1. Scalenus Anterior
Origin: From the transverse processes of the 3rd; 4th ; 5th and 6th cervical vertebrae.
Insertion: Into the scalene tubercle on the inner border of the 1st rib and into the ridge on the upper surface of the 1st rib.
Nerve Supply: From the anterior rami of the 4th; 5th and 6th cervical nerves.
Action: It assists in elevation the 1st rib. When acting from below, it laterally flexes the cervical part of the vertebral column.

2. Relation of scalenus anterior muscle Anteriorly:
The prevertebral layer of deep cervical fascia, which binds the phrenic nerve down to the anterior surface of the muscle; the superficial cervical and suprascapular arteries which cross the phrenic nerve; and the internal jugular and subclavian veins.
Posteriorly:
The subcalvian artery; brachial plexus and the cervical dome of the pleura.
Medially:
The vertebral artery&vein; inferior thyroid artery; thyrocervical trunk; sympathetic trunk and on the left side, thoracic duct.
Laterally:
The roots of the phrenic nerve unite at the lateral border of the muscle at the level of the cricoid cartilage. Then it descends on its anterior surface. The roots of the brachial plexus & subclavian artery emerge from behind the lateral border of it to enter the posterior triangle of neck.

3. Scalenus Medius
Origin: From the transverse processes of the upper six cervical vertebrae.
Insertion: Into the upper surface of the 1st rib behind the groove for the subclavian artery.
It lies behind the roots of the brachial plexus and behind the subclavian artery.
Nerve Supply: Branches from the anterior rami of the cervical nerves.
Action: like scalenus anterior.

4. Scalenus Posterior
Origin: From the transverse processes of the lower cervical vertebrae.
Insertion: Into the outer surface of the second rib.
Nerve supply: branches from the anterior rami of the lower cervical nerves.
Action: Elevates the 2nd rib. When active from below, it laterally flexes the cervical part of the vertebral column.

5. Anterior vertebral ( prevertebral ) muscles4 3 2 1
Anterior vertebral ( prevertebral ) muscles
1- Longus coli.
2- Longus capitis.
3- Rectus capitus anterior.
4- Rectus capitus lateralis.

6. Longus Colli Muscle Origin:
Anterior tubercle of C1, bodies of C1 to C3 and transverse processes of C3 to C6 vertebrae
Insertion:
Bodies of C5 to T3 vertebrae, transverse processes of C3 to C5 vertebrae
Action:
Flexes neck with rotation to opposite side

7. Longus Capitis Muscle Origin: Basilar part of occipital bone
Insertion:
Anterior tubercles of C3 to C6 transverse processes
Action:
Flexes the head

8. Rectus Capitis Anterior
Origin:
Base of the skull, just anterior to the occipital condyle
Insertion:
Anterior surface of lateral mass of atlas
Action:
Flexes the head

9. Rectus Capitis Lateralis
Origin:
Jugular process of occipital bone
Insertion:
Transverse process of atlas
Action:
Flexes head and helps stabilize it

10. Scaleno-vertebral triangle Its boundaries are the Longus colli ; scalenus anterior and the transverse process of 6th cervical vertebra. It contains 1st part of subclavian artery ; sympathetic chain ; vertebral artery and the thoracic duct ( on left side ).

11. Cervical plexus
It is formed by anterior rami of 1, 2, 3 ; 4 cervical nerves.
The rami are joined by connecting branches forming a loops on the levator scapulae and scalenus medius muscles.
It is covered by the prevertebral fascia. It is related to the internal jugular vein within the carotid sheath.

12. Branches:
1- Cutaneous
lesser occipital; greater auricular; transverse cutaneous and supraclavicular nerves.
2- Phrenic nerve to the diaphragm
2- Muscular
- Prevertebral muscles Sternocleidomastoid (C2 & C as proprioceptive ).
- Levator scapule (C3&C4motor
- Trapezius ( C3 & C4 as proprioceptive ).
- A branch of C1 joins the hypoglossal nerve then it leaves it to supply the thyrohoid & geniohyoid.
- Some of C1 fibers (descending branch) unites with the descending cervical nerves of C2& C3 to form the ansa cervicalis which supplies omohyoid; sternohyoid and sternothyroid muscles. C2

13. Phrenic Nerve
It arises from the 3rd ; 4th and 5th cervical nerves of cervical plexus It runs vertically downward acrosses the front of the scalenus anterior from its lateral to medial border behind the prevertebral layer of deep cervical fascia It enters the thorax by passing in front of the subclavian artery and behind the beginning of the brachiocephalic vein.

14. Relations
Anteriorly:
The prevertebral layer of the deep fascia; internal jugular vein; superficial cervical and suprascapular arteries; beginning of the brachiocephalic vein and on the left side the thoracic duct.
Posteriorly:
The scalenus anterior; subclavian artery and the cervical dome of pleura.

15. Branches:
1- It is the only motor nerve supply to the diaphragm.
2- It contains sympathetic fibers.
3- It contains proprioceptive sensory fibers ( stimulation of the sensory nerve ending in the muscles& tendons and joints ) for the muscles of the diaphragm.
4- It contains sensory fibers for the mediastinal pleura and the pericardium.
5- It contains Sensory fibers for the pleura & peritoneum covering the upper and lower surfaces of the central part of the diaphragm.