Appendix D · Muscle Reference Tables

This is the origin, insertion, action, and innervation reference that Chapter 10 points to. It is long, and it is not meant to be read from front to back. It is meant to be used — and used in a particular way, which the first section explains.

D.1 How to Use a Muscle Table

Students who memorize these tables row by row learn about six hundred facts, forget them within a semester, and cannot answer a question phrased any differently. Students who learn four principles derive most of the table on demand and keep it for years. The principles are worth the twenty minutes.

Principle 1 · The action follows from the geometry

A muscle can do exactly one thing: shorten, pulling its insertion toward its origin. Everything else — flexion, extension, abduction, rotation — is a consequence of where the line of pull sits relative to the joint's axis of rotation.

A muscle crossing anterior to a transverse axis flexes the joint. One crossing posterior extends it. One crossing lateral to an anteroposterior axis abducts. One crossing medial adducts. One whose line of pull spirals around a longitudinal axis rotates.

Three derivations, done before reading the answer.

• Biceps brachii runs from the scapula to the radial tuberosity, passing anterior to the elbow's transverse axis and attaching to the radius somewhat medially. Anterior to a transverse axis means flexion. Attaching to the radius, which rotates, means it can also supinate — and because the radial tuberosity faces posteromedially in pronation, the biceps is a powerful supinator, which is why right-handed screw threads tighten clockwise. Prediction confirmed.
• Gluteus medius runs from the outer surface of the ilium to the greater trochanter, passing lateral to the hip's anteroposterior axis. Lateral to an AP axis means abduction. And because it works on a limb that is often fixed to the ground, its more important job is the reverse action: holding the pelvis level while the opposite foot is off the ground.
• Tibialis anterior runs down the front of the leg and crosses anterior to the ankle's transverse axis, then attaches to the medial side of the foot at the medial cuneiform. Anterior means dorsiflexion; medial attachment means inversion. It does both.

You did not memorize any of that. You derived it. Figure D.1 makes the rule visual, and Appendix C §C.7 develops the movement vocabulary.

Principle 2 · The name usually tells you the answer

Muscle names are descriptions, and once you can read them, most of the table is redundant.

Flexor digitorum profundus is a complete sentence: it flexes, it acts on the digits, and it is the deep one — which tells you there is a superficial one, and that the deep tendon must pass through the superficial one to reach further along the finger. It does, and that arrangement is why flexor digitorum superficialis flexes the middle phalanx while profundus flexes the distal.

Principle 3 · Learn by compartment and by nerve, not alphabetically

The compartment is the unit that fails clinically. A fascial compartment contains a group of muscles with a shared action, supplied by one nerve and one artery, inside one inextensible fibrous box. Learn "anterior compartment of the leg: four muscles, deep fibular nerve, anterior tibial artery, dorsiflexion and toe extension" and you have acquired twelve facts in one sentence, along with the reason a lesion at the fibular neck produces foot drop and nothing else.

§D.16 gives the whole compartment-and-nerve summary in one table. If you learn nothing else from this appendix, learn that table.

Principle 4 · Origin and insertion are a convention that reverses

By convention the origin is the more proximal or less mobile attachment and the insertion the more distal or more mobile one. That convention describes the open-chain action, with the distal segment free. In real movement the distal segment is often fixed to the ground or to a bar, and the muscle then moves the origin toward the insertion instead — the reverse or closed-chain action.

• Psoas major runs from the lumbar vertebrae to the lesser trochanter. Open chain, standing, it flexes the hip. Closed chain, lying down with the feet held, it flexes the trunk — which is why a sit-up is substantially a psoas exercise and why psoas tightness contributes to lumbar lordosis.
• Latissimus dorsi runs from the lower spine and iliac crest to the humerus. Open chain it extends and adducts the arm. Closed chain, with the hands fixed on a bar, it lifts the trunk toward the arm — the pull-up.

Alongside this, four functional roles you will meet constantly: the agonist (prime mover) produces the action; the antagonist opposes it and controls it eccentrically; the synergist assists or eliminates unwanted secondary actions; the fixator stabilizes the origin so the agonist has something to pull against. The rotator cuff spends most of its working life as a set of fixators, not as prime movers.

One more thing: segmental innervation does not follow adult position

A muscle keeps the spinal nerve supply of the segment it developed from, no matter where it migrates to. The diaphragm develops in the cervical region as the septum transversum and descends through the thorax during weeks 4 to 8, dragging its nerve behind it — which is why a muscle sitting at the T8–T12 level is supplied by C3, C4, and C5, and why irritation of the diaphragm (blood under it, gallbladder inflammation) refers pain to the shoulder tip, which shares those segments (Chapters 22 and 28).

     CROSS-SECTION OF THE MID-LEG — WHY THE COMPARTMENT IS THE UNIT

                              ANTERIOR
                    ┌───────────────────────────┐
                    │  ANTERIOR COMPARTMENT     │
                    │  tibialis anterior        │
                    │  ext. digitorum longus    │   nerve: DEEP FIBULAR
                    │  ext. hallucis longus     │   artery: ANTERIOR TIBIAL
                    │  fibularis tertius        │   action: DORSIFLEXION
              ╔═════╧═══╗                 ╭─────╯            + toe extension
              ║  TIBIA  ║   interosseous  │
              ║         ║   membrane      │  ┌──────────────────────────┐
              ╚═════╤═══╝ ════════════════╪══│ LATERAL COMPARTMENT      │
   MEDIAL           │                  ╔══╧═╗│ fibularis longus         │ LATERAL
     ◄──────        │                  ║FIB-║│ fibularis brevis         │ ──────►
                    │                  ║ULA ║│ nerve: SUPERFICIAL FIB.  │
              ┌─────┴──────────────╮   ╚══╤═╝│ action: EVERSION         │
              │ DEEP POSTERIOR      │      │  └──────────────────────────┘
              │ COMPARTMENT         │      │
              │ tibialis posterior  │      │   COMMON FIBULAR NERVE splits
              │ flexor dig. longus  │      │   at the FIBULAR NECK  ▲
              │ flexor hall. longus │      │   into deep + superficial
              │ popliteus           │      │   ── most superficial major
              │ nerve: TIBIAL       │      │      nerve in the body ──
              │ artery: POST. TIBIAL│      │
              │        + FIBULAR    │      │
              └─────┬───────────────╯      │
                    │                      │
              ┌─────┴──────────────────────┴───────┐
              │  SUPERFICIAL POSTERIOR COMPARTMENT │
              │  gastrocnemius · soleus · plantaris│
              │  nerve: TIBIAL                     │
              │  action: PLANTARFLEXION            │
              └────────────────────────────────────┘
                              POSTERIOR

   ═══════════════════════════════════════════════════════════════════
   ONE FASCIAL BOX = one nerve + one artery + one shared action.
   Cut the nerve → the whole box fails together, and the antagonist
   compartment, now unopposed, holds the joint in its own direction.
   Deep fibular nerve cut →  no dorsiflexion → FOOT DROP, foot held
                             plantarflexed by the intact calf.

D.2 Muscles of Facial Expression

These muscles are unique in inserting into skin rather than bone, which is what allows them to move the face rather than the skeleton. All are derived from the second pharyngeal arch and all are supplied by the facial nerve (CN VII) — a fact worth stating once, because it means a single nerve lesion paralyzes the entire half-face.

D.3 Muscles of Mastication and the Hyoid

The four muscles of mastication derive from the first pharyngeal arch and are supplied by the mandibular division of the trigeminal nerve (CN V3). The hyoid muscles have a famously mixed supply, which is worth noticing rather than memorizing: they are assembled from several developmental sources.

The mechanism of swallowing in one line: the suprahyoid muscles pull the hyoid and larynx up and forward, which drags the epiglottis down over the laryngeal inlet and opens the upper esophageal sphincter; the infrahyoid muscles then pull them back down. Palpate your own larynx while swallowing and you will feel exactly this excursion (Chapter 23).

D.4 Muscles of the Tongue and Pharynx

All extrinsic and intrinsic tongue muscles are supplied by the hypoglossal nerve (CN XII) except palatoglossus; all pharyngeal muscles are supplied by the vagus (CN X) via the pharyngeal plexus except stylopharyngeus. The three exceptions in this table are examined constantly, precisely because they are exceptions.

Tongue deviation, explained. Genioglossus protrudes the tongue by pulling its root forward. If one hypoglossal nerve is damaged, that side cannot push, so the intact side pushes the tongue across — and the tongue deviates toward the side of the lesion. Two muscles pushing against each other, one of them switched off: the tongue goes where the push is weaker.

D.5 Muscles Moving the Head and Neck

Why sternocleidomastoid turns the face the other way. It runs from the front of the chest to behind the ear. Pulling the mastoid process forward and down swings the back of the skull toward the same shoulder, which necessarily swings the face away. Trace the line of pull with a finger on your own neck and the geometry is obvious. This is Principle 1 in a single muscle.

D.6 Muscles of the Vertebral Column

The deep back muscles are supplied by the posterior rami of the spinal nerves — without exception. This is the defining feature of true back muscles, and it distinguishes them from the superficial muscles (trapezius, latissimus, rhomboids) that migrated onto the back and kept their anterior-ramus supply.

Thoracolumbar fascia is the sheet the erector spinae arises from and lies within. It is continuous laterally with the aponeuroses of transversus abdominis and internal oblique, which means the abdominal wall can tension the fascia and thereby stiffen the lumbar spine. This is the anatomical basis of "core stability": the abdominal muscles brace the spine through a fascial connection, not by pulling on it directly (Chapter 10).

D.7 Muscles of Respiration

Quiet expiration uses no muscles at all. It is passive elastic recoil of the lung and chest wall, returning stored energy from inspiration. Muscular effort is required only for forced expiration — which is why a patient with severe airflow obstruction, who must actively force air out, becomes exhausted in a way that a patient with hypoxemia alone does not (Chapter 22).

D.8 Muscles of the Abdominal Wall and Pelvic Floor

The rectus sheath and the arcuate line. The aponeuroses of the three flat muscles wrap the rectus abdominis to form its sheath — but the arrangement changes partway down. Above the arcuate line (about midway between umbilicus and pubis), the internal oblique aponeurosis splits to pass both in front of and behind the rectus, so the muscle has a complete sheath. Below the arcuate line, all three aponeuroses pass anterior to the rectus, leaving only transversalis fascia behind it. That is why the inferior epigastric vessels enter the sheath at this level and why a low midline incision behaves differently from a high one.

D.9 Muscles of the Pectoral Girdle

These muscles move the scapula and clavicle, not the humerus. The scapula floats on the thorax with no bony articulation except the small acromioclavicular joint, so its position is entirely muscular — and that is what allows the shoulder its extraordinary range.

Winged scapula. Serratus anterior holds the medial border of the scapula flat against the ribs. Injure the long thoracic nerve — a superficial nerve, vulnerable in axillary surgery, in mastectomy, and to blunt trauma to the side of the chest — and that border lifts away from the thorax, standing out like a wing, most obviously when the patient pushes against a wall. The same lesion abolishes upward rotation, so the patient cannot raise the arm above the horizontal at all.

D.10 Muscles Moving the Arm at the Shoulder Joint

D.11 Muscles of the Arm and Forearm

Arm — anterior (flexor) compartment · musculocutaneous nerve

Arm — posterior (extensor) compartment · radial nerve

Forearm — anterior compartment, superficial layer

All arise wholly or partly from the common flexor origin on the medial epicondyle.

Forearm — anterior compartment, deep layer

Forearm — posterior compartment, superficial layer

All arise from or near the common extensor origin on the lateral epicondyle.

Forearm — posterior compartment, deep layer

D.12 Intrinsic Muscles of the Hand

D.13 Muscles Moving the Thigh

Gluteal region

Iliopsoas

Medial (adductor) compartment · obturator nerve

The adductor hiatus. The tendinous insertion of adductor magnus leaves a gap just above the adductor tubercle. The femoral artery and vein pass through it from the front of the thigh to the back, and change their names to popliteal artery and vein as they do. The muscle's anatomy names the vessel (see Appendix E).

D.14 Muscles of the Thigh

Anterior compartment · femoral nerve

Posterior compartment · the hamstrings

D.15 Muscles of the Leg and Foot

Leg — anterior compartment · deep fibular nerve · anterior tibial artery

Leg — lateral compartment · superficial fibular nerve

Leg — posterior compartment, superficial · tibial nerve

Leg — posterior compartment, deep · tibial nerve

The order of structures behind the medial malleolus, from front to back, is Tibialis posterior, flexor Digitorum longus, posterior tibial Artery, tibial Nerve, flexor Hallucis longus — and knowing it tells you what is compressed in tarsal tunnel syndrome and where to find the posterior tibial pulse.

Intrinsic muscles of the foot

The dorsal muscles are supplied by the deep fibular nerve; every plantar muscle is supplied by the medial or lateral plantar nerve, both branches of the tibial nerve. The plantar muscles are conventionally described in four layers from superficial to deep, and their function as a group is not to move the toes much but to stiffen the foot into a rigid lever during push-off and to control the arches.

Note the axis change between hand and foot: in the hand, abduction and adduction are referenced to the third digit; in the foot, to the second. That is why the dorsal interossei insert on both sides of digit 2 in the foot and on both sides of digit 3 in the hand.

D.16 Compartment and Nerve Summary

This is the table to learn if you learn only one. It is how clinical deficits actually present: not as "the flexor carpi ulnaris is weak," but as "the whole flexor compartment is weak, and the sensory loss follows the same nerve."

How compartment lesions actually present

• Foot drop — the common fibular nerve winds around the neck of the fibula covered by little more than skin. A tight plaster cast, a prolonged squat, habitual leg crossing, or a fibular neck fracture compresses it, and the anterior and lateral compartments fail together. The patient cannot dorsiflex, so the toes catch on the floor, and they compensate with a high-stepping gait.
• Wrist drop — the radial nerve lies directly against the humerus in the spiral groove. A mid-shaft humeral fracture or falling asleep with the arm over a chair back ("Saturday night palsy") paralyzes the extensor compartment. The wrist and fingers drop, but the triceps is spared, because its branches leave the nerve before the groove.
• Claw hand and hand of benediction — the two hand deformities look similar and mean opposite things. The claw is an ulnar lesion, present at rest. The benediction posture is a median lesion, visible only when the patient tries to make a fist.
• Winged scapula — long thoracic nerve, serratus anterior.
• Trendelenburg sign — superior gluteal nerve, gluteus medius and minimus. Ask the patient to stand on one leg: if the pelvis drops on the opposite side, the abductors of the standing leg have failed.

D.17 Self-Test

Predict before you look. Six of these give you attachments and ask for an action; four give you a deficit and ask for the nerve.

1. A muscle runs from the ischial tuberosity to the medial surface of the proximal tibia. Name its two actions.
2. A muscle runs from the lateral epicondyle of the humerus to the base of the fifth metacarpal. What are its two actions, and why two?
3. A muscle runs from the anterior surface of the sacrum to the superior border of the greater trochanter. What does it do to an extended hip, and what does it do to a flexed one?
4. A muscle runs from the coracoid process to the medial shaft of the humerus. Predict its actions.
5. A muscle runs from the posterior fibula to the distal phalanx of the great toe. Predict its action and name its compartment.
6. A muscle runs from the lateral femoral condyle to the posterior proximal tibia. Predict its action.
7. A patient cannot extend the wrist or fingers, and has numbness over the first dorsal web space of the hand. Name the nerve and the likely site.
8. A patient's scapula lifts away from the chest wall when they push against a wall.
9. A patient's pelvis drops on the left when they stand on the right leg.
10. A patient cannot dorsiflex the right foot, has normal eversion, and has numbness confined to the web space between the first and second toes.

Use this appendix with Appendix C §C.7 for the movement vocabulary and with Appendix E for the plexuses that supply every nerve named here.