Pectoral Region and Thoracoappendicular Muscles Anatomy

The pectoral region is the anterior part of the upper chest, located between the axilla and the deltoid muscle. It is characterized by the presence of four thoracoappendicular muscles, also known as pectoral muscles: the pectoralis major, pectoralis minor, serratus anterior, and subclavius. These muscles are involved in movements of the shoulder and arm and help stabilize these during fine motor movements.

The pectoralis major is the most superficial and largest muscle in the pectoral region, with attachments to the anterior surface of the sternum, superior six costal cartilages, and aponeurosis of the external oblique muscle. It extends across the upper part of the chest and attaches to the intertubercular sulcus of the humerus. The pectoralis major is responsible for adduction, depression, and rotation of the arm forward.

The pectoralis minor is a smaller muscle located underneath the pectoralis major and originates from the 3rd-5th ribs, inserting into the coracoid process of the scapula. It stabilizes the scapula by drawing it anteroinferiorly against the thoracic wall.

The serratus anterior is located more laterally in the chest wall and forms the medial border of the axilla region. It consists of several strips that originate from the lateral aspects of ribs 1-8 and attach to the costal surface of the medial border of the scapula. The serratus anterior rotates the scapula, allowing the arm to be raised over 90 degrees, and also protracts the scapula, holding it against the ribcage.

The subclavius is a small muscle located directly underneath the clavicle, running horizontally. It affords some minor protection to the underlying neurovascular structures.

Clinically, damage to the long thoracic nerve, which innervates the serratus anterior, can lead to a condition known as winging of the scapula, where the scapula protrudes out of the back due to the loss of its stabilizing function.