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

6. SUBMENTAL TRIANGLE It lies below the chin. Boundaries :
Anteriorly: midline of the neck.
Laterally: Anterior belly of Digastric.

7. BOUNDARIES
Inferiorly : body of the hyoid.
Floor: Mylohyoid muscle.

8. CONTENTS Submental lymph nodes.
They receive lymph from the tip of the tongue.

9. MYLOHYOID MUSCLE
It is a flat triangular sheet that supports the floor of the mouth and tongue (forms the main part of the floor of the mouth).
Origin :
Mylohyoid line of the mandible.

10. MYLOHYOID Insertion: The anterior fibers: Into a Fibrous Raphe.
The posterior fibers: Into the body of hyoid bone.

11. MYLOHYOID
Nerve supply :
Nerve to mylohyoid.

12. MYLOHYOID
Action :
If the mandible is fixed: Elevates the floor of the mouth as in deglutition.
If the hyoid bone is fixed: Depresses the mandible and opens the mouth.

13. DIGASTRIC TRIANGLE It lies below the body of the mandible. Boundaries:
Anteriorly:
Anterior belly of Digastric.
Posteriorly:
Posterior belly of digastric & Stylohyoid.

14. DIGASTRIC TRIANGLE Superiorly:
Lower border of the body of the mandible.
Floor:
Mylohyoid. Hyoglossus.

15. CONTENTS A. Anterior part : (1) Submandibular salivary gland.
(2) Facial artery (deep to gland).
(3) Facial vein
(4) Submandibular lymph nodes.
The vein and lymph nodes are superficial to the gland.

16. CONTENTS
(5) Hypoglossal nerve.
(6) Nerve and vessels to mylohyoid.

17. CONTENTS B. posterior part: 1. Carotid sheath and its contents.
2. parotid gland (Lower part)

18. DIGASTRIC MUSCLE It has two bellies: Anterior and Posterior.
Posterior belly :
Arises from the mastoid process.
Inserted into the intermediate tendon.
Anterior belly attached to the lower border of body of mandible.

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

20. NERVE SUPPLY Posterior belly: Facial Nerve Anterior belly:
The nerve to Mylohyoid.

21. ACTION
Depression of the mandible. OR
Elevation of the hyoid bone.

22. STYLOHYOID MUSCLE Origin: The styloid process.
It runs along the upper border of the posterior belly of digastric.
Insertion:
Hyoid bone (between body and greater horn).

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

24. CAROTID TRIANGLE It is behind the hyoid bone. Boundaries : Superiorly:
Posterior belly of Digastric.
Inferiorly:
Superior belly of Omohyoid.

25. BOUNDARIES Posteriorly: Anterior border of sternomastoid. Floor:
Thyrohyoid. Hyoglossus.
Middle & Inferior constrictors of the pharynx.

26. CONTENTS (1) Carotid sheath
(2) Hypoglossal nerve and its descending branch.
(3) Acessory nerve.

27. CONTENTS (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. CONTENTS 1. Common and internal carotid arteries.
2. Internal jugular vein.
3. Vagus nerve.
4. Deep cervical lymph nodes. They form a chain along the internal jugular vein.

30. CAROTID SHEATH It is crossed by Glossopharyngeal. Hypoglossal.
Spinal part of acessory.

31. MUSCULAR TRIANGLE It lies below the hyoid bone. Boundaries:
Anteriorly :
Midline of the neck.
Superiorly:
Superior belly of Omohyoid.

32. MUSCULAR TRIANGLE Inferiorly: Anterior border of Sternomastoid Floor:
Sternohyoid. Sternothyroid.

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

34. INFRAHYOID MUSCLES

35. ORIGIN Sternohyoid & Sternothyroid :
Posterior surface of the manubrium.
Thyrohyoid:
Oblique line of thyroid cartilage.

36. ORIGIN Omohyoid : Inferior belly :
Suprascapular ligament and Suprascapular notch.
Superior belly:
Intermediate tendon.

37. INSERTION Sternohyoid & Sternothyroid : Hyoid bone (lower border).
Oblique line of thyroid cartilage.
Thyrohyoid:

38. INSERTION
Omohyoid
Hyoid bone (lower border).

39. NERVE SUPPLY Ansa Cervicalis (C1,2&3) EXCEPT Thyrohyoid:
(C1) through the hypoglossal nerve.

40. ACTION
(1) stabilization of the hyoid bone to make a base for the movements of the tongue.
(2) Assistance in the movements of the larynx in swallowing.