Anterior Triangle

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The anterior triangle is bounded by the anterior border of the sternocleidomastoid muscle, the anterior midline, and the body of the mandible (Figure 10-6-1). Subdivisions of the anterior triangle contain the strap muscles, the submandibular gland, the common carotid, internal carotid and external carotid arteries, and parts of cranial nerves X and XII. The strap muscles consist of a series of five pairs of muscles which have attachments to bony or cartilaginous structures adjacent to the midline beginning at the sternum and extending to the underside of the mandible. Strap muscles act on the mandible, hyoid bone, and thyroid cartilage.

Cervical plexus

There are two major muscular branches of the cervical plexus, the ansa cervicalis and the phrenic nerve. The cervical plexus is formed by the ventral rami of spinal nerves from CI through C4 and is situated behind the sternocleidomastoid muscle and in front of the scalenus medius and levator scapulae muscles.

Ansa Cervicalis

The ansa cervicalis is a loop formed by fibers from CI (the superior root), which courses infe-riorly by hitchhiking with fibers of the hypoglossal nerve to join fibers from C2 and C3 (the inferior root). The fibers of the ansa are distributed to three strap muscles (sternohyoid, both bellies of omohyoid, and sternothyroid). The thyrohyoid and geniohyoid are strap muscles innervated by CI fibers.

Clinical Correlate

The most significant artery of the external carotid system is the middle meningeal artery. It arises from the maxillary artery in the infratemporal fossa and enters the skull through the foramen spinosum to supply skull and dura. Lacerations of this vessel result in an epidural hematoma.

Carotid triangle

The carotid triangle is a subdivision of the anterior triangle. The carotid triangle contains the internal jugular vein, the vagus nerve (CN X),and the common or internal and external carotid arteries. All of these structures are found in the carotid sheath.

Head and Neck

Superficial temporal Posterior auricular Occipital

Internal carotid External carotid Common Carotid

Transverse cervical Suprascapular Subclavian

Lymph Nodes Neck

Maxillary

Facial

Lingual

Superior thyroid

Inferior thyroid Vertebral

Thyrocervical trunk Costocervlcal trunk Internal thoracic

Figure 111-6-3. Arteries to the Head and Neck

Superficial temporal Posterior auricular Occipital

Internal carotid External carotid Common Carotid

Transverse cervical Suprascapular Subclavian

Maxillary

Facial

Lingual

Superior thyroid

Inferior thyroid Vertebral

Thyrocervical trunk Costocervlcal trunk Internal thoracic

Figure 111-6-3. Arteries to the Head and Neck

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