CorpusHuman Anatomy

Muscles — Posterior View

Superficial layer (body’s left) and deep layer (body’s right)

Posterior view of the whole body in the anatomical position. The left half of the image (the body's left side) shows the superficial muscles: trapezius, deltoid, latissimus dorsi, triceps, the forearm extensors, gluteus maximus, the hamstrings and the triceps surae. The right half shows the next layer after these have been removed. You can see the scapular stabilisers (levator scapulae, rhomboids) and the posterior rotator cuff on the scapula, the erector spinae columns, the deep forearm "outcropping" muscles, gluteus medius with piriformis and the short lateral rotators, the sciatic nerve emerging below piriformis, and soleus, popliteus and plantaris in the calf.

Note how fibre direction reflects action: trapezius fibres converge on the spine of the scapula, latissimus sweeps up into the axilla, gluteus maximus runs inferolaterally into the iliotibial tract, and the two gastrocnemius heads enclose the popliteal fossa with the hamstring tendons. A gentle pulse runs down the major prime movers. Hover or tap any muscle to open its entry.

Step-by-step

  1. Superficial back and shoulder

    Trapezius (CN XI) suspends and rotates the scapula. Latissimus dorsi (thoracodorsal nerve) extends, adducts and medially rotates the arm. Deltoid (axillary nerve) caps the shoulder and abducts it from 15° to 90°.

  2. Scapular stabilisers

    Deep to trapezius, levator scapulae and the rhomboids (dorsal scapular nerve, C4–C5) elevate, retract and downwardly rotate the scapula, holding it against the chest wall together with serratus anterior (long thoracic nerve).

  3. Posterior rotator cuff

    Supraspinatus initiates abduction. Infraspinatus and teres minor laterally rotate the arm and hold the humeral head in the glenoid. Teres major, which is not part of the cuff, is "lat's little helper". The quadrangular and triangular spaces lie between teres minor, teres major and the long head of triceps.

  4. Intrinsic back muscles

    Erector spinae (iliocostalis, longissimus, spinalis: "I Love Spaghetti") and splenius are supplied segmentally by dorsal rami. They extend the spine and head and control forward bending eccentrically. Quadratus lumborum lies laterally in the lumbar region.

  5. Posterior arm and forearm

    Triceps (radial nerve, C7) extends the elbow. In the forearm, the radial nerve and its posterior interosseous branch supply all the extensors: brachioradialis, the radial wrist extensors, extensor digitorum and ECU superficially; supinator and the outcropping thumb muscles (APL, EPB, EPL) deep.

  6. Gluteal region

    Gluteus maximus (inferior gluteal nerve) extends the hip from flexion. Gluteus medius (superior gluteal nerve) keeps the pelvis level, and its weakness causes the Trendelenburg sign. Piriformis is the key landmark: the superior gluteal vessels and nerve pass above it, and the sciatic nerve emerges below it over the short lateral rotators. Inject only into the superolateral quadrant.

  7. Hamstrings

    Biceps femoris (lateral), semitendinosus and semimembranosus (medial) arise from the ischial tuberosity, extend the hip and flex the knee. All are supplied by the tibial division of the sciatic nerve, except the short head of biceps (common fibular division). Adductor magnus lies deep to them.

  8. Calf: triceps surae

    Gastrocnemius (two heads, crossing the knee) and soleus (deep, mostly slow fibres, the venous "peripheral heart") insert through the calcaneal tendon. All are supplied by the tibial nerve (ankle jerk S1). Popliteus unlocks the knee, and the thin plantaris tendon runs between gastrocnemius and soleus.

Labelled parts