Cervical Spine – Upper cervical flexion is produced principally by concentric contraction of the ventral muscles, sternocephalicus, longus capitis and longus colli. Sternocephalicus, aslo known as sternomandibularis, is obvious from a surface view as it forms the ventral border of the jugular groove. Extension is produced by bilateral contraction of the erector spinae and dorsal cervical muscles. Lateral flexion and rotation are produced by cranial and caudal obliqe and straight muscles of the head, assisted by longus colli, splenius, semispinalis and brachiocephalicus. Of these, brachiocephalicus can be seen as the dorsal margin of the jugular groove. Splenius is also fairly superficial at its cranial end and runs caudal to brachiocephalicus.
