Clarification on the dorsal scapular and transverse cervical aa.

Usually, the Dorsal scapular artery comes off of the subclavian a. on its own. Approximately 1/3 of the time, however, it comes off of the thyrocervical trunk as a deep branch of the transverse cervical a. [Therefore, the transverse cervical a. only exists if the dorsal scapular and superficial cervical aa. are branches of a common artery (which itself arises from the thyrocervical trunk); this 'common' artery is called the transverse cervical a. If the dorsal scapular a. arises directly from the subclavian a., there is no transverse cervical a. - only a superficial cervical a.!]