The Supraclavicular Nerves (nn. supraclaviculares; descending branches) arise from the third and fourth cervical nerves; they emerge beneath the posterior border of the Sternocleidomastoideus, and descend in the posterior triangle of the neck beneath the Platysma and deep cervical fascia. Near the clavicle they perforate the fascia and Platysma to become cutaneous, and are arranged, according to their position, into three groups :
- The medial supraclavicular nerves (anterior supraclavicular nerves ; nn. supraclaviculares anteriores; suprasternal nerves) cross obliquely over the external jugular vein and the clavicular and sternal heads of the Sternocleidomastoideus, and supply the skin as far as the middle line. They furnish one or two filaments to the sternoclavicular joint.
- The intermediate supraclavicular nerves (middle supraclavicular nerves ; nn. supraclaviculares medii; supraclavicular nerves) cross the clavicle, and supply the skin over the Pectoralis major and Deltoideus, communicating with the cutaneous branches of the upper intercostal nerves.
The lateral supraclavicular nerves (posterior supraclavicular nerves ; nn. supraclaviculares posteriores; supra-acromial nerves) pass obliquely across the outer surface of the Trapezius and the acromion, and supply the skin of the upper and posterior parts of the shoulder.
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).