Classification and Architecture
The subclavius belongs to the group of superficial thoracic muscles (mm. thoracis). Embryologically, it originates from the upper limb musculature.
- Origin: Arises from the first rib (costa I) near its junction with the costal cartilage.
- Insertion: Inserts into the groove on the inferior surface of the middle third of the clavicle (sulcus m. subclavii).
Topography and Fascial Compartments
Together with the clavicle, the muscle serves as an osteomuscular landmark for the axilla. On a sagittal section of the subclavian region, structures are arranged in the following sequence from superficial to deep:
- Bony structures: Clavicle.
- Muscles: Subclavius, pectoralis major (m. pectoralis major), pectoralis minor (m. pectoralis minor), and serratus anterior (m. serratus anterior).
- Fascia and adipose tissue: Subpectoral space, pectoral fascia, clavipectoral fascia, axillary fascia, endothoracic fascia, and axillary fat pad.
- Internal structures: Parietal pleura, along with the axillary artery and vein.
The clavipectoral fascia (fascia clavipectoralis) forms osteofibrous sheaths for two muscles: the pectoralis minor and the subclavius. Superiorly, the pectoral fascia (fascia pectoralis) attaches to the fascia of the subclavius and the superficial layer of the deep cervical fascia. Posterior to the clavicle, a portion of the deep cervical fascia covering the anterior scalene muscle attaches to the first rib.
Relation to the Neurovascular Bundle
The subclavius overlies the origin of the axillary artery (a. axillaris), which is the direct continuation of the subclavian artery. The origin of the axillary artery lies deep to the clavicle within the clavipectoral triangle (trigonum clavipectorale).
The axillary artery is divided into three parts:
- Part 1 — from the lateral border of the first rib to the superior border of the pectoralis minor muscle.
- Part 2 — posterior to the pectoralis minor muscle.
- Part 3 — from the inferior border of the pectoralis minor muscle to the inferior border of the teres major muscle.
For the first part of the axillary artery, specific relations include: it rests on the superior digitations of the serratus anterior muscle and is covered anteriorly by the clavipectoral fascia. The axillary vein (v. subclavia) lies anterior and medial to it, while the trunks of the brachial plexus (plexus brachialis) lie anterior and lateral to it.
Blood Supply, Innervation, and Function
- Blood supply: Thoracoacromial artery (a. thoracoacromialis) and superior thoracic artery (a. thoracica superior).
- Innervation: Nerve to subclavius (n. subclavius), spinal roots C5–C6.
- Function: Depresses the clavicle and pulls it medially; stabilizes the sternoclavicular joint during movements of the shoulder girdle.