Ans. A (Ref: Gray-' $ 40/e p539} Both A & B helps in protrusion of jaw. But A>B Protrusion of jaw is tarried out by the bilateral action of lateral pterygoid muscle which is represented by *A' in the diagram, originating by two heads from sphenoid bone and getting inserted at anterior surface of mandibular condyle. Muscles Marked in the Diagram A * Lateral Pterygoid B * Medial Pterygoid C * Buccinator D * Pterygomandibular Raphe "Lateral pterygoid is a short, thick muscle consisting of two parts. The upper head arises from the infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone. The lower head arises from the lateral surface of the lateral pterygoid plate. From the two origins, the fibres converge, and pass backwards and laterally, to be inserted into a depression on the front of the neck of the mandible (the pterygoid fovea)." -- Gray's 40/e p539 "Actions of Lateral Pterygoid: When left and right muscles contract together the condyle is pulled forward and slightly downward. If only one lateral pterygoid contracts, the jaw rotates about a vertical axis passing roughly through the opposite condyle and is pulled medially toward the opposite side. This contraction together with that of the adjacent medial pterygoid (both attached to the lateral pterygoid plate) provides most of the strong medially directed component of the force used when grinding food between teeth of the same side. It is arguably the most importantfunction of the inferior head of lateral pterygoid. " -- Grays 40/e p5 39. Movements of Mandible Protrusion Retraction Depression Elevation Side to side * Lateral pterygoidQ * Medial pterygoidQ * Posterior fibers of temporalis * Lateral pterygoidQ * DigastricQ * GeniohyoidQ * MylohyoidQ * MasseterQ * Medial pterygoidQ * TemporalisQ * Lateral pterygoidQ * Medial pterygoidQ Muscles of Mastication Muscle Origin Insertion Actions Masseter * Maxillary process of the zygomatic boneQ * Anterior two-thirds of inferior border of zygomatic archQ * Angle & lower posterior half of lateral surface of mandibular ramusQ * Elevation of mandible * Small effect in side-to-side movements, protraction & retractionQ Temporalis * Temporal fossa & deep surface of the temporal fasciaQ * Medial surface, apex, anterior & posterior borders of coronoid process * Anterior border of mandibular ramusQ * Elevation of mandibleQ Medial pterygoid * Deep head arises from medial surface of lateral pterygoid plate of sphenoid boneQ * Superficial head arises from maxillary tuberosity & pyramidal process of palatine boneQ * Medial surface of ramus & angle of mandibleQ * Elevation, protrusion & side-to-side movement of mandibleQ Lateral pterygoid * Upper head arises from infratemporal surface & infratemporal crest of greater wing of sphenoid boneQ * Lower head arises from lateral surface of lateral pterygoid plateQ * Front of the neck of the mandibleQ (the pterygoid fovea) * Depression, protrusion & side-to-side movement of mandibleQ