**Question:** Muscle involved in the closing of jaw are all except

A. Masseter
B. Temporalis
C. Digastric
D. Styloideus

**Core Concept:**
The jaw, also known as the mandible, is a bony structure that forms the lower part of the face and is responsible for the movements required for chewing, speaking, and closing the mouth. The muscles involved in jaw movements are essential for understanding the pathophysiology and treatment of various disorders affecting the jaw.

**Why the Correct Answer is Right:**
The correct answer is "D. Styloideus" because the correct answer should be a muscle that is not involved in jaw closing. The styloideus muscle is a small, slender muscle that originates from the styloid process and inserts into the styloid process. It is not directly involved in jaw closing but rather contributes to the movements of the styloid process and stylomandibular ligament.

**Why Each Wrong Option is Incorrect:**

A. Masseter (Masseter muscle): This large, quadrilateral muscle is primarily responsible for the downward and medial movements of the mandible, which involves jaw closing. It originates from the zygomatic arch, runs medially and inferiorly, and inserts into the angle of the mandible.

B. Temporalis (Temporalis muscle): Another large, quadrilateral muscle, the temporalis muscle plays a crucial role in jaw closing and mandibular movements. It originates from the temporal fossa and inserts into the angle of the mandible.

C. Digastric (Digastric muscle): This muscle is involved in both the opening and closing of the jaw. It originates from the posterior border of the lower edge of the mandible and inserts into the mylohyoid muscle.

D. Styloideus (Styloideus muscle): As mentioned earlier, this muscle is not involved in jaw closing but plays a role in the movements of the styloid process and stylomandibular ligament.

E. Digastric (Digastric muscle): This muscle is involved in both the opening and closing of the jaw. It originates from the posterior border of the lower edge of the mandible and inserts into the mylohyoid muscle.

F. Mylohyoid (Mylohyoid muscle): This muscle plays a role in the movements of the hyoid and tongue. It originates from the mylohyoid ridge and inserts into the body of the hyoid bone. It is not directly involved in jaw closing but contributes to the opening and closing movements of the jaw via its connection to the hyoid bone, which is connected to the mandible.

G. Sternothyroid (Sternothyroid muscle): This muscle is responsible for raising the thyroid cartilage and thus indirectly contributes to jaw closing. It originates from the anterior two-thirds of the thyroid cartilage and inserts into the thyroid cartilage.

**Clinical Pearl:** The correct answer is C. Digastric muscle, as it plays a role in jaw movements and is involved in both jaw opening and closing. It originates from the posterior border of the lower edge of the mandible and