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Ventral trunk

Ventral trunk

The trunk is the central part of the body from which the neck and limbs extend. Its ventral aspect includes a group of structures that define the anterior portion of the thorax and abdomen. These structures consist of skin and subcutaneous tissue, bony and muscular elements, vessels and nerves. The elements of the ventral trunk protect, support and compress the vital organs of the thorax and abdomen, as well as serve as an attachment site for various muscles including those that are responsible for maintaining posture and moving the upper limb.

Bones

The skeletal system of the ventral trunk consists mainly of the sternum and clavicle.  In an adult, the sternum is comprised of three structures: the broad and superiorly placed manubrium; the narrow and longitudinal body of sternum; and the small inferiorly placed xiphoid process. The clavicle, or the collarbone in layman terms, is a bone that joins the ventral trunk with the upper limb. The medial half of its shaft has an enlarged triangular sternal end that articulates with the manubrium of the sternum at the sternoclavicular joint.

Muscles

Thoracic Muscles

The ventral trunk is defined by both thoracic and abdominal muscles.  Muscles of the anterior portion of the thoracic wall alter the rib and sternum positions to change the thoracic volume during breathing, and reinforce the thoracic wall. They are made up of six muscles. The intercostal muscles are flat muscles found between each of the intercostal spaces. The subcostalis muscles span multiple ribs and extend between the internal surface of one rib to the internal surface of another. The transversus thoracis muscles are thin muscles found in the inner surface of the anterior thoracic wall. Moreover, there is the serratus anterior muscle that can be divided into three parts: superior, intermediate and inferior. It is a fan-shaped muscle found in the anterolateral wall of the thorax. Muscles in the pectoral region also belong to the anterior portion of the thorax. They define the chest, and contain the pectoralis major, pectoralis minor and the subclavius muscles. The pectoralis major is the largest and most superficial, while the pectoralis minor and subclavius lie beneath it. The cremaster muscle is formed by the abdominal musculature. It originates from the inguinal ligament and covers the spermatic cord and testes in the human male.

Abdominal Muscles

There are five muscles in the anterolateral group of abdominal wall muscles. Each has a specific action, but together they form a firm yet flexible wall that keeps the abdominal viscera within. They also participate in the breathing process, as well as in any action that requires an increase in intra-abdominal pressure. The two vertical muscles of this group are the rectus abdominis and pyramidalis muscles. The rectus abdominis is a long flat muscle that spreads along the length of the abdominal wall, while the pyramidalis is a small triangular muscle that lies anterior to the rectus abdominis. The other three muscles are flat muscles including the external oblique, internal oblique, and the transversus abdominis.  The external oblique is the most superficial of the three and lies directly deep to the superficial fascial covering. The internal oblique is smaller and thinner than the external oblique, and lies deep to it. While the transversus abdominis blends with the linea alba at the midline of the abdominal wall, deep to the internal oblique muscle.

Neurovasculature

The vasculature of the ventral trunk includes the internal thoracic, lateral thoracic, anterior intercostal, superior and inferior epigastric arteries, and all the associated veins parallel to their pattern. Its nervous supply consists mainly of the brachial plexus, lateral and medial pectoral, subcostal, genitofemoral, iliohypogastric, and ilioinguinal nerves.

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