Innervation of the levator scapulae, the serratus anterior, and the rhomboideus in crab-eating macaques and its morphological significance.

The origin, course and distribution of the nerves supplying the levator scapulae, the serratus anterior, and the rhomboideus were carefully examined in four body-halves of crab-eating macaques. The levator scapulae arises from all the cervical vertebrae and is continuous with the serratus anterior, which arises from the upper ten ribs. The rhomboideus originates not only from the dorsal midline but also from the occipital bone. 6 segmental nerves from C3 to C8 innervate the 3 muscles: C3, C4, C5, and C6 innervate the levator scapulae; C6, C7, and C8 the serratus anterior; and C3, C4, C5, and C6 the rhomboideus. Each segmental nerve of supply originates as one or 2 branches from the dorsal surface of the corresponding root of the cervico-brachial plexus and runs dorso-caudally to enter the muscles. After supplying them, 6 or 7 branches pierce the levator scapulae and serratus anterior to reach the deep surface of the rhomboideus which they innervate. The upper segmental nerve tends to be distributed to the upper part of the muscle it innervates, while the lower segmental nerve is distributed to the lower part. According to the relationships between nerves and muscles, these 3 muscles may be regarded as the most medial of the dorsal musculature which is connected to the pectoral girdle and limb, as they are in man. It may surmised that the occipital portion of the rhomboideus and the caudal portion of the levator scapulae in crab-eating macapues correspond to the cranial portions of the levator scapulae and serratus anterior, respectively, in man.