THE POSTERIOR TRIANGLE OF THE NECK

1. Splenius capitis - ligamentum nuchae and upper thoracic spinous vertebrae to the mastoid process and occipital bone (draws head backward or to the respective side).

2. Levator scapulae - processes of C1-C4 to the superior aspect of the medial border of the scapula (elevates scapula).

3. Scalenus muscles

All muscles of the posterior triangle, whether boundary or floor muscles, are enclosed by separate subdivisions of the deep investing fascia of the neck.

The posterior triangle of the neck can be further subdivided into:

• Occipital triangle lying above the inferior belly of the omohyoid
• Supraclavicular (Omoclavicular) triangle inferior to this muscle.

BOUNDARIES OF THE OCCIPITAL TRIANGLE:

CONTENTS OF THE OCCIPITAL TRIANGLE:

The lower four cervical nerves (C5,C6,C7,C8) are found in the scalene gap (space between scalenus anterior and scalenus medius muscles) and they, along with the first thoracic nerve (T1), make up the brachial plexus. Cervical nerves C5, C6, join to form the superior (upper) trunk of the brachial plexus, and these nerves as well as part of the superior trunk are found in the occipital triangle. Branches from the roots of C5, C6, and C7, as well as from the superior trunk include:

1. Dorsal scapular nerve - from the root of C5, pierces scalenus medius, and continues caudally on the deep surface of levator scapulae. This nerve innervates levator scapulae, rhomboids and it is accompanied by the dorsal scapular artery (deep branch of the transverse cervical artery).
2. Long thoracic nerve - from the roots of C5, C6, C7. Once formed, it passes posterior to the brachial plexus and then along the chest wall (close to the mid-axillary line) to innervate serratus anterior.
3. Superior trunk of the brachial plexus – Present in both triangles, this trunk will be discussed in detail in the next section

1. Suprascapular - through the suprascapular notch to innervate supraspinatus and infraspinatus

2. Middle trunk of the brachial plexus - this trunk is the continuation of the anterior primary division of the 7th cervical nerve.
3. Lower trunk of the brachial plexus - this trunk is formed from the anterior primary division of the 8th cervical and 1st thoracic nerves.
4. Subclavian artery (3rd part) - the first part of the subclavian artery lies medial to scalenus anterior, the second part lies posterior to this muscle, and the third part lies lateral to the scalenus anterior. The thyrocervical trunk arises from the first part of the subclavian, and two of its several branches (transverse cervical, suprascapular), pass through both the supraclavicular and occipital triangles in route to their destinations. The transverse cervical supplies trapezius, subscapularis, levator scapulae and the rhomboids, while the suprascapular supplies supra and infraspinatus. Occasionally there are no branches from the third part of the subclavian. An exception is when the descending scapular (dorsal scapular) arises from the second or third part of the artery (deep part of the transverse cervical artery).
5. External Jugular Vein: Derived from the Following Overview of venous drainage in the head and neck.

1. Superficial Temporal and Maxillary veins unite to form Retromandibular vein.
2. Retromandibular vein divides at angle of mandible into Anterior and Posterior divisions.
3. Anterior division joins Facial Vein to form Common Facial vein which drains into Internal Jugular vein.
4. Posterior division joins Posterior Auricular vein to form External Jugular vein.
5. External Jugular vein descends across Sternocleidomastoid muscle to drain into Subclavian vein.
6. Anterior Jugular vein forms from small veins below mandible;descends to join Ext. Jugular vein above clavicle. After lying superficial to the sternocleidomastoid muscle, the external jugular vein descends to the anterior angle of the posterior triangle where it enters the subclavian vein.

An important landmark in this region is the scalenus anterior muscle which passes from the anterior tubercles of C3 - C6 to its attachment at the scalene tubercle on the first rib.

Using scalenous anterior as a landmark Subclavian Artery is divided into three main parts with several important branches:

• Vertebral artery - arises from its upper posterior surface

• passes into the foramen transversarium of C6 and ascends, winds behind the lateral mass of the atlas and enters the skull at the foramen magnum. It unites with the vertebral artery from the opposite side to form the basilar artery.
• important since its has branches that also supply the cervical spinal cord

• Internal thoracic artery - arises opposite the vertebral artery posterior to the subclavian vein

• Runs in the pleura and enters the thorax on the posterior aspect of the sternum
• supplies anterior intercostal branches (running between the ribs) and terminates as the musculophrenic artery which supplies the diaphragm and superior epigastric artery which runs in the anterior abdominal wall.

• Thyrocervical trunk - Lateral to the musculophrenic artery and superior, breaks into inferior thyroid artery, suprascapular artery, and transverse cervical artery.

• Inferior thyroid artery passes upwards and medially toward the inferior pole of the thyroid gland. Immediately anterior to it lies the carotid sheath and, somewhat more medially, the middle cervical ganglion of the sympathetic trunk. It anastomoses with the superior thyroid artery coming from the external carotid artery. It supplies the scalenus anterior and the longus colli muscles by its ascending cervical artery.

• Suprascapular artery passes laterally across the posterior triangle to the upper border of the scapula. This artery may arise from the third part of the subclavian and in this situation may separate the superior from the middle and inferior trunks of the brachial plexus.
• Transverse (or Superficial) Cervical along with the suprascapular a. initially passes anterior to scalenus anterior and clamp down the phrenic nerve as they run into the posterior triangle of the neck

• Costocervical artery: (on the left it generally arises from the first part) passes posteriorly over the apex of the lung to give 2 branches:

• Superior/Highest Intercostal artery to supply first two intercostal spaces with Posterior Intercostal arteries

• Deep Cervical Artery to deep musculature for the back of the neck.

• Dorsal scapular artery passes laterally through the brachial plexus and passing deep tot he levator scapulae it reaches the scapula and descends deep to the rhomboids with the dorsal scapular nerve. This artery may arise from the thyrocervical trunk as the deep portion of the transverse cervical artery.