Anatomical Study of the Brachial Plexus in the Common Marmoset (Callithrix Jacchus).

To elucidate the forelimb phylogeny of primates, anatomical analysis of the brachial plexus in platyrrhines is beneficial. In the present study, six brachial plexuses and the surrounding arteries of four common marmosets were dissected. In five specimens, the brachial plexus consisted of five ventral rami from the fifth cervical nerve (C5) to the first thoracic nerve (T1). In one specimen, the ventral ramus of the fourth cervical nerve joined with the brachial plexus. In five specimens, the upper trunk was composed of C5 and the sixth cervical nerve (C6). In one specimen, the ventral division of C6 merged with the ventral branch of the middle trunk to constitute the lateral cord. The seventh cervical nerve constituted the middle trunk, and the eighth cervical nerve and T1 formed the lower trunk in all specimens. The lateral cord gave rise to the musculocutaneous nerve, and the remaining component merged with the medial cord. The confluence of the lateral and medial cords immediately bifurcated into the median and ulnar nerves. These branching patterns of the musculocutaneous, median, and ulnar nerves were consistent and similar to the human counterparts. In the dorsal division, the single posterior cord as observed in the human brachial plexus was not observed. The axillary artery did not pass between the medial and lateral roots of the median nerve, and the axillary artery bifurcated into the brachial artery and the superficial brachial artery. Anat Rec, 300:1299-1306, 2017. © 2017 Wiley Periodicals, Inc.