Abductor Muscles

Abduction refers to movement of a limb away from the central line of the body or of a digit away from the axis of a limb. Muscles, then, that carry out this type of movement are called "abductor muscles."

Adductor Muscles

Adductor muscles move a limb toward the central line of the body or a digit toward the axis of a limb. It comes from the Latin word, "adductus," meaning "one that draws to". An adductor is also a muscle that closes the valves in a clam or other bivalve mollusk, but it isn't the one that snaps the human mouth shut.

Carpal Bones

The skeleton of the wrist consists of eight small "carpal bones" that are firmly bound in two rows of four bones each. The resulting mass is the "carpus." The eight bones are the "pisiform," "triangular" or "triquetrum," the "pisiform," "lunate," and "scaphoid" on the upper end of the wrist, where it connects with ligaments and the lower arm bones, and the "hamate," "capitate," "trapezoid," and "trapezium" on the lower side of the hand by the "metacarpals," or first joint of the fingers.

Joints in the Hand

The joints where the phalanges attach to the metacarpal joints are called the metacarpophalangeal (MCP) joints. The joints between the proximal and middle segments are the proximal interphalangeal (PIP) joints and the segments between the middle and distal segments are the distal interphalangeal joints.

Fibrous Sheath

The digital synovial sheath is a membranous sheath enclosing the flexor tendons and serve to prevent bowstringing of the tendons during flexion.

Phalanges

The phalanges are the small bones that make up the skeleton of the fingers, thumb and toes. Each finger and smaller toe has three phalanges; the thumb and big toe each have two. The phalange nearest the body of the hand or foot is call the "proximal" phalange; the one at the end of each digit is the "distal" phalange; and, of course, when there are three, the middle one is called the "middle" phalange.

Extensor Carpi Radialis Brevis

The extensor carpi radialis brevis is a companion of the extensor carpi radialis longus and extends toward the middle of it. This muscle runs from the humerus (upper arm bone) to the bones in the hand and functions to extend the wrist. It also assists in abducting the hand.

Extensor Carpi Ulnaris

The extensor carpi ulnaris is located along the outer surface of the ulna (longer forearm bone) and connects the humerus (upper arm bone) to the hand. It acts to extend the wrist and assists in abducting it.

Extensor Muscles

Muscle extension occurs when the angle between the bones is increased - as when the forearm is aligned with the arm. An "extensor", then, is any muscle serving to extend a bodily part (usually a limb) away from the body or when a digit is extended from its base.

Dorsal Flexors

A number of muscles that function to move the ankle, foot, and toes are located in the lower leg. They attach the femur (upper leg bone), tibia, and fibula (lower leg bones) and to various bones in the foot and are responsible for a variety of movements - moving the foot upward (dorsiflexion) or downward (plantar flexion), and turning the sole of the foot inward (inversion) or outward (eversion). The "dorsal flexor muscles" include the following: The "tibialis anterior" is a dorsal flexor and is an elongated, spindle-shaped muscle located on the front of the lower leg. It arises from the surface of the tibia to pass on the inside over the far end of the tibia, and attaches to bones of the ankle and foot. Contraction of the tibialis anterior causes dorsiflexion and inversion of the foot. The tibialis posterior muscle helps stabilize the foot while walking. The "peroneus tertius" is a muscle of variable size that connects the fibula to the outside of the foot. It functions in dorsiflexion and eversion of the foot. The"extensor digitorum longus" is situated along the outside of the lower leg, just behind the tibialis anterior. It comes from close to the midline of the tibia and the shaft of the fibula. Its tendon divides into four parts as it passes over the front of the ankle. These parts continue over the surface of the foot and attach to the four smaller toes. The actions of this muscle include dorsiflexion of the foot, eversion of the foot, and extension of the toes.

Extensor Indicis

The extensor indicis muscle (not tendon) extends the index finger.

Extensor Retinaculum

A structure called the "extensor retinacula" consists of a group of heavy connective fibers in the tissues of the wrist. It connects the lateral margin of the radius (shorter forearm bone) with the inside border of the ulna (longer forearm bone) and with certain bones of the wrist. The retinaculum gives off branches of connective tissue to the underlying wrist bones, creating a series of sheath-like compartments through which the tendons of the extensor muscles pass to the wrist and fingers. As in the case of the wrist, the tissue formations in various regions of the ankle is thickened to form retinacula. Toward the front, for example, extensor retinacula connect the tibia and fibula (lower leg bones) as well as the calcaneus (Achilles tendon) and tissue of the sole of the foot. These retinacula form sheaths for tendons crossing the front of the ankle.

Flexor Digitorum Profundis

The flexor digitorum profundis is a large muscle that connects the ulna (longest forearm bone) to the bones of the fingers. It acts to flex the distal joints of the fingers, as when a fist is made.

Condyles of The Humerus

At the lower end of the humerus (upper arm bone) and the femur, there are two smooth condyles (rounded processes of the bone): a knob-like "capitulum" on the lateral side and a pulley-shaped "trochlea" in the middle. The capitulum unites with the radius (smaller lower arm bone) at the elbow, and the trochlea is a notch which joins ligaments to the head of the ulna (larger lower arm bone). Above the condyles on either side are "epicondyles," which provide attachments for muscles and ligaments of the elbow. The one toward the center of the arm is the "medial epicondyle," and the one to the side is the "lateral epicondyle."

Lumbrical Muscles

The lumbrical muscles are four small, fleshy muscles that are associated with tendons between the four small toes of the foot and the four fingers of the hand. Each lumbrical muscle flexes the corresponding digital joint to extend the finger or toe in question.

Metacarpal

The metacarpal is one of five, long cylindrical bones in the body of the hand. The bones run from the carpal bones of the wrist to the base of each digit of the hand. On the palm of the hand, these are padded by a thick layer of fibrous, connective tissue; on the back of the hand, they can be seen and felt through the skin. The heads of the metacarpal bones form the knuckles.

Opponens Pollicis

The opponens pollicis muscle flexes and adducts the thumb.

Palmar Interosseous

The palmar interosseous muscles are adductors of the digits in the hand.

Ligaments of The Hand and Wrist

On the radial shaft of the smaller forearm bone, just below its head, is a process called the "radial tuberosity." It serves to attach the biceps brachi muscle, which bends the arm at the elbow. At the lower end of the radius, a lateral "styloid process" provides attachments for the "palmar radiocarpal ligament" (on the palm of the hand) and the "dorsal radiocarpal ligament" (on the back of the hand) from the radius into the wrist. At the lower end of the larger forearm bone (ulna), its knob-like head articulates with a notch of the radius (ulnar notch) laterally and with a disk of fibrocartilage below. This disk, in turn, joins a wrist bone (the triquetrum). A medial "styloid process" at the lower end of the ulna provides attachments for ligaments ("palmar ulnocarpal ligament" and "dorsal ulnocarpal ligament") into the wrist. The skeleton of the wrist is made up of eight small "carpal bones" that are firmly bound in two rows of four bones each. The mass that results from these bones is called the "carpus." The carpus is rounded on its nearest surface, where it articulates with the radius and with the fibrocartilaginous disk on the ulnar side. The carpus is rounded convexly in the front, forming a canal (retinaculum) through which tendons, ligaments and nerves extend to the palm. Its distal surface articulates with the metacarpal bones, which are joined to the carpus by the "palmar carpometacarpal ligaments."