1. ANTERIOR TRIANGLE
It is in front of the sternomastoid muscle.

2. BOUNDARIES Anteriorly: midline of the neck.
Posteriorly: anterior border of sternomastoid.
Superiorly: lower margin of the body of the mandible.

3. BOUNDARIES
Roof:
skin, superficial fascia (containing platysma) and the Investing layer of deep cervical fascia.

4. SUBDIVISIONS The anterior triangle is subdivided by :
The anterior and posterior bellies of the digastric and
The superior belly of omohyoid into (4) smaller triangles:

5. SUBDIVISIONS
Submental.
Submandibular (Digastric).
Carotid.
Muscular

6. DIGASTRIC MUSCLE The muscle has two bellies: Anterior and Posterior.
The posterior belly : arises from the mastoid process and inserted into the intermediate tendon.
The anterior belly attached to the lower border of body of mandible.

7. DIGASTRIC MUSCLE Intermediate tendon :
It pierces the insertion of stylohyoid.
It binds to the hyoid bone by a loop of deep fascia.

8. DIGASTRIC MUSCLE Nerve supply :
The facial nerve supplies the posterior belly.
The nerve to mylohyoid supplies the anterior belly.

9. DIGASTRIC MUSCLE Action : Depression of the mandible OR
Elevation of the hyoid bone.

10. STYLOHYOID It originates from the styloid process.
It runs along the upper border of the posterior belly of digastric.
It is inserted into the hyoid bone (between body and greater horn).

11. STYLOHYOID Nerve supply : Facial nerve. Action :
Elevation of hyoid bone.

12. SUBMENTAL TRIANGLE It lies below the chin. Its boundaries are:
Anteriorly: midline of the neck.
Laterally: anterior belly of digastric.

13. SUBMENTAL TRIANGLE Inferiorly : body of the hyoid.
Floor: mylohyoid muscle.

14. MYLOHYOID
It is a flat triangular sheet that supports the floor of the mouth and tongue.
It takes origin from the mylohyoid line of the mandible.

15. MYLOHYOID
Insertion:
The anterior fibers are inserted into a fibrous raphe.
The posterior fibers are inserted into the body of hyoid bone.

16. MYLOHYOID Nerve supply :
It is supplied by the nerve to mylohyoid (from inferior alveolar of mandibular).

17. MYLOHYOID
Action :
If the mandible is fixed, it elevates the floor of the mouth as in deglutition.
If the hyoid bone is fixed, it depresses the mandible and opens the mouth.

18. SUBMENTAL TRIANGLE Contents : Submental lymph nodes.
They receive lymph from the tip of the tongue.

19. DIGASTRIC TRIANGLE It lies below the body of the mandible.
It is bounded by:
Anteriorly: anterior belly of digastric.
Posteriorly: posterior belly of digastric and stylohyoid.

20. DIGASTRIC TRIANGLE Superiorly:
lower border of the body of the mandible.
Floor:
mylohyoid and hyoglossus muscles.

21. DIGASTRIC TRIANGLE Contents: A. Anterior part :
(1) Submandibular salivary gland.
(2) Facial artery (deep to gland).
(3) Facial vein
(4) submandibular lymph nodes (both superficial to gland).

22. DIGASTRIC TRIANGLE (5) Hypoglossal nerve.
(6) Nerve and vessels to mylohyoid.

23. DIGASTRIC TRIANGLE B. posterior part:
1. Carotid sheath (carotid arteries internal jugular vein and vagus nerve).
2. Lower part of the parotid gland.

24. CAROTID TRIANGLE It lies behind the hyoid bone. It is bounded by:
Superiorly:
posterior belly of digastric.
Inferiorly: superior belly of omohyoid.

25. CAROTID TRIANGLE Posteriorly: anterior border of sternomastoid. Floor:
thyrohyoid, hyoglossus,
middle and inferior constrictors of the pharynx.

26. CAROTID TRIANGLE Contents: (1) Carotid sheath and its contents.
(2) Hypoglossal nerve and its descending branch.
(3) Acessory nerve.

27. CAROTID TRIANGLE (4) Internal and External laryngeal nerves.
(5) Deep cervical lymph nodes.

28. CAROTID SHEATH It is a condensation of deep cervical fascia.
It is attached to the base of the skull superiorly and fuses with the pericardium inferiorly.

29. CAROTID SHEATH Contents : 1. Common and internal carotid arteries.
2. Internal jugular vein.
3. Vagus nerve.
4. Deep cervical lymph nodes form a chain along the internal jugular vein.

30. CAROTID SHEATH It is crossed by the following nerves:
Glossopharyngeal.
Hypoglossal.
Spinal part of acessory.

31. MUSCULAR TRIANGLE It lies below the hyoid bone. It is bounded by:
Anteriorly :
midline of the neck.
Superiorly:
superior belly of omohyoid.

32. MUSCULAR TRIANGLE Inferiorly: anterior border of sternomastoid Floor:
sternohyoid and sternothyroid muscles.

33. MUSCULAR TRIANGLE Beneath the floor lie: Thyroid gland. Larynx.
Trachea.
Esophagus.

34. INFRAHYOID MUSCLES They are thin, strap like muscles.
They are composed of
Sternohyoid.
Sternothyroid.
Thyrohyoid.
Omohyoid.

35. INFRAHYOID MUSCLES Action :
(1) stabilization of the hyoid bone to make a base for the movements of the tongue.
(2) Assist in the movements of the larynx in swallowing.

36. INFRA HYOID MUSCLES Nerve supply :
All are supplied by the ansa cervicalis (C1,2&3) except
Thyrohyoid (supplied by C1 through the hypoglossal nerve).

37. INFRA HYOID MUSCLES Origin : Sternohyoid & Sternothyroid :
posterior surface of the manubrium.
Insertion :
Hyoid bone (lower border).
Oblique line of thyroid cartilage.

38. INFRA HYOID MUSCLES Thyrohyoid : Origin :
oblique line of thyroid cartilage.
Insertion :
hyoid bone (lower border).

39. INFRA HYOID MUSCLES Omohyoid : Inferior belly :
Origin : suprascapular ligament and suprascapular notch.
Superior belly:
Origin :
intermediate tendon.
Insertion : hyoid bone (lower border).