Surface regions of the body

Axial and appendicular regions

The body is first divided into two great regions. The axial region is the central axis: the head, the neck and the trunk. The trunk contains the thorax (chest), the abdomen and the pelvis. The appendicular region is made of the appendages, the upper limbs and the lower limbs, including the girdles that attach them to the trunk. This split is not just tidiness: the axial region protects the brain, heart, lungs and abdominal organs, while the appendicular region provides movement and manipulation. Many clinical descriptions begin by naming which of the two regions is involved, because the causes and consequences differ. A pain in the axial region may concern a deep organ; a pain in the appendicular region often concerns a joint, muscle or bone.

For example: A fractured wrist is an appendicular problem; chest pain from a heart problem is axial. The region guides the first questions.

Named regions of the trunk and limbs

Anatomical regions have standard names. The head is the cephalic region, the neck the cervical region, the chest the thoracic region. The abdomen is the abdominal region and the lower trunk the pelvic region. The back is divided into the vertebral region along the spine and the dorsal region over the shoulder blades. On the upper limb, the arm between shoulder and elbow is the brachial region, the forearm the antebrachial region, and the wrist the carpal region. On the lower limb, the thigh is the femoral region, the leg between knee and ankle the crural region, and the ankle and foot the tarsal and pedal regions. The armpit is the axillary region and the groin the inguinal region. These names let a clinician say exactly which part is meant without listing muscles or bones.

For example: “Brachial” means the arm between shoulder and elbow, not the whole upper limb. Saying “the brachial region” avoids the everyday confusion between arm and forearm.

Common misconception: In anatomy, “arm” is only the segment from shoulder to elbow; the whole limb is the upper limb, and the forearm is a separate region.

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Surface landmarks you can see and feel

A landmark is a structure you can identify on the surface, and it acts as an anchor for description and for procedures. Common examples include the clavicle (collar bone) across the top of the chest, the sternum (breastbone) in the midline, the ribs and the costal margin where they end, the umbilicus (navel) in the centre of the abdomen, the iliac crest felt at the top of the hip, the anterior superior iliac spine at its front corner, the patella (kneecap), and the spinous processes felt as a ridge down the back. On the posterior knee the hollow is the popliteal region, and at the front of the elbow the cubital fossa is where vessels and nerves lie close to the surface. Landmarks are reliable because they do not change with body weight as much as the soft tissue around them.

For example: The anterior superior iliac spine is a reliable landmark for finding the level of a lumbar puncture or for locating the appendix.

Using landmarks to describe a finding

A useful description names the side, the region and at least one landmark, then adds size, colour or depth as needed. “A rash on the right upper back, over the medial border of the shoulder blade” is far more useful than “a rash on the back”. “A pulse felt at the anterior wrist, lateral to the tendon in the middle” locates the radial pulse precisely. Landmarks also let a clinician measure: the distance from the sternal notch to a wound, or the height of a swelling above the patella, is meaningful because the anchor is fixed. When you describe a symptom, imagine the next person reading your note without seeing the patient; if they could place a finger on the same spot, the description is complete enough.

For example: “Swelling 3 cm above the right patella” is repeatable by another clinician, because the kneecap is a fixed anchor.

Why surface anatomy matters in care

Surface anatomy guides many everyday procedures and observations. Taking a pulse means knowing where an artery lies close to the surface and over a firm base, such as the radial, brachial, carotid, femoral and popliteal pulses. Giving an injection safely means recognising regions with few vital structures at the chosen depth, and avoiding nerves and vessels. Listening to the chest means placing the stethoscope over known lung and heart regions rather than at random. Measuring blood pressure means finding the brachial artery and wrapping the cuff at the right level. In each case the skill depends on being able to find a landmark quickly by touch and to translate what you feel into a precise description.

For example: The brachial pulse is felt on the medial side of the upper arm, between the biceps and the humerus, which is why the blood-pressure cuff is placed there.