[2] It arises by a short, thick tendon from the first rib and its cartilage at their junction, in front of the costoclavicular ligament.

[1] The fleshy fibers proceed obliquely superolaterally, to be inserted into the groove on the under surface of the clavicle.

This arises from the junction of the fifth and sixth cervical nerves, from the superior/upper trunk of the brachial plexus.

Sternoclavicularis[3] from manubrium to clavicle between pectoralis major and coracoclavicular fascia.

This article incorporates text in the public domain from page 438 of the 20th edition of Gray's Anatomy (1918)