights into morphological adaptation of the brachial plexus among mammals.