The medial supraclavicular nerves arise from the common trunk of the supraclavicular nerve deep to platysma and the deep cervical fascia.  It passes infero-medially across the external jugular vein and clavicular and sternal heads of the sternocleidomastoid.

Supply
The medial branch supplies the skin over the manubrium as far as the midline, as well as the sternoclavicular joint.