The posterior belly of the digastric muscle originates from the mastoid notch of the temporal bone and inserts on the intermediate tendon which connects to the hyoid bone. It has relationships superiorly with the external carotid artery branches and inferiorly with the internal carotid artery, internal jugular vein and cranial nerves IX, X, XI, XII. The posterior belly is supplied by the posterior auricular and occipital arteries and innervated by the facial nerve.

1. The digastric triangle
Submandibular triangle

3. •Contains the superficial lobe of the
submandibular (submaxillary) salivary gland.
•Its floor is formed by
•The mylohyoid,
•The hyoglossus and
•The middle constrictor muscles
The digastric triangle

5. Digastric (Submandibular) Triangle
• A digastric triangle is bounded by
– (1) The posterior belly and intermediate tendon of
the digastric,
– (2) The anterior belly of the digastric, and
– (3) The lower border of the mandible.
Since the posterior belly of the digastric is
coincident with a line between the angle of the
mandible and the mastoid process.
– The digastric triangle does not exist posterior to the mandible.
– Thus, for all practical purposes, the posterior border of the digastric
triangle is formed solely by the intermediate tendon of the digastric.

6. The submandibular region
• It is the region between the body of the
mandible & the hyoid bone.
• It is almost totally hidden from view by the
submandibular gland.
• Superficial part includes submental &
digastric triangles.

7. Submandibular fossa
• The Submandibular Gland occupies the
submandibular fossa on the inner
aspect of the mandible & extends into
• The mental foramen-----in front
• The angle of mandible---behind
• The mylohyoid line -------above
• May overlap two bellies of digastric
muscles

9. Muscle Origin Insertion Innervation Main Action(s)
Digastric Anterior
belly:
digastric
fossa of
mandible
Posterior
belly:
mastoid
notch of
temporal
bone
Intermediate
tendon to body
and greater horn
of hyoid
Anterior belly:
Nerve to
mylohyoid, a branch
of inferior alveolar
nerve
Posterior belly:
Digastric branch of
(preparotid) facial
nerve (CN VII)
Working with
infrahyoid muscles,
depresses mandible
against resistance;
elevates and steadies
hyoid during
swallowing and
speaking

11. Digastric muscle
• Each digastric muscle has two bellies, joined by an
intermediate tendon, that descends toward the hyoid.
A fibrous sling derived from the pretracheal layer of deep cervical fascia allows the
tendon to slide anteriorly and posteriorly as it connects this tendon to the body and
greater horn of the hyoid.
• The difference in nerve supply between the anterior
and posterior bellies of the digastric muscles results
from their different embryological origin from the 1st
and 2nd pharyngeal arches, respectively. CN V
supplies derivatives of the 1st arch, and CN VII
supplies those of the 2nd arch.

12. Digastric muscle
• Digastric has two bellies and lies below the mandible,
extending from the mastoid process to the chin.
• The posterior belly, which is longer than the anterior,
is attached in the mastoid notch of the temporal bone,
and passes downwards and forwards.
• The anterior belly is attached to the digastric fossa on
the base of the mandible near the midline, and slopes
downwards and backwards.
• The two bellies meet in an intermediate tendon which
runs in a fibrous sling attached to the body and greater
cornu of the hyoid bone and is sometimes lined by a
synovial sheath. The tendon perforates stylohyoid.

13. The posterior belly of the digastric
• Comes from the medial surface of the mastoid process,
• Attaches to the anterior belly of digastric by the
intermediate tendon which is tied down by a fascial sling
to the body of the hyoid.
• Arises from the 2nd branchial arch and is innervated by
cranial nerve VII, while the anterior belly is derived from
the 1st arch and receives its nerve supply from V3 (the
mandibular division of the trigeminal nerve).
• Is associated with the stylohyoid muscle which is also
innervated by cranial nerveVII.

14. Variations
• Digastric may lack the intermediate tendon
and is then attached midway along the
body of the mandible. The posterior belly
may be augmented by a slip from the
styloid process or arise wholly from it. The
anterior belly may cross the midline and it
is not uncommon for it to fuse with
mylohyoid.

15. Relations
• Superficial to digastric are
– Platysma ,
– *sternocleidomastoid, splenius capitis, longissimus capitis and stylohyoid,
– Passes deep to angle of mandible
– The mastoid process(most posteriorly)
– Between mastoid process & angle of mandible it is covered by parotid.
– In anterior triangle it is overlapped by submandibular salivary gland.
– It is crossed by the retromandibular vein.
Medial to the anterior belly.
-Mylohyoid is medial to the anterior belly.
Medial to the posterior belly.
-3 main vessels:
-Internal jugular vein,
-Internal carotid and
-External carotid arteries,
-3 cranial nerves:
-The accessory nerve, vagus and hypoglossal nerve,
-Two arteries(branches of external carotid) pass backwards & upwards &
medially deep to upper & lower bordes of posterior belly are
-Posterior auricular artery deep to upper border
-Occipital artery deep to lower border.
-Others: Hyoglossus ,superior oblique and rectus capitis lateralis, &
-The transverse process of the atlas vertebra,
.

19. 3 cranial nerves in relation to
posterior belly of digastric
• The vagus nerve runs vertically
downwards between internal jugular vein
& internal carotid artery
• The accessory nerve passes downwards
& backwards between posterior belly of
digastric & internal jugular vein
• The hypoglossal nerve passes between
posterior belly of digastric & internal
carotid artery

21. Vascular supply
• The posterior belly is supplied by the
posterior auricular and occipital arteries.
• The anterior belly of digastric receives its
blood supply chiefly from the submental
branch of the facial artery.

22. Innervation
• The anterior belly of digastric is supplied
by the mylohyoid branch of the inferior
alveolar nerve, and the posterior belly is
supplied by the facial nerve.
• The different innervation of the two parts
reflects their separate derivations from the
mesenchyme of the first and second
branchial arches.

23. Actions
• Digastric depresses the mandible and can
elevate the hyoid bone.
• The posterior bellies are especially active
during swallowing and chewing.

25. Relationships of the posterior belly of the digastric muscle
• 1) between the posterior belly of the digastric muscle
and the skin of the neck:
– The external jugular vein
– The cutaneous branches of great auricular nerve
– The cervical branch of VII
• 2) deep to the posterior belly of digastric
– The internal jugular vein
– The internal and external carotid arteries
– Cranial nerves X, XI, XII
• Deeper, cranial nerve IX and the sympathetic trunk
– The cranial nerve IX or glossopharyngeal nerve runs deep
to the internal carotid artery and penetrates the lateral
pharyngeal wall with the stylopharyngeus muscle. It is motor
to this muscle and sensory to the mucosa of posterior 1/3 of
tongue, mucosa of pharynx, palatine tonsil and soft palate.

27. Relations of the Internal Carotid Artery in the Neck
• Anterolaterally:
– Below the digastric lie the skin, the fascia, the anterior
border of the sternocleidomastoid, and the hypoglossal
nerve.
– Above the digastric lie the stylohyoid muscle, the
stylopharyngeus muscle, the glossopharyngeal nerve, the
pharyngeal branch of the vagus, the parotid gland, and the
external carotid artery.
• Posteriorly: The sympathetic trunk, the longus capitis
muscle, and the transverse processes of the upper
three cervical vertebrae
• Medially: The pharyngeal wall and the superior
laryngeal nerve
• Laterally: The internal jugular vein and the vagus
nerve

28. External carotid branches
• External carotid branches lie inferior to, deep to or superior to the
posterior belly of the digastric.
• Inferior to the posterior belly of the digastric:
1) The superior thyroid artery runs to the superior pole of the thyroid
gland, anastomoses with its opposite counterpart and the inferior thyroid
artery. Its branches are:
– The superior laryngeal artery running with the internal laryngeal nerve to
become internal laryngeal artery and nerve .
– The cricothyroid branch running with the external laryngeal nerve.
– The muscular branch to the sternocleidomastoid muscle.
2) The lingual artery supplies the tongue
3) The ascending pharyngeal artery (at the bifurcation of the common
carotid artery) supplies the lateral wall of the pharynx and the nasopharynx.
• Deep to the posterior belly of the digastric:
– The facial artery
– The occipital artery (lying superior to cranial nerve XII)
• Superior to the posterior belly of the digastric:
– The posterior auricular branch with its stylomastoid branch supplying cranial
nerve VII. Neuritis compresses the artery and leads to Bell's palsy.
– The maxillary artery
– The superficial temporal artery