Latissimus dorsi muscle
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The latissimus dorsi muscle is a large, wide, flat muscle on the posteroinferior aspect of the back. It has the shape of a triangle that has a base at the thoracolumbar spine and its apex in the axillary region.
This muscle has a wide origin by tendons that attach to the spinous processes of the lower six or seven thoracic vertebrae as well as those of the lumbar vertebrae, the sacral crest, and the posterior aspect of the external lip of the iliac crest. This created a wide fibrotendinous lamina known as the thoracolumbar fascia. The muscle also attaches to the external surface of the three or four inferiormost ribs and the inferior angle of the scapula.
From here, the muscle fibers converge superolaterally and twist anterosuperiorly to form a quadrilateral tendon that inserts deep into the bicipital groove (Lat: sulcus intertubercularis) of the humerus as shown by number 5 in the accompanying figure. There is sometimes a tendinous extension to the humeral lesser tubercle.
The latissimus dorsi extends, adducts, and medially rotates the shoulder joint, also known as the glenohumeral joint. Along with the teres major muscle they are known as the “handcuff muscles”, as this is the action of these muscles as the hands are brought together towards the back. The latissimus dorsi is innervated by the thoracodorsal (or long subscapular) nerve (C6, C7, and C8).
The Terminologia Anatomica 2 proper name is “musculus latissimus dorsi”. The plural form is “musculi latissimi dorsi”. The name of the muscle is derived from Latin. Since “latum” means “wide”, “musculus latissimus dorsi” means the “widest muscle of the back”, quite a proper name. In other languages this is more evident. In Spanish, the name for the muscle is [músculo dorsal ancho] meaning the “wide muscle of the back”.
The latissimus dorsi is one of the 17 muscles that attach to the scapula. It also forms one of the borders of the lumbar triangle of Petit, potential site for a lumbar hernia.
Sources:
1. “Gray’s Anatomy” Henry Gray, 1918
2. "Tratado de Anatomia Humana" Testut et Latarjet 8th Ed. 1931 Salvat Editores, Spain
3. "Gray's Anatomy" 42nd British Ed. Churchill Livingstone 2021
4. “An Illustrated Atlas of the Skeletal Muscles” Bowden, B. 4th Ed. Morton Publishing. 2015
5. "Trail Guide to The Body" 4th. Ed. Biel, A. Books of Discovery. 2010