Appendicular Muscles

triceps brachii

Large freshly muscle that is only muscle of posterior compartment of arm; origin - long head on infraglenoid tubercle, lateral and medial heads on posterior humerus; insertion - olecranon; action - powerful forearm extensor, prime mover, antagonist of forearm flexion; innervation - radial nerve

biceps brachii

Two-headed fusiform muscle of anterior arm; origin - short head on corocoid process, long head on supraglenoid tubercle and lip of glenoid cavity; insertion - radial tuberosity; action - flexes elbow joint and supinates forearm; innervation - musculocutaneous nerve

brachialis

Strong muscle immediately deep to biceps brachii on distal humerus; origin - front of distal humerus, embraces insertion of deltoid; insertion - coronoid process of ulna and capsule of elbow joint; action - major forearm flexor; innervation - musculocutaneous nerve

flexor carpi radialis

Runs diagonally across forearm; origin - medial epicondyle of humerus; insertion - base of second and thrid metacarpals, provides guide to position of radial artery at wrist for pulse; action - powerful flexor of wrist; abducts hand; innervation - median nerve

flexor digitorum superficialis

Two headed, more deeply placed muscle of superficial anterior forearm; origin - medial epicondyle of humerus, coronoid process of ulna, shaft of radius; insertion - middle phalanges of fingers 2-5; action - flexes wrist and middle phalanges of fingers 2-5; important flexor for speed against resistance; innervation - median nerve

extensor digitorum

Muscle of superficial posterior forearm; origin - lateral epicondyle of humerus; insertion - distal phalanges fingers 2-5; action - prime mover of finger extension; innervation - posterior interosseous nerve

extensor carpi ulnaris

Most medial of superficial posterior muscles of forearm; origin - lateral epicondyle of humerus and posterior border of ulna; insertion - base of fifth metacarpal; action - extends and adducts wrist; innervation - posterior interosseous nerve

iliacus

Large, fan-shaped more lateral muscle of composite of two closely related muscles; origin - iliac fossa and crest, ala of sacrum; insertion - lesser trochanter; action - prime mover for flexing thigh, or flexing trunk on thigh; innervation - femoral nerve

psoas major

Longer, thicker, more medial muscle of composite of two closely related muscles; tenderloin; origin - transverse processes, bodies and discs of lumber vertebrae and T₁₂; insertion - lesser trochanter; action - prime mover for flexing thigh, flexing trunk on thigh, or flexes vertebral column laterally; important postural muscle; innervation - ventral rami L₁-L₃

sartorius

Straplike superficial muscle running obliquely across anterior surface of thigh to knee; longest muscle in body; crosses both hip and knee joints; origin - anterior superior iliac spine; insertion - proximal medial tibia; action - flexes, abducts, and laterally rotates thigh; weak knee flexor; helps produce the cross-legged position; innervation - femoral nerve

adductor longus

Most anterior of adductor muscles in medial thigh compartment; origin - near pubic symphysis; insertion - linea aspera; action - adducts, flexes, and medially rotates thigh; innervation - obturator nerve

gracilis

Long, thin, superficial muscle of medial thigh; origin - inferior ramus and body of pubis and ischial ramus; insertion - medial tibia just inferior to medial condyle; action - adducts thigh, flexes and medially rotates leg, especially during walking; innervation - obturator nerve

rectus femoris

Superficial muscle of anterior thigh; runs straight down thigh; longest head and only muscle of group to cross hip joint; origin - anterior inferior iliac spine and superior margin of acetabulum; insertion - patella and tibial tuberosity; action - extends knee and flexes thigh at hip; innervation - femoral nerve

gluteus maximus

Largest and most superficial muscle forming bulk of buttocks; important site of intramuscular injection; overlies large sciatic nerve; covers ischial tuberosity only when standing; origin - dorsal ilium, sacrum, and coccyx; insertion - gluteal tuberosity and iliotibial tract; action - major extensor of thigh; powerful and most effective when thigh is flexed and force is necessary as in climbing stairs and running; laterally rotates and abducts thigh; innervation - inferior gluteal nerve

biceps femoris

Most lateral muscle of posterior compartment of thigh; origin - long head on ischial tuberosity and short head on linea aspera, lateral supracondylar line, and distal femur; insertion - fibula head and lateral condyle of tibia; action - extends thigh and flexes knee; laterally rotates leg, especially when knee is flexed; innervation - sciatic nerve, tibial to long head and common fibular to short head

tibialis anterior

Superior muscle of anterior lateral border of leg; origin - lateral condyle and upper 2/3 of tibial shaft and interosseous membrane; insertion - inferior surface of medial cuneiform and first metatarsal; action - prime mover of dorsiflexion, inverts foot, and helps support medial longitudinal arch of foot; innervation - deep fibular nerve

extensor digitorum longus

unipennate muscle on anterolateral surface of leg; origin - lateral condyle of tibia, proximal 3/4 of fibula, and interosseous membrane; insertion - middle and distal phalanges of toes 2-5; action - prime mover of toe extension and dorsiflexes foot; innervation - deep fibular nerve

gastrocnemius

Superficial of two muscles that shape posterior calf; origin - one head medial condyle of femur other head lateral condyle of femur; insertion - calcaneus; action - plantar flexes foot when knee is extended and flex knee when foot is dorsiflexed; innervation - tibial nerve

flexor digitorum longus

Long, narrow muscle of deep posterior leg compartment; origin - extensive on posterior tibia; insertion - distal phalanges toes 2-5; action - plantar flexes and inverts foot; flexes toes, helps foot grip ground; innervation - tibial nerve

flexor/extensor retinacula

Bandlike thickenings of deep fascia that securely anchor tendons and keep them from jumping around when tensed; located in arms for tendons running to hand and ankle for tendons running to foot