Spatial relationships between the morphologies and innervations of the scalene and anterior vertebral muscles

The prevertebral muscles are innervated by the cervical ventral rami. However, little information is available on the spatial relationships between the muscles and the supplying branches. This gross anatomical study investigated the prevertebral muscles and the nerves in 26 cadavers to elucidate their spatial interrelationships and the nerve pathways to each muscle. These muscles were characterized by the variations in the vertebral attachments. The scalenus medius was divisible into the dorsal and ventral parts. The scaleni anterior and medius attached to both the anterior and posterior tubercles of the cervical transverse processes. The oblique fibers arising from the transverse processes joined the vertical part of the longus colli. The rectus capitis anterior, the longus capitis and the scalene anterior and minimus were innervated by the ventromedial branches of the cervical ventral rami, and the branches passed between the origins of the proximal muscles to supply the longus colli. The rectus capitis lateralis and the scalenus medius were innervated by their dorsolateral branches, and the branches pierced the medius to the scalenus posterior. The roots of the brachial plexus passed between the scalenus anterior and the ventral part of the medius. The penetrations by the upper roots and the interconnecting fibers passing between the roots were found in the muscle bundles arising from the fourth or fifth cervical vertebrae. Their anomalies are the possible causes of the cervical-brachial disorders, and the knowledge of the innervation and the variations in this study seems to be useful for surgical and non-surgical treatments.