The brachial plexus of the Japanese serow (Capricornis crispus)

The brachial plexus of the Japanese serow was macroscopically studied. It was composed of nerves derived from the sixth (C6), seventh (C7) and eighth (C8) cervical nerves and the first (T1) thoracic nerve (98.1%). Rarely, the second T2) thoracic nerve joined it (1.9%). C6 joined C7 and made up the cranial trunk. C8 and T1 (+T2) united to form the caudal trunk. Each trunk split into dorsal and ventral divisions. The dorsal divisions from C6-T1 formed the dorsal cord which gave off the thoracodorsal, axillary and radial nerves. The manner of union of ventral divisions and their divergence was classified into 4 types. Type I was that the ventral cord was formed by cranial and caudal ventral divisions and sprouted the musculocutaneous, median and ulnar nerves. It was found in 67.3%. Type II was that the proximal muscular ramus of the musculocutaneous nerve emerged from the median nerve and the ulnar nerve appeared from the caudal ventral division from C8-T1. It was observed in 19.2%. Type III was that the proximal muscular ramus and ulnar nerve were derived from the cranial and caudal ventral divisions, respectively. It was seen in 11.6%. Type IV was quite different from type I to III. The cranial ventral division from C6-C7 was not observed. The caudal ventral division from C8-T1 alone formed the ventral cord giving off the nerves. It was encountered in one case (1.9%) and probably represented rare variation. These findings indicate that the brachial plexus of the Japanese serow is chiefly similar to that of other ruminants.