The musculus pectoralis major, also known as the large chest muscle, is an important muscle on the front of your chest. It consists of two usually contiguous parts (1, 2, 3, 4) (Pars clavicularis and Pars sternocostalis (1, 2, 3, 4)) with fibers that are also referred to as pars abdominalis (1, 2, 3). These parts have different fiber courses and are sometimes separated by a groove. On their way to the humerus, its muscle fibers form the rounded anterior axillary fold (1, 2, 3, 4). The muscle’s name is derived from Latin. “Pectoralis” means “belonging to the chest” and is the adjective of “pectus,” which means chest. “Major” means “larger” and is the comparative of “magnus.” It refers to its location and size compared to the Musculus pectoralis minor, the smaller chest muscle (1). But enough about the name; let’s take a closer look at the great pectoral muscle! In this article, you will learn everything about the origins, attachments, functions, and peculiarities of this fascinating muscle.

Musculus pectoralis major – Origin and insertion

The musculus pectoralis major, which lies very superficially on the anterior chest wall, is a large, fan-shaped muscle that shapes the chest wall relief. It has two parts that are normally connected: the pars clavicularis and the pars sternocostalis. The clavicular part (pars clavicularis) is the smaller part and originates ventrally on the medial (toward the middle) half of the clavicle. It runs distally (away from the body center) to the crista tuberculi majoris of the humerus. The sternocostal head (pars sternocostalis) is the larger part and originates ventrally on the manubrium (handle of the sternum) and corpus sterni (body of the sternum), on the six upper rib cartilages, on the anterior part of the 6th rib and on the aponeurosis of the m. obliquus externus abdominis. The fibers that originate from the aponeurosis are distinguished as the pars abdominalis, but are typically not differentiated as a third head in medical literature. The musculus pectoralis major narrows from this wide medial origin to a tendinous plate that inserts laterally (sideways) of the sulcus intertubercularis (depression between two bony bumps on the upper arm; the bumps are: greater tubercle, tuberculum majus and lesser tubercle, tuberculum minus) humeri at the crista tuberculi majoris. The fibers cross each other at their insertion point when the arm is hanging, forming the anterior sheet of the tendinous plate by the fibers of the pars clavicularis and the posterior sheet by the fibers of the pars sternocostalis and pars abdominalis. The tendinous plate thus has a U-shaped cross-section. The posterior (sternocostal) part of the muscle enters into the capsule of the shoulder joint, and the anterior (clavicular) part into the insertion of the musculus deltoideus. The fibers of the pars sternocostalis also produce the anterior axillary fold on their way to the humerus. The m. pectoralis major covers the most superficial muscle of the anterior chest wall, the m. pectoralis minor, m. serratus anterior and ribs. In women, the breast gland (mamma) is located over the muscle (1, 2, 3).

The nerve supply of the musculus pectoralis major is provided by the nn. pectorales medialis and lateralis. The clavicular part of the muscle receives its innervation from the spinal nerves C5 and C6, while the sternocostal and abdominal parts are supplied from the spinal nerves C7, C8, and Th1 (3).

Musculus pectoralis major – Functions

The musculus pectoralis major is a powerful and versatile muscle that moves the upper arm and the chest. It has different parts that have different functions. The upper part helps to bring the arm forward, for example, when hugging or boxing. The middle and lower part helps to bring the arm to the side, for example, when swimming or clapping. Both parts together help to rotate the arm inward, for example, when opening a door or screwing. In addition, both parts can bring the arm down from the raised position, for example, when supporting or climbing down. The musculus pectoralis major is the most important muscle for these movements in the shoulder joint, which requires a lot of strength. It works with other muscles that move the arm backward and inward or push the shoulder girdle forward. The m. pectoralis major can also facilitate breathing by lifting the sternum and ribs with a fixed arm and thus letting more air into the lungs (1, 2, 3).

If you want to learn more about the anatomy and function of the muscles, feel free to check out other articles on my blog, such as the anatomy of the musculus triceps brachii. I appreciate your feedback and questions in the comments. You may also find interesting videos on fitness & co on my YouTube channel.

References

1. Sobotta, J. (2017). Sobotta, Atlas der Anatomie Band 1: Allgemeine Anatomie und Bewegungsapparat. Deutschland: Urban & Fischer in Elsevier.

2. Waschke, J., Böckers, T. M., & Paulsen, F. (Eds.). (2019). Sobotta Lehrbuch Anatomie. Elsevier Health Sciences.

3. Palastanga, N., & Soames, R. (2014). Anatomie und menschliche Bewegung: Strukturen und Funktionen. Elsevier, Urban&FischerVerlag.

4. Thompson, K., Kwon, Y., Flatow, E., Jazrawi, L., Strauss, E., & Alaia, M. (2020). Everything pectoralis major: from repair to transfer. The Physician and Sportsmedicine, 48(1), 33-45.