Gross anatomy: limbs, thorax, abdomen and pelvis

In short

Gross anatomy of the limbs, thorax, abdomen and pelvis is the regional study of bones, muscles, vessels, nerves, viscera and fascial spaces as they are actually exposed in cadaveric dissection and seen on radiographs, CT and ultrasound. It is the structural grammar of every clinical subject that follows: a fracture, a hernia, a myocardial infarction or an obstructed labour is first an anatomical problem. In the NMC competency-based (CBME) curriculum it is taught in Phase 1 with AN-coded competencies, examined in the First Professional university examination (theory papers, dissection-hall viva, spotting and surface marking), and tested again in NEET-PG, INI-CET, FMGE and PG entrance interviews. Clinically, applied gross anatomy is used daily in surgery, orthopaedics, radiology, anaesthesia (blocks), obstetrics and emergency medicine.

Explained

Framework: terms, planes, joints and the fascial plan

• Anatomical position: erect, eyes forward, palms facing front. All terms (medial/lateral, proximal/distal, flexion/extension) are defined from it; forearm rotation is supination/pronation, thumb movement includes opposition.
• Planes: median/sagittal, coronal, transverse. Clinically used vertebral planes — transpyloric (L1), transtubercular (L5), subcostal (L3), interspinous.
• Joint classes: fibrous (suture, syndesmosis — inferior tibiofibular), cartilaginous (primary = epiphyseal plate; secondary = pubic symphysis, intervertebral), synovial (plane, hinge, pivot, condylar, saddle, ball-and-socket).
• Synovial joint features: articular cartilage, capsule, synovial membrane, variable discs/menisci, bursae. Mobility is bought at the cost of stability — the shoulder dislocates easily, the hip rarely.
• Fascial plan: superficial fascia (fat + fat-containing layers; in the lower abdomen Camper's fatty and Scarpa's membranous layers) and deep fascia dividing limbs into compartments, each with its own nerve — the basis of compartment syndrome and of nerve-block anatomy.
• Dermatome vs cutaneous nerve territory: a dermatome is one spinal segment's skin strip (overlapping, so a single root section is rarely anaesthetic); a cutaneous nerve territory is discrete (a complete nerve section gives a clear patch).

Upper limb

• Bones/ossification: clavicle (first to ossify, membranous, fractures at junction of middle and lateral thirds), scapula, humerus, radius, ulna, 8 carpals, 5 metacarpals, 14 phalanges.
• Brachial plexus: roots C5–T1 → trunks (upper, middle, lower) in posterior triangle → divisions behind clavicle → cords (lateral, medial, posterior) around axillary artery → branches. Mnemonic order of cord branches: lateral pectoral; medial pectoral, medial cutaneous nerves of arm and forearm; posterior cord gives upper and lower subscapular, thoracodorsal, axillary, radial.
• Pre-plexus branches: dorsal scapular nerve (C5) to rhomboids, long thoracic (C5,6,7) to serratus anterior — injury causes winged scapula; suprascapular nerve from upper trunk.
• Axilla: pyramidal space; apex bounded by clavicle, upper border of scapula, outer border of first rib. Contents — axillary artery and vein, brachial plexus cords, axillary lymph nodes (anterior/pectoral, posterior/subscapular, lateral/humeral, central, apical — the route of breast carcinoma spread), long thoracic and thoracodorsal nerves, axillary fat.
• Axillary artery in 3 parts by pectoralis minor: 1 branch (superior thoracic), 2 (thoracoacromial, lateral thoracic), 3 (subscapular, anterior and posterior circumflex humeral). Scapular anastomosis keeps the limb alive if it is ligated.
• Rotator cuff: supraspinatus (abduction initiation), infraspinatus and teres minor (lateral rotation), subscapularis (medial rotation). Supraspinatus tendon is the usual site of degeneration/tear and of the painful arc in impingement.
• Arm compartments: anterior (biceps, coracobrachialis, brachialis — musculocutaneous nerve) and posterior (triceps — radial nerve in the spiral groove).
• Cubital fossa: boundaries — brachioradialis laterally, pronator teres medially, intercondylar line above. Contents medial to lateral: median nerve, brachial artery, biceps tendon (MBBT); radial nerve lies under brachioradialis. Site for venepuncture (median cubital vein) and brachial BP.
• Forearm/hand: flexor compartment (median nerve, with ulnar nerve supplying flexor carpi ulnaris and medial half of flexor digitorum profundus); extensor compartment (radial/posterior interosseous). Carpal tunnel — flexor retinaculum roof; contents 4 FDS + 4 FDP + flexor pollicis longus + median nerve (the ulnar nerve and palmaris longus are outside).
• Hand: thenar and adductor pollicis (median except adductor = ulnar), hypothenar, lumbricals (1st and 2nd median, 3rd and 4th ulnar), palmar and dorsal interossei (ulnar). Superficial palmar arch mainly ulnar, deep arch mainly radial — Allen's test before radial artery cannulation.
• Classic nerve lesions: axillary (surgical neck fracture) — loss of abduction, deltoid patch anaesthesia; radial (mid-shaft humerus) — wrist drop, no triceps loss if below the groove; median (supracondylar/wrist) — pointing index, ape thumb, loss of opposition; ulnar (medial epicondyle, Guyon's canal) — claw hand (worse in distal lesions: ulnar paradox), card and Froment's sign.
• Erb's palsy (C5,6 — upper trunk, excessive shoulder traction): adducted, medially rotated, pronated "policeman's tip" limb. Klumpke's palsy (C8,T1): claw hand with Horner syndrome.

Lower limb

• Gluteal region: gluteus maximus (extensor, inferior gluteal nerve), gluteus medius and minimus (abductors/medial rotators, superior gluteal nerve — injury gives Trendelenburg gait), deep lateral rotators (piriformis, obturator internus, gemelli, quadratus femoris). Structures leave the pelvis above and below piriformis via the greater sciatic foramen. Intramuscular injections go in the upper outer quadrant (or ventrogluteal site) to avoid the sciatic nerve.
• Femoral triangle: inguinal ligament above, medial border of sartorius laterally, medial border of adductor longus medially; floor iliacus, pectineus, adductor longus; contents lateral→medial NAVEL — femoral nerve, artery, vein, empty space, lymphatics (femoral canal, site of femoral hernia, which lies below and lateral to the pubic tubercle).
• Adductor (subsartorial/Hunter's) canal: femoral artery and vein, nerve to vastus medialis, saphenous nerve; artery becomes popliteal at the adductor hiatus.
• Thigh compartments: anterior (quadriceps + sartorius, femoral nerve), medial (adductors, obturator nerve; adductor magnus hamstring part by sciatic), posterior (hamstrings, sciatic).
• Popliteal fossa: diamond — biceps femoris and semimembranosus/semitendinosus above, two heads of gastrocnemius below. Contents superficial→deep: tibial nerve, popliteal vein, popliteal artery (deepest, closest to bone — hence injury in supracondylar femur fracture and knee dislocation), common peroneal nerve at the lateral margin.
• Knee: cruciates (ACL prevents anterior tibial glide — anterior drawer/Lachman; PCL prevents posterior glide), collaterals, menisci (medial is C-shaped, more often torn; unhappy triad = ACL + MCL + medial meniscus). Locking is medial rotation of femur; popliteus unlocks.
• Leg compartments: anterior (dorsiflexors, deep peroneal), lateral (peronei, superficial peroneal), posterior (gastrocnemius-soleus, deep flexors, tibial nerve). Common peroneal nerve at the neck of fibula is the most commonly injured nerve of the lower limb — foot drop with high-stepping gait and loss of eversion.
• Foot: medial and lateral longitudinal and transverse arches; supported by bone shape, plantar ligaments (spring ligament, long and short plantar, plantar aponeurosis) and tendons (tibialis posterior, peroneus longus, intrinsic muscles). Loss gives pes planus. Tarsal tunnel transmits tibial nerve behind the medial malleolus (Tom, Dick and a Very Nervous Harry).
• Veins and lymphatics: great saphenous vein (in front of medial malleolus → femoral vein; used for cut-down and grafts) and small saphenous (behind lateral malleolus → popliteal); perforators with valves — incompetence causes varicose veins and medial-side venous ulcers.

Thorax

• Thoracic cage: 12 vertebrae, 12 pairs of ribs (1–7 true, 8–10 false, 11–12 floating), sternum. Sternal angle = T4/T5 disc — level of the second costal cartilage, arch of aorta begins and ends, bifurcation of trachea, upper limit of the pulmonary trunk, and the plane dividing superior from inferior mediastinum.
• Intercostal space: external, internal and innermost intercostals; the vein, artery, nerve (VAN) lie in the subcostal groove from above downward — so an intercostal drain or needle is passed just above the lower rib, in the "safe triangle" (lateral to pectoralis major, anterior to latissimus dorsi, above the fifth intercostal space).
• Mediastinum: superior; inferior = anterior (thymus remnant), middle (pericardium, heart, roots of great vessels, phrenic nerves), posterior (descending aorta, oesophagus, thoracic duct, azygos system, sympathetic chain, splanchnic nerves).
• Pleura and lungs: parietal pleura (costal, mediastinal, diaphragmatic, cervical) is pain-sensitive (intercostal and phrenic); visceral is not. Lung root structures: bronchus posterior, pulmonary artery, veins anterior/inferior. Right lung 3 lobes/10 segments, left 2 lobes/8–10 segments — bronchopulmonary segments are the units of resection and of postural drainage. The right main bronchus is wider, shorter and more vertical, so aspirated bodies usually go right.
• Heart: pericardium (fibrous + serous; sinuses — oblique and transverse). Surfaces — sternocostal mostly right ventricle, base mostly left atrium, diaphragmatic left + right ventricle. Apex beat in the left 5th intercostal space, ~9 cm from the midline.
• Coronary arteries: right coronary (right marginal, posterior interventricular in ~70% = right dominance) supplies right atrium and ventricle, SA node in ~60% and AV node in ~80%, and the inferior wall and posterior interventricular septum; left coronary → left anterior descending (anterior two-thirds of septum, anterior LV, apex — the "widow-maker") and circumflex (left atrium, lateral LV).
• Conducting system and valve areas: SA node at the superior cavoatrial junction; AV node in the triangle of Koch. Auscultation — aortic right 2nd space, pulmonary left 2nd space, tricuspid lower left sternal edge, mitral apex.
• Diaphragm openings: T8 IVC and right phrenic branches (caval opening), T10 oesophagus with vagi (oesophageal), T12 aorta, thoracic duct, azygos (aortic). Motor supply is only the phrenic nerve (C3,4,5 "keeps the diaphragm alive"); irritation refers pain to the shoulder tip.
• Thoracic duct drains all the body except the right upper quadrant; ascends right of the midline, crosses to the left at T5 and opens into the left brachiocephalic vein.

Abdomen: wall, peritoneum and viscera

• Nine regions by two vertical mid-clavicular and two horizontal (subcostal and transtubercular) lines. Flat muscles — external oblique, internal oblique, transversus abdominis — form the rectus sheath: above the arcuate line (midway umbilicus–pubis) the posterior wall is present; below it, all aponeuroses pass in front, so the posterior wall is deficient. Nerve supply T7–T11, subcostal (T12), iliohypogastric and ilioinguinal (L1); T10 at the umbilicus.
• Inguinal canal: ~4 cm, from deep ring (in transversalis fascia, above the midpoint of the inguinal ligament) to superficial ring (in external oblique aponeurosis, above and medial to the pubic tubercle). Anterior wall external oblique (+ internal oblique laterally), posterior wall transversalis fascia (+ conjoint tendon medially), roof arching internal oblique/transversus, floor inguinal ligament with lacunar ligament. Contents: spermatic cord (or round ligament), ilioinguinal nerve. Hesselbach's triangle = inguinal ligament, rectus margin, inferior epigastric artery — a direct hernia comes through it.
• Peritoneum: greater sac and lesser sac (omental bursa) communicating through the epiploic foramen of Winslow (anterior — free margin of lesser omentum with portal triad; posterior — IVC; superior — caudate lobe; inferior — first part of duodenum). Mesenteries, omenta, ligaments, paracolic gutters and the hepatorenal pouch of Morison (lowest part supine — site of subphrenic abscess and of FAST ultrasound fluid).
• Foregut, midgut, hindgut: coeliac trunk (to mid-duodenum; branches left gastric, splenic, common hepatic), superior mesenteric (to the junction of proximal two-thirds and distal third of transverse colon), inferior mesenteric (to the upper rectum). Referred pain accordingly epigastric, umbilical, hypogastric — why appendicitis starts periumbilical (T10) and shifts to the right iliac fossa when parietal peritoneum is involved.
• Stomach and duodenum: stomach beds, lesser and greater omenta, arterial circle of two arches. Duodenum C-shaped, 4 parts, retroperitoneal except the first; the superior mesenteric artery and vein cross the third part (basis of SMA syndrome). The bile and pancreatic ducts enter at the ampulla of Vater (major papilla, second part) with the sphincter of Oddi.
• Liver: anatomical lobes by falciform ligament; functional (Couinaud) segments I–VIII by the planes of the hepatic veins and portal divisions — the basis of segmental resection. Porta hepatis contents: right and left hepatic ducts (anterior), hepatic artery, portal vein (posterior). Calot's triangle (cystic duct, common hepatic duct, inferior liver surface) contains the cystic artery — key in cholecystectomy. Gall bladder fundus at the tip of the 9th costal cartilage (Murphy's sign).
• Pancreas, spleen: pancreas retroperitoneal across L1–L2; spleen in the left hypochondrium along the 9th–11th ribs, 1″×3″×5″, 7 oz, related to the left colic flexure, stomach, kidney, tail of pancreas; ligaments gastrosplenic and splenorenal (containing splenic vessels).
• Kidneys and suprarenals: retroperitoneal, T12–L3, right slightly lower; coverings — fibrous capsule, perirenal fat, renal fascia, pararenal fat. Hilum front to back vein, artery, pelvis (VAP). Ureter crosses the pelvic brim at the bifurcation of the common iliac and is constricted at the pelviureteric junction, the brim and the bladder wall — where stones lodge; pain refers loin to groin (T11–L2).
• Portocaval anastomoses (sites of varices in portal hypertension): lower oesophagus, umbilicus (caput medusae), anal canal, retroperitoneal (Retzius) and patent ductus venosus/paraumbilical.

Pelvis and perineum

• Bony pelvis: false (above the brim) and true pelvis. Obstetric diameters of the inlet — transverse ~13 cm (largest), oblique ~12 cm, anteroposterior/true conjugate ~11 cm (diagonal conjugate measured clinically ~12.5 cm); the outlet's largest diameter is anteroposterior. Types: gynaecoid, android, anthropoid, platypelloid.
• Pelvic walls and floor: obturator internus and piriformis walls; pelvic diaphragm = levator ani (pubococcygeus, puborectalis, iliococcygeus) + coccygeus, supplied by S3,4 and the nerve to levator ani/pudendal branches. Perineal body is the central tendon — protected by episiotomy; its tear causes prolapse and incontinence.
• Perineum: urogenital and anal triangles. Superficial perineal pouch (between Colles' fascia and perineal membrane) — crura of penis/clitoris, bulb, ischiocavernosus, bulbospongiosus, superficial transverse perinei, branches of perineal vessels and nerves; rupture of the bulbar urethra extravasates urine here. Deep perineal pouch — sphincter urethrae, deep transverse perinei, membranous urethra, bulbourethral glands (male), part of the vagina (female).
• Ischio-anal fossa: fat-filled wedge lateral to the anal canal, crossed by inferior rectal vessels and nerves; communicates across the midline behind the anal canal — hence horseshoe abscess and fistula-in-ano.
• Anal canal: above the pectinate line — endoderm origin, columnar, superior rectal artery, portal drainage, autonomic (painless internal haemorrhoids), nodes to internal iliac; below — ectoderm, squamous, inferior rectal artery, systemic drainage, somatic pudendal (painful), nodes to superficial inguinal.
• Uterus and supports: anteverted, anteflexed; broad, round, uterosacral, transverse cervical (Mackenrodt's) ligaments; levator ani is the real support. Blood supply uterine artery (from internal iliac), which crosses above and in front of the ureter about 2 cm lateral to the cervix — "water under the bridge", the ureter at risk in hysterectomy.
• Prostate: base, apex, lobes; zones — peripheral (carcinoma, palpable per rectum) and transition/central (benign hyperplasia causing obstruction). Prostatic venous plexus communicates with internal vertebral veins — route of bony metastasis.
• Internal iliac artery: anterior division (superior and inferior vesical, middle rectal, uterine, vaginal, obturator, internal pudendal, inferior gluteal) and posterior division (iliolumbar, lateral sacral, superior gluteal). Sacral plexus L4–S4 gives sciatic, pudendal (S2,3,4), superior and inferior gluteal nerves.
• Pudendal nerve leaves through the greater sciatic foramen, hooks round the ischial spine, re-enters via the lesser sciatic foramen into the pudendal (Alcock's) canal — blocked at the ischial spine for operative delivery.

Indian practice, regulation and how it is taught

• Curriculum: NMC CBME (2019, revised 2024 guidelines) — Anatomy competencies coded AN, taught with dissection, prosection, histology, radiological and surface anatomy, early clinical exposure and integration sessions; internal assessment plus a First Professional university examination with theory, practical/spotting, surface marking and viva.
• Cadavers: obtained by voluntary body donation and unclaimed bodies under the state Anatomy Acts (each state has its own, e.g. the Bombay/Maharashtra, Delhi, Kerala Anatomy Acts) — commercial dealing in bodies is not permitted and dignity-of-the-dead norms apply. Organ and tissue retrieval for transplant is governed separately by the Transplantation of Human Organs and Tissues Act, 1994 (amended 2011) and NOTTO rules.
• Safety: formalin/formaldehyde exposure in the dissection hall is controlled by ventilation and PPE; occupational-safety duties now sit under the Occupational Safety, Health and Working Conditions Code, 2020, in force from 21 November 2025 (it subsumed the Factories Act); biomedical waste follows the Bio-Medical Waste Management Rules, 2016 as amended.
• Imaging-based anatomy (X-ray, CT, MRI, ultrasound, cadaver-CT correlation) is now examined; radiation use is licensed under AERB rules.

Key points

• Sternal angle (T4/5) - rib 2, aortic arch limits, tracheal bifurcation, superior/inferior mediastinal plane.
• Diaphragm openings - T8 IVC, T10 oesophagus + vagi, T12 aorta + thoracic duct + azygos.
• Phrenic nerve (C3,4,5) - sole motor supply of the diaphragm; refers pain to the shoulder tip.
• Intercostal VAN - vein, artery, nerve from above down; insert chest drains above the lower rib.
• Axillary nodes - breast lymph drainage; levels I–III guide axillary dissection.
• Long thoracic nerve - serratus anterior; injury = winged scapula.
• Radial nerve in the spiral groove - wrist drop with triceps spared.
• Ulnar paradox - a distal ulnar lesion gives a worse claw than a proximal one.
• Carpal tunnel - 9 tendons + median nerve; ulnar nerve is outside it.
• Femoral triangle NAVEL - nerve, artery, vein, empty space, lymphatics from lateral to medial.
• Popliteal artery - deepest in the fossa; injured in supracondylar fracture and knee dislocation.
• Common peroneal nerve at the fibular neck - foot drop, loss of eversion and dorsiflexion.
• Superior gluteal nerve - abductors; injury gives Trendelenburg sign.
• Arcuate line - rectus sheath has no posterior wall below it.
• Hesselbach's triangle - direct hernia is medial to the inferior epigastric artery; indirect is lateral.
• Foramen of Winslow - only communication of the lesser sac; portal triad in front, IVC behind.
• Calot's triangle - cystic artery; the hazard zone of laparoscopic cholecystectomy.
• Ureter and uterine artery - water (ureter) under the bridge (artery); ureteric injury in hysterectomy.
• Pectinate line - divides the anal canal in origin, epithelium, blood supply, nerve supply and lymph drainage.
• Pudendal block at the ischial spine - anaesthetises the perineum for instrumental delivery.

Examples

Case 1 — Fall on the shoulder, arm cannot be lifted. A 24-year-old cannot abduct the right arm after a fall; X-ray shows a fracture of the surgical neck of the humerus; sensation is lost over the lower deltoid.

1. The axillary nerve and posterior circumflex humeral artery wind round the surgical neck.
2. Deltoid paralysis → abduction beyond the first 15° lost (supraspinatus can still initiate).
3. The "regimental badge" patch is the upper lateral cutaneous nerve of the arm (axillary branch).
4. Diagnosis: axillary nerve palsy. Shaft (not neck) fractures would instead threaten the radial nerve → wrist drop.

Case 2 — Groin swelling. A 55-year-old man has a reducible swelling appearing on coughing, above and medial to the pubic tubercle, that reappears immediately on coughing after reduction with the deep ring occluded.

1. Above and medial to the pubic tubercle = inguinal, not femoral (femoral lies below and lateral).
2. Occluding the deep ring would control an indirect hernia; it did not.
3. Direct inguinal hernia, bulging through Hesselbach's triangle medial to the inferior epigastric artery, due to a weak transversalis fascia/conjoint tendon.

Case 3 — Inferior-wall myocardial infarction. ECG shows ST elevation in II, III and aVF with bradycardia.

1. Leads II, III, aVF view the inferior (diaphragmatic) surface — mostly the right and left ventricle supplied by the posterior interventricular artery.
2. In ~70% of people that artery arises from the right coronary artery (right dominance).
3. The RCA also supplies the AV node in ~80% — hence the bradycardia/heart block.
4. Culprit vessel: right coronary artery. Anterior septal infarction (V1–V4) would implicate the LAD.

Case 4 — Haematemesis with a distended abdomen. A patient with cirrhosis vomits blood; there are dilated veins radiating from the umbilicus and a palpable spleen.

1. Portal hypertension forces blood into portosystemic channels.
2. Lower oesophagus: left gastric (portal) ↔ oesophageal veins of azygos (systemic) → varices and bleeding.
3. Umbilicus: paraumbilical ↔ superficial abdominal veins → caput medusae.
4. Also anorectal (superior ↔ middle/inferior rectal) and retroperitoneal channels; splenomegaly is from back-pressure in the splenic vein.

Case 5 — Foot drop after a plaster cast. After a below-knee cast, a patient cannot dorsiflex or evert the foot and has numbness over the dorsum, but inversion and plantar flexion are normal.

1. Dorsiflexors = anterior compartment (deep peroneal); evertors = lateral compartment (superficial peroneal).
2. Both branches arise from the common peroneal nerve at the neck of the fibula, where the cast compressed it.
3. Inversion (tibialis posterior, tibial nerve) and plantar flexion are spared → the lesion is not sciatic or tibial.
4. Sensory loss: dorsum of foot (superficial peroneal) and first web space (deep peroneal).

Where it is used

• Surgery and orthopaedics: incisions along Langer's lines and nerve-sparing planes, hernia repair, laparoscopic cholecystectomy via Calot's triangle, fracture fixation and compartment release — AIIMS, PGIMER, CMC Vellore, Apollo, Fortis and district hospital theatres alike.
• Anaesthesia and critical care: brachial plexus (interscalene, supraclavicular, axillary) blocks, transversus abdominis plane block, pudendal and caudal blocks, subclavian and internal jugular central lines, intercostal drains.
• Radiology and ultrasound: CT/MRI sectional anatomy, FAST scanning of Morison's pouch, segmental liver reporting for resection planning, interventional radiology access routes.
• Obstetrics and gynaecology: pelvimetry and the mechanism of labour, episiotomy, pudendal block, avoiding the ureter in hysterectomy — core to the national maternal-health programmes.
• Teaching and research posts: Anatomy Assistant Professor/Tutor jobs in government and private medical colleges under NMC norms; plastination and museum work, body-donation programme coordination.
• Allied roles: physiotherapy and sports medicine (muscle actions, joint stability), forensic medicine (injury interpretation), medical illustration, surgical device and implant companies, and medical-education content firms.

Interview questions

• Q: Why is a chest drain inserted just above the lower rib of an intercostal space? A: The intercostal vein, artery and nerve run in the subcostal groove at the upper part of the space, so passing close to the lower rib's upper border avoids them.
• Q: What structures lie at the level of the sternal angle? A: The T4/T5 disc, second costal cartilage, beginning and end of the aortic arch, bifurcation of the trachea and the plane between superior and inferior mediastinum.
• Q: A patient has winged scapula. Which nerve and muscle are involved? A: The long thoracic nerve (C5,6,7) supplying serratus anterior, which normally holds the scapula against the chest wall.
• Q: Differentiate a direct from an indirect inguinal hernia anatomically. A: An indirect hernia enters the deep ring lateral to the inferior epigastric artery and runs within the cord coverings; a direct hernia bulges through Hesselbach's triangle medial to that artery.
• Q: Why does appendicitis pain begin near the umbilicus and later shift to the right iliac fossa? A: Visceral pain from the midgut appendix is referred to the T10 dermatome; once the inflamed parietal peritoneum is involved, somatic nerves localise it to the right iliac fossa.
• Q: Why do aspirated foreign bodies usually enter the right lung? A: The right main bronchus is shorter, wider and more vertical than the left.
• Q: Which artery is at risk in a supracondylar fracture of the femur, and why? A: The popliteal artery — it is the deepest structure in the popliteal fossa, lying directly on the bone and capsule.
• Q: Explain the ulnar paradox. A: A lesion at the wrist spares the long flexors (FDP), so their unopposed pull makes the claw more marked than in a lesion at the elbow, where FDP to the ring and little fingers is also paralysed.
• Q: Why is the ureter vulnerable during hysterectomy? A: The uterine artery crosses above and in front of the ureter about 2 cm lateral to the cervix — "water under the bridge" — so the ureter can be clamped or ligated with the artery.
• Q: Which zone of the prostate gives rise to carcinoma and which to benign hyperplasia? A: Carcinoma mainly arises in the peripheral zone (palpable on digital rectal examination); benign hyperplasia arises in the transition zone, causing obstruction.
• Q: Why is the pectinate line clinically important? A: It separates two different origins, epithelia, blood supplies, venous and lymphatic drainages and innervations — so internal haemorrhoids above it are painless and external ones below it are painful.
• Q: Why is the ischial spine the landmark for a pudendal block? A: The pudendal nerve hooks around the ischial spine as it re-enters the perineum through the lesser sciatic foramen, where it is easily palpated vaginally.

Common mistakes

• Confusing anatomical liver lobes (falciform ligament) with Couinaud's functional segments, which surgeons actually use.
• Placing the hilar structures wrongly — renal hilum is vein, artery, pelvis from front to back, while the lung root has the bronchus most posterior.
• Saying the ulnar nerve or palmaris longus passes through the carpal tunnel.
• Mixing femoral and inguinal hernias: the pubic tubercle relation (below-lateral versus above-medial) is the deciding sign.
• Quoting the diaphragmatic openings as T8, T10, T12 but attaching the wrong contents — the thoracic duct goes with the aorta, not the IVC.
• Giving intramuscular gluteal injections in the upper inner quadrant, risking the sciatic nerve.
• Reciting dermatomes as exact, non-overlapping zones, and then expecting total anaesthesia from a single root lesion.
• Describing the rotator cuff as including deltoid or teres major, and forgetting that supraspinatus starts abduction.

Related topics

Head, neck and neuroanatomy · Histology and embryology · Physiology: blood, nerve, muscle and cardiorespiratory systems · Surface and radiological anatomy · General surgery: hernia and biliary disease · Obstetrics: mechanism of labour and pelvimetry