Extension: increasing the angle between two bones (straightening a bend). The triceps brachii and anconeus are muscles that extend the elbow. The biceps brachii, brachialis, and brachioradialis flex the elbow. The gluteus medius, gluteus minimus, tensor fasciae latae, and sartorius are muscles that abduct the hip.

An extensor muscle is located on the back of the upper arm. An extensor muscle is a muscle that works to extend or straighten a body part, effectively enlarging the angle between body parts. Examples of extensor muscles include the muscles that straighten the elbow or the knee.

There are four muscles in the anterior compartment of the leg: tibialis anterior, extensor digitorum longus, extensor hallucis longus and fibularis tertius….Extensor Hallucis Longus

• Attachments: Originates from the medial surface of the fibular shaft.
• Action: Extension of the great toe and dorsiflexion of the foot.

The posterior compartment of the forearm (or extensor compartment) contains twelve muscles which are chiefly responsible for extension of the wrist and digits, and supination of the forearm. It is separated from the anterior compartment by the interosseous membrane between the radius and ulna.

Despite the bulk of the muscle body being visible from the anterior aspect of the forearm, the brachioradialis is a posterior compartment muscle and consequently is innervated by the radial nerve.

Anterior and Posterior Anterior refers to the ‘front’, and posterior refers to the ‘back’.

Posterior or dorsal – back (example, the shoulder blades are located on the posterior side of the body). Medial – toward the midline of the body (example, the middle toe is located at the medial side of the foot).

Posterior comes from the Latin word posterus, meaning “coming after”. Posterior is often used as a technical term in biology and medicine to refer to the back side of things, and is the opposite of anterior, which refers to the front side.

Coronal plane – a vertical line which divides the body into a front (anterior) section and back (posterior) section.

Sagittal plane – a vertical plane that divides the body into left and right sides. Flexion and extension types of movement occur in this plane, eg kicking a football, chest pass in netball, walking, jumping, squatting.

Anatomical Planes of the Body

Sagittal Plane: A Sagittal Plane divides the body into right/left parts [head, neck, trunk, tail].

A coronal or frontal plane divides the body into dorsal and ventral (back and front, or posterior and anterior) portions. A transverse plane, also known as an axial plane or cross-section, divides the body into cranial and caudal (head and tail) portions.

The nine divisions are part of parasagittal and two transverse planes of body-centered around the navel. These divisions are important anatomically to determine the location of the organ within the abdomen and pelvic area.