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The muscles of the ventral trunk include the muscles of the thoracic cage, as well as the muscles of the anterior, posterior and lateral abdominal muscles.
The external and internal intercostal muscles, are innervated by the intercostal nerves (T 1 - T 11). The external intercostal muscles function to elevated the rib cage during inspiration and the internal intercostal muscles function to lower the rib cage during expiration. The subcostal muscles assist the internal intercostal muscles and they have their origins on the inner surface of one rib and go on to attach to inner surface of the next rib or the rib below that. The transversus thoracis muscles originate from the posterior aspect of the xiphoid process and the lower part of the sternum, and insert on the costal cartilages of the third to sixth ribs. The superior fibers of the serratus anterior muscles originate from the spinous processes of C 7 - T 3 vertebrae and insert on the superior border of the second to fourth ribs, while the inferior fibers arise from the spinous processes of the T 11 - L 2 vertebrae and insert on the lower borders of the eighth to twelfth ribs.
The subclavius muscle has its origin on the first rib, its insertion on inferior surface of the lateral clavicle and it is innervated by the subclavian nerve.
The pectoralis major muscle has its origins on the medial half of the clavicle, the sternum, the second to seventh costal cartilages and anterior layer of the rectus sheath. It inserts on the crest of the greater tubercle of the humerus. The pectoralis minor muscle arises from the third to fifth ribs and inserts on the coracoid process of the scapula. Both the pectoralis major and minor muscles are innervated by the pectoral nerves (C 6 - T 1).
The external abdominal oblique, internal abdominal oblique, transversus abdominis and the rectus abdominis muscles are also innervated by the intercostal nerves T 5 - T 12. The cremaster muscle is innervated by the genitofemoral nerve and the pyramidalis is innervated by the subcostal nerve.
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