The scalenus anterior muscle originates on the cervical vertebrae and inserts on the first rib. It acts to elevate the first rib and bend the neck laterally. The triangle of the vertebral artery is bounded by the scalenus anterior muscle medially, the longus colli muscle laterally, and the subclavian artery inferiorly. It contains the vertebral artery, veins, and nerves like the phrenic nerve and brachial plexus branches.

1. Scalenus Anterior Muscle
Dr M Idris Siddiqui
TRIANGLE OF VERTEBRAL ARTERY

4. Scalene anterior
• Key structure in lower neck.
• Lies deep to sternocleidomastoid at the side of neck.
Origin:
• By 4 slips from anterior tubercles of C3-C6 transvers
processes.
Insertions:
• Tapers to insert on scalene tuberclr on inner border of
1st rib.
Nerve supply:
• C3,4,5 anterior primary rami
Actions:
• Elevates 1st rib, if 1st rib is fixed, bends neck on same
side.

5. • A triangular interval (inverted V) or pyramidal
gap.
• It is triangle of vertebral artery.
• It is roofed over by sternocleidomastoid.
• Its lateral margin is medial border of scalene
anterior.
• Its medial margin is lateral border of longus
colli.
• Apex lies at carotid tubercle(on transverse
process of C6)
• The base is subclavian artery which is divided
into 3 parts
• Part 1: medial to Scalene anterior
• Part 2: behind Scalene anterior
• Part 3: lateral to Scalene anterior.

6. Scalenus anterior
• Scalenus anterior lies at the side of the
neck deep (posteromedial) to SCM.
• Above, it is attached by musculotendinous
fascicles to the anterior tubercles of the
transverse processes of the third, fourth,
fifth and sixth cervical vertebrae.
– These converge, blend and descend almost
vertically, to be attached by a narrow, flat tendon to
the scalene tubercle on the inner border of the first
rib, and to a ridge on the upper surface of the rib
anterior to the groove for the subclavian artery.

7. • The site of insertion is marked by
a bump--the scalene tubercle--
that also separates two grooves
on the upper surface of the 1st rib.
The groove posterior to the
scalene tubercle is caused by
passage of the subclavian artery
and the 1st thoracic ventral ramus.
The groove anterior to the scalene
tubercle is caused by the
subclavian vein.

9. Triangle of the vertebral artery
• Scalenus anterior muscle
• Longus colli muscle
• The superior aspect of the subclavian
artery
–The space between these scaleni
muscles is called the interscalene
triangle. Its base is formed by the
groove for the subclavian artery on the
1st rib.

11. Cervical (1st
) Part • extends from origin to tnvs process of CV7
• enters foramen in tnvs process of CV6
• Ant. relations 1. carotid sheath & CCA
2. vertebral vein
3. inf thyroid artery
4. on L side: thoracic duct
• Post. relations 1. tnvs process of CV7
2. stellate ganglion
3. ventral rami of CV7, 8
Vertebral (2nd
)
Part
extends from tnvs processes of CV6 to CV1
Ie.runs through the foramina of the upper 6 CV emerge from
tnvs process of atlas
Suboccipital (3rd
)
Part
• winds medially bhd lat mass of atlas
• enters vertebral canal after piercing dura mater & arachnoid
mater
• passes through foramen magnum  then makes a sharp loop
Intracranial (4th
)
Part
• asc medially in front of medulla oblongata
• at lower border of pons, the vertebral arteries
unite to form the basilar artery
Vertebral artery

12. Direct anterior relations
• Its anterior surface is covered by prevertebral fascia-the only
structure fascia & muscle -in front- is the phrenic nerve.
• One important nerve, one muscle, two arteries & two large
veins are related to ant. surface of scalenus ant.
• The phrenic nerve, PVF plasters it against ant. surface. The
nerve runs from lateral border to medial border.
• One muscle & two arteries(arranged from above downwards)
– The inferior belly of omohyoid muscle
– The transverse cervical artery
– The supra scapular artery
• Two arteries are along with anterior jugular vein)
• Two large veins & a small vein
– The subclavian vein
• Crosses the external jugular vein
– The internal jugular vein
• (in carotid sheath) overlaps the medial part of anterior surface the muscle

13. Posteriorly
• The suprapleural membrane.
• The pleura,
• The origin of the brachial plexus
• The second part of the subclavian artery.
• The scalenus medius muscle lies behind the scalenus anterior
muscle. The the brachial plexus, the subclavian artery separate
scalenus anterior from scalenus medius.
• Below its attachment to the sixth cervical vertebra, the medial
border of the muscle is separated from longus colli by an
angular interval in which the vertebral artery and vein pass to
and from the foramen transversarium of the sixth cervical
vertebra.
– (The proximity of the muscle to the brachial plexus, subclavian artery
and vein can give rise to compression syndromes).

14. Medial relations
(inverted V-shaped space,the apex of which is carotid tubercle)
• The medial border of the muscle is related to
– The 1st
part of subclavian artery
• Crosses lower part of inverted v-shaped space(as it passes from behind
sternoclavicular joint to disappear behind medial border of scalenus ant. to
become 2nd
part of the artery)
– The vertebral artery
• Runsupwards to the apex of inverted v-shaped space to enter foramen
transversarium of C6.
– The inferior thyroid artery
• It has an inverted U course on its way to reach post. border of thyroid gland.
• On the left side, the medial border is related to the
thoracic duct.
• It crosses the triangular interval at the level of the seventh cervical
vertebra crosses

15. Laterally
– The emerging branches of the cervical plexus
– The roots of the brachial plexus,
– The third part of the subclavian artery.

17. Innervation
•Scalenus anterior is
innervated by branches
from the ventral rami of
the fourth, fifth and sixth
cervical spinal nerves.

18. Actions
• Acting from below, scalenus
anterior bends the cervical portion
of the vertebral column forwards
and laterally and rotates it
towards the opposite side. Acting
from above, the muscle helps to
elevate the first rib.

19. Contents of the triangle of the vertebral artery
1. The vertebral artery and vein ascend to the apex
of triangle and enter the foramen transversarium of
C6.
2. The sympathetic trunk (on the anterior aspect of
longus colli) with associated middle (at the level of
the inferior thyroid artery) and inferior cervical
ganglia (on the posterior aspect of the origin of the
vertebral artery).
3. The common carotid artery runs on the anterior
aspect of the triangle to lie anterior to the origins of
scalenus anterior. It can be compressed on the
transverse process of C6 (the carotid tubercle).
4. The carotid sheath contains the common carotid
artery, internal jugular vein and vagus nerve. It is
located on the medial border of the scalenus
anterior.

20. Contents of the triangle of the vertebral artery
5. The right recurrent laryngeal nerve arises from the
vagus and loops under the right subclavian artery to
ascend to the larynx between the trachea and the
esophagus.
The most inferior aortic arch retained in embryonic
development on the right is the 4th aortic arch and it
forms the initial segment of the right subclavian artery.
On the left side, the 6th aortic arch is retained as the
ductus arteriosus and the left recurrent laryngeal nerve
loops around it.
6. The phrenic nerve lies in the inferolateral corner of the
triangle on the anterior surface of the subclavian artery. It
crosses the anterior surface of the subclavian artery and
the apex of the lung to enter the thorax.
7. The left phrenic nerve is crossed by the thoracic duct
which joins the bifurcation of the left brachiocephalic vein.
8. The right lymphatic duct joins the bifurcation of the right
brachiocephalic vein