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10. The secondary blood supply to the latissimus dorsi, consisting of a vertical row of paravertebral perforating vascular pedicles from the lumbar aorta, is encountered beneath the latissimus dorsi muscle in the most posterior aspect of the dissection. These pedicles must be divided to allow harvesting of the maximum amount of muscle.
11. The external oblique muscle anteriorly and the paraspinous muscles posteriorly are encountered in the most inferior portion of the dissection of the latissimus. These muscles are intimately adherent to the caudal portion of the latissimus and lumbodorsal fascia and must be separated from it.
Operative Sequence
PLATE XIX-1. Anatomy
 A. The key anatomic structures in the latissimus dissection are shown. The posterior axillary fold is made up of the latissimus muscle as it approaches the humerus on its medial surface, joined by the teres major arising from the scapula. The axillary artery in the apex of the axilla is shown giving off the subscapular artery from the third part of the axillary artery as it comes out from under the pectoralis minor. The subscapular artery soon sends off a large dorsal branch of the circumflex scapular artery. It proceeds down on the surface of the subscapularis muscle to reach the undersurface of the latissimus dorsi, where it enters the fibers of the muscle accompanied by the thoracodorsal nerve. The continuation of this artery provides the blood supply to the lower portion of the serratus anterior, or slips 6, 7, 8 and 9. A rather inconsistent large branch may come off the subscapular and go directly to the skin to supply a purer cutaneous flap.15
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 B. For most dissections of the latissimus dorsi, the patient is placed in the full lateral position stabilized with a large "bean-bag" so that the posterior midline can be easily reached. The entire arm and shoulder are included in the preparation and exposure to permit manipulation of the arm for the axillary dissection and to prevent unusual traction of all pressure points during the operation. Fibers of the latissimus can be seen fanning out transversely across the angles of the scapula to reach the lumbodorsal fascia in the midline. Some fibers insert into the scapula and can be confused with the teres major. Large perforators enter the base of the muscle in the intercostal spaces. The anterior fibers are directed at almost 90 degrees to the upper fibers and descend to the iliac crest. The circumflex scapular vessels go through the triangular space to reach the dorsal and medial surfaces of the scapula.
PLATE XIX-2
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