The<unk><unk>  is a triangular, flat muscle, which covers the lumbar region and the lower half of the thoracic region, and is gradually contracted into a narrow fasciculus at its insertion into the humerus.
It arises by tendinous fibers from the spinous processes of the lower six thoracic vertebrae and from the posterior layer of the lumbodorsal fascia, by which it is attached to the spines of the lumbar and sacral vertebræ, to the supraspinal ligament, and to the posterior part of the crest of the ilium.
It also arises by muscular fibers from the external lip of the crest of the ilium lateral to the margin of the sacrospinalis, and from the three or four lower ribs by fleshy digitations, which are interposed between similar processes of the obliquus abdominis externus.
From this extensive origin the fibers pass in different directions, the upper ones horizontally, the middle obliquely upward, and the lower vertically upward, so as to converge and form a thick fasciculus, which crosses the inferior angle of the scapula, and usually receives a few fibers from it.
The muscle curves around the lower border of the teres major, and is twisted upon itself, so that the superior fibers become at first posterior and then inferior, and the vertical fibers at first anterior and then superior.
It ends in a quadrilateral tendon, about 7 cm. long, which passes in front of the tendon of the teres major, and 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 of the two being separated near their insertions by a bursa; another bursa is sometimes interposed between the muscle and the inferior angle of the scapula.
The tendon of the muscle gives off an expansion to the deep fascia of the arm.
Latissimus dorsi muscle
Sartorius muscle
Pubococcygeus muscle
Splenius capitis muscle
Levatores costarum muscles
Gluteus medius muscle
Quadratus plantae muscle
Levator scapulae muscle