POSTERIOR
&
ANTERIOR
TRIANGLE OF NECK
Dr. H.A.Jaafar
Al-Nahrain Universitycollege of Medicine
Dept. Of Anatomy
Objectives:
At the end of this lecture we should be able to know :
1.The boundaries, roof, floor & contents of Anterior triangle
2.The boundaries, contents of posterior triangle
3.The role of Sternomastoid muscle in main anatomical division of the neck.
4.What are the careful and careless area of posterior triangle
5.What are the importance of diagastric and omohyoid muscles as a land
marks for subdivision of the two triangular regions of neck.
Posterior triangle
A. Posterior triangle
Is bounded by :



posterior border of sternocleidomastoid muscle,
anterior border of trapezius muscle,
superior border of clavicle.
roof ………formed by :
•
•
platysma
investing (superficial) layer of deep cervical fascia.
floor :…….formed by :



splenius capitis
levator scapulae muscles
anterior, middle, posterior scalene muscles.
Posterior cervical triangle
Trapezius
Sternocleidomastoid
Is divided into :……. by omohyoid posterior belly
I. occipital triangle.
II. subclavian (supraclavicular) triangle.
Contains:
1.accessory nerve,
2.cutaneous branches of cervical plexus,
3.external jugular vein,
4.transverse cervical
5.suprascapular vessels,
6.subclavian vein & artery,
7.Inferior belly of omohyoid,
8.roots and trunks of brachial plexus.
9.nerve to subclavius
10.dorsal scapular,
11.suprascapular,
12.long thoracic nerves.
Triangles of posterior (lateral)
region of neck
Triangles of posterior (lateral)
region of neck
trapezius muscle
Sternomastoid
muscle
Triangles of posterior (lateral)
region of neck
clavicle
Sternomastoid
muscle
Triangles of posterior (lateral)
region of neck
Occipital triangle
supraclavicular triangle
(greater supraclavicular fossa)
Triangles of posterior (lateral)
region of neck
Occipital triangle
supraclavicular triangle
(greater supraclavicular fossa)
Sternomastoid
muscle
Sternomastoid
muscle
trapezius muscle
Sternomastoid
muscle
trapezius muscle
clavicle
Omohyoid
muscle
Sternomastoid
muscle
trapezius muscle
clavicle
Omohyoid
muscle
Scalenus
anterior
muscle
Sternomastoid
muscle
trapezius muscle
clavicle
Omohyoid
muscle
Scalenus
medius
muscle
Sternomastoid
muscle
trapezius muscle
clavicle
Omohyoid
muscle
Sterno
thyroid m
Sternomastoid
muscle
trapezius muscle
clavicle
Omohyoid
muscle
thyrohyoid
m
Sternomastoid
muscle
trapezius muscle
clavicle
Omohyoid
muscle
Sternohyoid
m
Sternomastoid
muscle
trapezius muscle
clavicle
apex
trapezius
muscle
Investing
layer of
deep fascia
roof
Sternomastoid
muscle
Middle
1/3 of
clavicle –
base
Nerves in posterior triangle
1-Cervical
plexus
1- four muscular
branches
2- four cutaneous
branches
3- spinal root
of accessory
plexus
nerve (11th
cranial nerve )
2-Brachial
Roots , trunks and
their branches
1- dorsal scapular
nerve –c5(nerve to
rhomboids )
2- nerve to subclavius
– c5 &c6
3- nerve to serratus
anterior –c5,6 &7
It is the most
important
structure in the
occipital triangle
Spinal
part of
accessory
nerve
Platysma
Cutaneous nerves and superficial veins
Lesser occipital n.
External jugular vein
Greet auricular n.
Transverse nerve of neck
Anterior jugular vein
Supraclavicular n.
Anterior triangle
Anterior triangles
Suprahyoi
dmuscles
Infrrahyoid
muscles
Scalene muscles
Prevertebral muscles
B. Anterior triangle
Is bounded by:
 anterior border of sternocleidomastoid,
 anterior midline of neck,
 inferior border of mandible.
roof :……formed by:
•
•
platysma
investing layer of deep cervical fascia.
Is further divided by :
 omohyoid superior belly
 digastric anterior and posterior bellies
into :




digastric (submandibular),
submental (suprahyoid),
carotid,
muscular (inferior carotid) triangles.
Omohyoid
muscle
Sternomastoid
muscle
Omohyoid
muscle
Sternomastoid
muscle
Omohyoid
muscle
Sternomastoid
muscle
Omohyoid
muscle
Sternomastoid
muscle
apex
trapezius
muscle
Investing
layer of
deep fascia
roof
Sternomastoid
muscle
Middle
1/3 of
clavicle –
base
Anterior triangles
Suprahyoi
dmuscles
Infrrahyoid
muscles
Prevertebral muscles
Scalene muscles
Posterior
belly of
digastric
Stylohyoid
Anterior belly of
digastric muscle
Sternohyoid
muscle
Digastric triangle
Above …………….lower border of mandible
Below & infront …..anterior belly of Digastric muscle
Below & behind …..posterior belly of Digastric & stylohyoid
muscles .
Floor :
Anteriorly : ……..mylohyoid muscle
Posteriorly ………part of hyoglossus muscle
Contents of Digastric triangle
 submandibular salivary gland
 submandibular lymph nodes

lie on the surface of the gland
 facial artery
 deep to posterior end of submandibular salivary gland
 facial vein
 lies superficial to submandibular salivary gland
 hypoglossal nerve
 nerve to mylohyoid muscle
Anterior belly
of digastric
• d
Posterior
belly of
digastric
Mylohyoid
muscle
forms the
floor of
the mouth
Digastric triangle
Hyoid bone
C. Hyoid bone……..Is a U-shaped bone
consisting of :
 a median body,
 lesser horns (cornua) laterally, …………. paired
 greater horns (cornua) posteriorly……… paired
1. Body
Provides for attachments for :




Geniohyoid ,
mylohyoid,
Omohyoid ,
sternohyoid .
muscle
muscle
muscle
muscle
2. Greater horn
Provides attachments for :





middle constrictor,
hyoglossus,
digastric (anterior and posterior) bellies,
stylohyoid,
thyrohyoid muscle.
3. Lesser horn
Provides attachment for :
• stylohyoid ligament,
which runs from styloid process to lesser horn
Styloid process
D. Styloid process
 Is a slender projection of variable length
 extends downward & forward from temporal bone.
Gives origin to :
three muscles:



stylohyoid,
styloglossus,
Stylopharyngeus
two ligaments :
•
•
stylohyoid
stylomandibular.
Carotid triangle
boundary :
• Behind : …………..sternomastoid muscle
• Infront & above : posterior belly of digastric muscle
• Infront&below : superior belly of omohyoid muscle
Floor : infont : hyoglossus muscle ( above ) and the
thyrohyoid muscle (below)
• Behind: the middle constrictor muscle of the
pharynx (above ) and the inferior constrictor
muscle of the pharynx (below )
• d
Posterior
belly of
digastric
Carotid triangle
apex
trapezius
muscle
Investing
layer of
deep fascia
roof
Sternomastoid
muscle
Middle
1/3 of
clavicle –
base
Internal
carotid
artery
External carotid
artery
Common carotid
artery
Contents of the Carotid triangle
• 1- The carotid sheath and its contents :
• - common carotid artery : in the lower part
of the triangle .
• - internal carotid artery : in the upper part
of the triangle .
• Internal jugular vein : lateral
• Vagus nerve : between the artery and the
vein but in a more posterior plane .
• 2- the external carotid artery : gives
most of its branches in the carotid triangle
( superior thyroid artery ,lingual artery
,facial artery , ascending pharyngeal artery
and occipital artery )
• 3- hypoglossal nerve
• 4- Descendes cervicalis (C2,3) anterior to
carotid sheath.
• 5- sympathetic trunk adherent to the
posterior wall of carotid sheath
Contents of the Muscular
triangle
• It contains the infrahyoid muscle
Contents of the Submental
triangle
• 1- submental lymph nodes
• 2- beginning of the anterior jugular vein
The infrahyoid muscles
• They are strap like muscles occupy each side
of the midline of the neck , from the hyoid
bone to the manubrium sterni .
• They consist of 4 muscles arranged into 2
layers :
• 1- superficial layer : a- sternohyoid
• B- omohyoid
• 2- deep layer: a- sternothyroid
• B- thyrohyoid
Suprahyoid muscles
•
•
•
•
•
1- digastric muscle
2- mylohyoid muscle
3- hyoglossus muscle
4- geniohyoid muscle
5- stylohyoid muscle
Geniohyoid
muscle
Hyoglossus
Submendibular gland
Digastric
Accessory n.
Hypoglossal n.
Superior thyroid a.
Ansa cervicalis
Sternothyroid
Sternohyoid
Vagus n.
Cervical plexus
Phrenic n.
Omohyoid
III. Nerves
A. Accessory nerve
Is formed by union of :
• cranial &
• spinal roots.
Has both spinal and cranial portions,
traverse jugular foramen,
they interchange fibers.
cranial roots :
•
arise from medulla oblongata below roots of vagus.
spinal roots :
 arise from lateral aspect of cervical segment of spinal cord

between C1 – C5
 unites to form a trunk
 ascends between dorsal & ventral roots of spinal nerves in vertebral canal
 passes through foramen magnum.
cranial portion
 contains motor fibers .. join vagus nerve
 innervate soft palate, pharyngeal constrictors, & larynx.
spinal portion
 innervates sternocleidomastoid & trapezius muscles.
 Lies on levator scapulae in posterior cervical triangle
 passes deep to trapezius.
B. Cervical plexus
Is formed by ventral primary rami of C1 to C4.
1. Cutaneous branches
a- Lesser occipital nerve (C2)
• Ascends along posterior border of sternocleidomastoid to scalp
• behind auricle.
b- Great auricular nerve (C2-C3)
• Ascends on sternocleidomastoid
• innervate skin behind auricle & on parotid gland.
C- Transverse cervical nerve (C2-C3)
• Turns around posterior border of sternocleidomastoid
• innervates skin of anterior cervical triangle.
D-Supraclavicular nerve (C3-C4)
Emerges as a common trunk from under sternocleidomastoid
divides into anterior, middle, & lateral branches to skin over clavicle &shoulder.
2. Motor branches
Ansa cervicalis………………Is a nerve loop
formed by union of :
 superior root (C1)
 inferior root (C2--C3;
descendens hypoglossi
descendens cervicalis
.
Lies superficial to carotid sheath
in anterior cervical triangle.
Innervates infrahyoid (strap) muscles:
 omohyoid,
 sternohyoid,
 sternothyroid muscles,
with exception of
thyrohyoid muscle,
innervated by C1 via hypoglossal nerve.
Phrenic nerve (C3-C5)
Arises from chiefly from 4th cervical nerve;
contains :
 motor,
 sensory,
 sympathetic nerve fibers;
Provides:
 motor supply to diaphragm
 sensation to its central part.
• Descends on anterior surface of anterior scalene muscle
•
under cover of sternocleidomastoid muscle.
• Passes between subclavian artery & vein at root of neck
• enters thorax by crossing in front of origin of internal thoracic artery,
•
it joins pericardiacophrenic branch of this artery.
• Passes anterior to root of lung
•
•
between mediastinal pleura & fibrous pericardium
supply sensory fibers to these structures.
longus capitis and cervicis or colli,
sternocleidomastoid,
trapezius,
levator scapulae,
scalene muscles.
Accessory phrenic nerve (C5)
 arises as a contribution of :
 C5 to phrenic nerve or

a branch of nerve to subclavius (C5),
 descends lateral to phrenic nerve,
 enters thorax by passing posterior to subclavian vein,
 joins phrenic nerve below first rib to supply diaphragm.
C. Brachial plexus
 Is formed by union of ventral primary rami of C5 to T1
 passes between anterior scalene & middle scalene muscles.
1. roots give rise to :
Dorsal scapular nerve (C5)
o Emerges from behind anterior scalene muscle
o runs downward and backward through middle scalene muscle
o deep to trapezius.
o Passes deep to levator scapulae
o descends along with dorsal scapular artery on deep surface of rhomboid muscles
along medial border of scapula,
Innervating:
 levator scapulae
 rhomboid muscle.
Long thoracic nerve (C5--C7)
 Pierces middle scalene muscle,
 descends behind brachial plexus,
 enters axilla
innervate ……..serratus anterior.
C. Brachial plexus
2. Iupper trunk gives rise to :
Suprascapular nerve (C5-C6)
 Passes deep to trapezius
 joins suprascapular artery in a course toward shoulder.
 Passes through scapular notch under transverse scapular ligament.
Supplies :
• supraspinatus
• infraspinatus muscles
Nerve



to subclavius muscle (C5)
Descends in front of plexus and behind clavicle
innervate subclavius.
Communicates with phrenic nerve as accessory phrenic nerve
Omohyoid
muscle
Sternomastoid
muscle
apex
trapezius
muscle
Investing
layer of
deep fascia
roof
Sternomastoid
muscle
Middle
1/3 of
clavicle –
base
Posterior
belly of
digastric
Stylohyoid
Anterior belly of
digastric muscle
Sternohyoid
muscle