This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Posteriorly, the artery lies on the first intercostal space and muscle, the second and pare of the third serrations of the serratus anterior, the posterior thoracic nerve (or external respiratory of Bell), and the internal anterior thoracic nerve to the pectoralis minor and major.
To the inner side of the artery and somewhat anteriorly is the axillary vein; between the two runs the internal anterior thoracic nerve. As the artery and vein ascend they become separated, the artery to pass behind and the vein in front of the scalenus anterior muscle.
To the outer side and above the artery lie the cords of the brachial plexus.
In front of the artery are the skin and superficial fascia, the edge of the pectoralis major muscle and fascia covering it, the costocoracoid membrane pierced by the acromiothoracic artery, cephalic vein, and external anterior thoracic nerve, which goes to supply the pectoralis major muscle.
The artery lies deep in the infraclavicular triangle, between the pectoralis major and deltoid muscles. It can be approached by either a transverse or a longitudinal incision. If the former is used it should be made through the skin only, immediately below the clavicle, reaching from just outside the sternoclavicular joint to the coracoid process.
The pectoralis major is detached from the clavicle and pushed downward, it arises from its inner half. This exposes the costocoracoid membrane. At the outer angle of the wound the cephalic vein and acromiothoracic artery are to be found.
The deltoid muscle is to be detached or pushed outward to expose the coracoid process, this being recognized, the costocoracoid membrane is to be opened to its inner side, between it and the cephalic vein. The acromiothoracic artery if isolated will lead to the artery, while the cephalic vein goes direct to the subclavian vein. The vein and costocoracoid membrane are closely united and great care is necessary to avoid wounding the former in opening the latter. The cords of the brachial plexus are to the outer side of the artery and care is to be exercised not to mistake one of them for the artery. As the vein is the most dangerous structure, it is to be displaced inward and the aneurism needle passed between it and the artery from within outward.
As the external anterior thoracic nerve is a nerve of motion supplying the pectoralis major muscle, if it is seen it should be avoided and not injured.
If it is desired to use a longitudinal instead of transverse incision, it should commence just outside the middle of the clavicle and follow the groove between the deltoid and pectoralis major muscles downward for 10 cm. (6 in.). Great care is then necessary to avoid wounding the cephalic vein and acromiothoracic artery, which lie in this groove.
If sufficient exposure is not given by a single straight incision it can be supplemented by one detaching the pectoralis major from the clavicle.