Appearance
4.1 — The Language of Anatomy
A radiologist writes: a 2 cm lesion in the superior segment of the right lower lobe, posterior to the oblique fissure, with no involvement of the mediastinum. Every word in that sentence is a position, and once you can read it, you know exactly where the lesion is without seeing the scan.
This page is the vocabulary. It is short, it is used on every page from here to the end of the volume, and learning it once means you never have to guess again — including when you are reading your own report.
Why anatomy needs its own words
Ordinary words fail because they depend on how the body is arranged at the time. "Above the wrist" means something different when the arm is raised. "Behind the hand" changes when the palm turns over.
So anatomy fixes a reference position and describes everything from it.
The anatomical position: standing upright, feet slightly apart and flat on the floor, arms at the sides, palms facing forward, head and eyes facing forward.
That palms-forward detail is the one people forget, and it matters. In this position the two forearm bones lie parallel — the radius on the thumb side, the ulna on the little-finger side. Turn the palm down and the radius crosses over the ulna, and any description of which is where becomes wrong. Every anatomical statement in this book assumes the anatomical position, regardless of how the body actually is.
The planes
Sagittal — a vertical plane dividing the body into left and right. The one exactly down the middle is the midsagittal or median plane. The name comes from the Latin sagitta, arrow, because the suture running front to back along the top of the skull was thought to resemble an arrow's path.
Coronal (frontal) — a vertical plane dividing front from back. Named from corona, crown, after the line where a crown sits.
Transverse (axial) — a horizontal plane dividing upper from lower. This is the standard plane for CT scans, and it is why a CT is presented as a stack of slices you scroll through from head to foot.
One convention that confuses everyone the first time. On a transverse image, the patient's left appears on the right of the picture. The image is viewed as though you are standing at the foot of the bed looking up at the patient. So a mass "on the left of the image" is on the patient's right. Getting this backwards has caused wrong-side surgery, which is why modern practice requires the surgical site to be physically marked on the skin before anaesthesia.
Directions
| Term | Means | Example |
|---|---|---|
| Superior / cranial | Toward the head | The heart is superior to the stomach |
| Inferior / caudal | Toward the feet | The bladder is inferior to the navel |
| Anterior / ventral | Toward the front | The sternum is anterior to the heart |
| Posterior / dorsal | Toward the back | The kidneys are posterior to the intestines |
| Medial | Toward the midline | The nose is medial to the eyes |
| Lateral | Away from the midline | The ears are lateral to the eyes |
| Proximal | Nearer the trunk | The elbow is proximal to the wrist |
| Distal | Further from the trunk | The fingers are distal to the wrist |
| Superficial | Nearer the surface | Skin is superficial to muscle |
| Deep | Further from the surface | Bone is deep to muscle |
Proximal and distal are limb words only. You cannot say the stomach is distal to anything meaningfully — it is not on a limb.
Ventral and dorsal are inherited from four-legged animals, where the belly faces down and the back faces up. In a human standing upright, ventral means anterior and dorsal means posterior. In neuroanatomy the two systems collide awkwardly, because the brain sits at a bend relative to the spinal cord, and Chapter 11.5 flags that where it matters.
Ipsilateral means the same side; contralateral the opposite side. These matter enormously in neurology, because most motor pathways cross: a stroke on the left side of the brain causes weakness on the right side of the body, and knowing that lets you localise a lesion from the examination alone (Chapter 18.6).
Bilateral means both sides; unilateral one side.
Movements
Needed constantly from Part 6 onward.
Flexion decreases the angle at a joint — bending the elbow. Extension increases it — straightening the elbow. (The knee is confusing until you think about it developmentally: flexion bends the leg backwards, because the lower limb rotates during development.)
Abduction moves a limb away from the midline; adduction brings it back. The memory aid is that abduction takes it away, as in an abduction.
Rotation turns around the long axis. Medial rotation turns the front of the limb toward the midline, lateral rotation away.
Supination turns the palm up; pronation turns it down. Supination is the anatomical position. The memory aid people actually use is that you carry soup in a supinated hand.
Dorsiflexion lifts the foot upward at the ankle; plantarflexion points it down. Inversion turns the sole inward, eversion outward. The classic ankle sprain is an inversion injury, tearing the ligaments on the outer side, and it accounts for the large majority of ankle injuries (Chapter 5.8).
Circumduction is a circular movement combining several of the above, as when you swing your arm in a circle.
The body cavities
The trunk is divided into sealed compartments, and knowing which one a problem is in tells you a great deal about how it will behave and spread.
The thoracic cavity, above the diaphragm, contains three separate sub-compartments:
- Two pleural cavities, one around each lung, each lined by a two-layered membrane called the pleura with a thin film of fluid between the layers.
- The mediastinum, the space between the lungs, containing the heart in its own sac (the pericardium), the great vessels, the oesophagus, the trachea and the thymus.
They are separate, and that separation is clinically decisive. A punctured lung on one side collapses that lung only, because the other pleural cavity is a sealed space of its own. If both were continuous, every chest injury would be immediately fatal. Chapter 8.2.
The abdominal cavity, below the diaphragm, contains the stomach, intestines, liver, gallbladder, spleen and pancreas. The pelvic cavity below it contains bladder, rectum and reproductive organs. The two are continuous, which is why infection or blood spreads freely between them — and why an inflamed appendix can produce pain and collections down in the pelvis.
Peritoneum is the membrane lining the abdominal cavity and covering most of its organs. An organ suspended within it on a fold of peritoneum is intraperitoneal; one lying behind it against the back wall is retroperitoneal. The kidneys, the pancreas, the aorta and most of the duodenum are retroperitoneal, and this matters because a bleed there is contained by tissue rather than filling the abdomen, so it can be silent for longer and presents with back pain rather than abdominal signs.
The regions of the abdomen
Abdominal pain is one of the commonest reasons anyone sees a doctor, and location is the first and most useful clue. Two schemes are used.
The four-quadrant scheme, dividing at the navel with a vertical and a horizontal line:
- Right upper quadrant — liver, gallbladder, right kidney, part of the colon. Gallstone pain lives here.
- Left upper quadrant — stomach, spleen, pancreas tail, left kidney.
- Right lower quadrant — appendix, right ovary and tube, caecum. Appendicitis lives here, and the specific point most tender is called McBurney's point, one third of the way from the front of the hip bone to the navel.
- Left lower quadrant — sigmoid colon, left ovary and tube. Diverticulitis lives here.
The nine-region scheme is more precise and gives the terms that appear in reports: epigastric (upper middle), umbilical (central), hypogastric or suprapubic (lower middle), with right and left hypochondriac, lumbar and iliac regions on the sides.
And pain moves in patterns worth knowing. Appendicitis classically begins as a vague central pain around the navel and then shifts to the right lower quadrant over several hours. The reason is genuinely instructive: the early pain is from the inflamed appendix itself, whose nerve supply is autonomic and poorly localised, referred to the mid-abdomen. Once inflammation spreads to touch the peritoneum lining the abdominal wall — which has ordinary somatic nerves and precise localisation — the pain becomes sharp and exactly located. The migration of the pain is the diagnosis, and it comes from two different nerve supplies (Chapter 11.9).
Some words that will otherwise trip you
Medical vocabulary is largely Greek and Latin components stuck together, and about twenty of them decode most of it.
| Prefix or suffix | Means | Example |
|---|---|---|
| a-, an- | without | anaemia — without blood |
| hyper- | above, excessive | hypertension |
| hypo- | below, deficient | hypoglycaemia |
| -itis | inflammation | appendicitis |
| -osis | condition, often abnormal | fibrosis |
| -ectomy | surgical removal | appendicectomy |
| -otomy | cutting into | craniotomy |
| -ostomy | making an opening | colostomy |
| -aemia | in the blood | septicaemia |
| -uria | in the urine | haematuria |
| -pathy | disease | neuropathy |
| -algia | pain | neuralgia |
| -plegia | paralysis | hemiplegia |
| -megaly | enlargement | hepatomegaly |
| cardi- | heart | cardiomyopathy |
| hepat- | liver | hepatitis |
| nephr-, ren- | kidney | nephritis, renal |
| pulmon-, pneum- | lung | pneumonia |
| gastr- | stomach | gastritis |
| haem-, hem- | blood | haemorrhage |
Two pairs are worth extra care because confusing them is dangerous. Hyper- and hypo- differ by one letter and mean opposite things: hyperkalaemia is too much potassium and hypokalaemia too little, and the treatments are opposite. Handwritten abbreviations of these have caused deaths, which is why they are written in full in modern practice.
And -ectomy versus -ostomy. A colectomy removes bowel; a colostomy brings bowel to the skin surface. Different operations entirely.
What the next page fixes
You can now say where something is. The next question is what it is made of — because every organ in the body, however different it looks, is built from combinations of just four tissue types. Chapter 4.2 covers epithelium, connective tissue, muscle and nervous tissue: what each looks like under a microscope, where each is found, and what disease each gives rise to when it fails.