Illustrated Encyclopedia of Human Anatomic Variation: Opus III: Nervous System: Plexuses
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
The cervical plexus consists of three loops. A large part of the anterior primary division of the first cervical nerve is given to the hypoglossal or cervical loop. The remainder contributes to the cervical plexus thus forming the first loop. From the first loop of the plexus, two branches of the first cervical nerve usually enter the sheath of the hypoglossal nerve (or may instead enter the sheath of the vagus nerve) and descend with it to contribute to the hypoglossal or cervical loop. The first cervical nerve leaves the hypoglossal (or vagus) as the descendens cervicalis or hypoglossi at the level of the occipital artery and later joins the communicans cervicalis, which arises from the second and third cervical nerves, completing the hypoglossal or cervical loop. The location of this loop is variable. It is usually found between the sheaths of the sternocleidomastoid and carotid artery superficial to the internal jugular vein, but may instead be located between the carotid artery and the internal jugular or, rarely, dorsal to both artery and vein. It may be long, terminating below the level of the thyroid cartilage, or short, terminating at the level of the hyoid bone. The descendens hypoglossi (or cervicalis) runs distally on the sheaths of the great vessels or may be located within one of these sheaths.
The second cervical nerve contributes to the first and second loop of the cervical plexus. The third cervical unites with the second and fourth cervical to complete the lower loops of the plexus.
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