Innervation of the scalenes is via C4-C6, and these muscles serve as accessory muscles of respiration. Finally, deep to the cervical fascia are the scalene muscles, which are a group of three accessory muscles that originate on the cervical vertebrae and insert on the first and second ribs. The omohyoid is composed of two muscle bellies, the tendon between which lies invested in the deep cervical fascia. The omohyoid muscle represents the superolateral border, and stretches from the scapula to the hyoid bone, passing behind the SCM. Anteromedially, the sternocleidomastoid (SCM) stretches from the sternum to the mastoid bone, and it is superficial to the fascial carpet. Two of the three borders of the supraclavicular fossa are muscles that are defining structures within the region. The platysma overlies the fascial carpet and receives innervated from the cervical branch of the facial nerve. Most superficially is the platysma, which is a thin muscle that stretches from the pectoralis and deltoid to the base of the mandible superiorly. The musculature of the supraclavicular is critical to understand, as muscles often serve as anatomic landmarks. Alternatively, if classified by region, these nodes would be classified as inferior deep cervical lymph nodes. Using the standardized classification of lymph nodes by levels within the neck, any lymph nodes within the supraclavicular fossa would be a designation of Level V lymph nodes. Of note, there are many lymph nodes within the supraclavicular fossa, the exact locations of which are highly involved and beyond the scope of this text. On the right, the primary lymphatic structure is the right lymphatic duct, which is responsible for draining lymph from the right thorax, right upper extremity, and right portion of the head and neck into either the subclavian vein or right internal jugular vein. On the left, the principal structure is the thoracic duct which collects lymph from the majority of the body before emptying into the origin of the brachiocephalic vein. The supraclavicular fossa houses differing lymphatic structures that vary by laterality. Of note, the fascia of the omohyoid muscle within the region separates the superficial suprascapular vein from the deep suprascapular artery. Venous structures in the supraclavicular fossa include the external and internal jugular veins as well as the corresponding structures for the aforementioned arterial structures (subclavian, suprascapular, and transverse cervical veins). Additionally, the transverse cervical and suprascapular arteries (branches of the subclavian) course through the fossa after branching from the first portion of the subclavian artery. The third segment, or the portion of the subclavian artery that runs distally to the anterior scalene muscle, is the portion within the supraclavicular fossa. The largest artery within the fossa is the subclavian, which is divided into three distinct segments by the anterior scalene muscle. The vasculature within the region of the supraclavicular triangle is complex, but critical to understand with regards to generating a differential diagnosis for pathology in the region.
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