Latissimus Dorsi Muscle

Actions of Latissimus Dorsi:

• Extension of humerus
• Medial rotation of humerus
• Adduction of humerus

Origin of Latissimus Dorsi:

• Thoracolumbar aponeurosis
• Lower 6 thoracic spinous processes
• Sacrum & iliac crest
• Lower 3 to 4 ribs
• Inferior angle of the scapula

Insertion of Latissimus Dorsi:

• Bicipital groove of the humerus

The Latissimus dorsi is really triangular in shape, flat muscle, that covers the lumbar region as well as the lower half over the thoracic region, as well as is steadily contracted into a slim fasciculus at its insertion into the humerus. It originates by tendinous fibers in the spinous processes from the lower 6 thoracic vertebræ as well as in the posterior layer of the lumbodorsal fascia, by which it's affixed to the spines of the lumbar as well as sacral vertebræ, to the supraspinal ligament, as well as to the posterior aspect of the crest of the ilium. It additionally originates by muscular fibers in the external lip of the crest of the ilium lateral to the margin of the Sacrospinalis, as well as in the three or four lower ribs by fleshy digitations, which are generally interposed between similar processes from the Obliquus abdominis externus. From this extensive origin the fibers pass in various directions, the upper ones horizontally, the middle obliquely upward, as well as the reduce vertically upward, so as to converge as well as form a thick fasciculus, which crosses the inferior angle of the scapula, as well as generally receives a few fibers from it. The muscle curves around the lower border of the Teres major, as well as is twisted upon itself, to ensure that the superior fibers become at first posterior as well as then inferior, as well as the vertical fibers at first anterior as well as then superior. It ends inside a quadrilateral tendon, about 7 cm. long, which passes in front from the tendon of the Teres major, as well as is inserted into the bottom of the intertubercular groove of the humerus; its insertion extends higher on the humerus than that of the tendon of the Pectoralis major. The lower border of its tendon is united with that of the Teres major, the surfaces from the two being separated near their insertions by a bursa; an additional bursa is occasionally interposed between the muscle as well as the inferior angle of the scapula. The tendon of the muscle gives off an expansion towards the deep fascia of the arm.  (Henry Gray (1821–1865). Anatomy of the Human Body.)