The latissimus dorsi muscles, commonly called the "lats," are large, flat muscles located on the back. They stretch from the lower spine and pelvis, across the middle and lower back, and extend up through the armpit to attach to the upper arm bone (humerus). Specifically, they originate from the spinous processes of the lower thoracic and lumbar vertebrae, the thoracolumbar fascia, the iliac crest of the pelvis, and the lower ribs. They then pass through the armpit area to insert on the floor of the intertubercular groove of the humerus near the shoulder

. Anatomically, the lats cover much of the lower and mid back beneath the trapezius muscle and form the posterior border of the armpit together with the pectoralis major muscle at the front of the armpit

. They are the broadest muscles of the back and are responsible for movements such as pulling the arms down, extending and internally rotating the shoulder joint, and assisting in trunk rotation

. In summary, the lats are located on the back, spanning from the lower spine and pelvis up to the upper arm, passing through the armpit region.