The principal planes
Three mutually perpendicular planes describe any orientation in the body, and a fourth name, median, marks the one sagittal plane in the midline.
| Plane | Orientation | Divides the body into |
|---|---|---|
| Median (midsagittal) | Vertical, front to back, through the midline | Equal right and left halves |
| Sagittal (parasagittal) | Vertical, parallel to the median plane | Unequal right and left parts |
| Coronal (frontal) | Vertical, side to side, at right angles to the median plane | Anterior and posterior parts |
| Transverse (horizontal, axial) | Horizontal, at right angles to the other two | Superior and inferior parts |
The sagittal plane takes its name from the sagittal suture of the skull, which runs front to back; the coronal plane from the coronal suture, which runs side to side. Any plane that is not parallel to one of these is an oblique plane.
For a limb or an organ, a longitudinal section runs along its long axis and a transverse section, or cross-section, cuts across it. A cross-section of the forearm is transverse to the forearm even when the forearm is held horizontally.
Axes and movement
Every joint movement takes place in a plane and around an axis that is perpendicular to that plane.
| Movement | Plane | Axis |
|---|---|---|
| Flexion and extension | Sagittal | Transverse (side-to-side) |
| Abduction and adduction | Coronal | Anteroposterior |
| Medial and lateral rotation | Transverse | Vertical (longitudinal) |
Two exceptions matter. The thumb lies rotated at about a right angle to the fingers, so its flexion and extension occur in the plane of the palm and its abduction and adduction at right angles to the palm. The scapula lies angled forwards on the chest wall, so abduction of the arm in the plane of the scapula (scaption) is slightly anterior to the coronal plane.
Named planes of the trunk
Several horizontal planes through the trunk are defined by surface landmarks and used to locate deeper structures. Their vertebral levels are approximate and vary between individuals and with posture.
- Sternal angle plane: through the manubriosternal joint and the T4/T5 intervertebral disc. The second costal cartilage attaches at this level; the arch of the aorta begins and ends and the trachea bifurcates close to it.
- Transpyloric plane: midway between the jugular notch and the upper border of the pubic symphysis, at about L1. It passes near the pylorus, the fundus of the gallbladder, the neck of the pancreas and the hila of the kidneys.
- Subcostal plane: through the lowest points of the costal margins (the tenth costal cartilages), at about L3.
- Supracristal plane: through the highest points of the iliac crests, at about L4. It is used to find the L4 spinous process for lumbar puncture.
- Transtubercular plane: through the tubercles of the iliac crests, at about L5.
Vertical midclavicular lines combine with the subcostal and transtubercular planes to divide the abdomen into nine regions.
Planes in imaging and dissection
Cross-sectional imaging is displayed in the same three planes. CT is acquired as axial (transverse) slices and reconstructed into coronal and sagittal images; MRI can be acquired directly in any plane. By convention, axial images are viewed from below, as if standing at the patient's feet, so the patient's right is on the viewer's left and anterior is at the top of the image.
In the dissecting room, prosections are often cut in these planes: a median sagittal section of the head or pelvis, a coronal section of the brain, or transverse sections of the limbs. Identifying the plane first is the fastest way to orient a specimen.