Slicing the Body
Each cardinal plane cuts the body along a different axis, and the section a plane produces determines which structures the cut brings into view. · 11 min
To study what is inside a body without taking it apart, anatomists imagine slicing straight through it with a flat cut. The cut is called a plane, and the flat surface it exposes is a section. Here is the point that matters: the plane you choose decides what the section shows. A cut down the middle and a cut across the waist reveal completely different insides of the same person. There are three standard planes, one for each of the axes you fixed last folio, and this lesson is about naming them and reading what each one lays open.
Guess before you learn
Picture one flat, vertical cut passing straight through the tip of the nose and the navel, dividing the body into equal right and left halves. Before we name it — which pair of directions does that cut separate?
A cut always separates the two sides it lies between: this one has a left half on one side and a right half on the other, so it separates left from right. That plane is the midsagittal plane. Naming a plane is really just naming the directions its section divides — which is why fixing those directions came first.
Undergrad
3–5
The three cuts have names. The sagittal cut is vertical and splits left from right. The frontal cut is also vertical, but it splits front from back. The transverse cut is flat and level, and it splits top from bottom. Two of the cuts stand up tall; one lies down flat. Pick a different cut and you open a different view of the body.
6–8
There are three cardinal planes, each running along two of the body's axes and cutting across the third. The sagittal plane is vertical and divides the body into left and right; a sagittal cut exactly down the middle is the midsagittal (median) plane, and one off to the side is parasagittal. The frontal (coronal) plane is also vertical but divides front (anterior) from back (posterior). The transverse (horizontal) plane lies flat and divides superior from inferior. Any slanted cut that is none of these is an oblique plane. The section is the flat face the cut exposes.
9–12
A plane is fixed by the pair of axes it contains and the one axis it is perpendicular to: the sagittal plane runs superoinferior and anteroposterior, so it cuts the mediolateral axis, splitting left from right. Because a section is only the two-dimensional surface where the plane meets the solid body, one structure yields different sections in different planes. A windpipe — a vertical tube — shows a small ring in a transverse section but a long stripe in a frontal one. Same object, two profiles. Reading anatomy from flat images means always knowing which plane produced them.
K–2
You have three ways to imagine cutting straight through a body. One cut makes a left side and a right side. One makes a front and a back. One makes a top and a bottom.
Each cut shows you something different inside. The cut you pick decides what you get to see.
Undergrad
The three cardinal planes are simply the mutually orthogonal planes of the body-fixed frame established last folio, and a section is the intersection of one such plane with the solid body — a level set of one coordinate. The practical consequence is that sectional anatomy is an inverse problem: a single three-dimensional structure projects to different two-dimensional profiles depending on the cutting plane, and the reader must reconstruct the solid from a stack of slices. Modern imaging leans on this almost entirely; computed tomography, for instance, delivers the body as a dense stack of transverse sections that the eye reassembles into depth.
Postgrad
A cardinal plane selects two of the three body axes; the section it yields is a level set whose shape is governed by the object's geometry relative to the cut. A cylinder sectioned transversely gives a circle, but obliquely gives an ellipse, and lengthwise a rectangle — which is precisely why oblique sections mislead and why standardised planes are worth enforcing. The nomenclature carries redundancy for good historical reasons: coronal equals frontal, axial equals transverse. And the anteroposterior caveat from the previous folio persists here — 'frontal' is meaningful only once the bipedal reference stance has pinned front and back, so the planes inherit the convention rather than escaping it.
section
The flat, two-dimensional surface a plane exposes when it cuts through the body. A transverse section, for example, is what a horizontal cut lays open.
Because the section is only a flat face, the shape a structure shows depends entirely on how the plane meets it. That is why the same organ can look unrecognisable in two different scans. Imaging keeps the old names alongside the anatomical ones: a coronal image is a frontal section, and an axial image is a transverse one, shown as though you were looking up through the body from the feet. Learn to ask of any flat picture of the body: which plane made this? The answer tells you what you are looking at, and what has been cut away.
What shape does the windpipe show in each plane? — the steps fade as you master them
a small ring (a circle)
a long, narrow stripe
same structure, two planes, two shapes — the plane decides the picture
Why is this true?
Why can one organ look completely different in two scans of the same patient?
Because each scan is a section — a flat face cut by a particular plane. A structure meets a transverse plane and a frontal plane along different surfaces, so its outline in one image need not resemble its outline in the other, even though it is the same organ.
Three planes, three axes, three sections: sagittal for left and right, frontal for front and back, transverse for top and bottom — and every flat image of a body is one of them. Keep asking which plane made a picture, because the answer decides what you see and what has been sliced away. Next folio, we stop cutting and look at where the organs actually live: the sealed cavities of the body, and the slippery membranes that line them.
Note
Anatomy rewards drawing over rereading. Sketch each plane over a stick figure from memory, then lay your lines against the plate above and correct only what drifted.
Practice — new ink and old, interleaved
1.Without looking back: name the three cardinal planes and, for each, the two directions its section divides.
Sagittal — left from right; frontal (coronal) — front from back; transverse (horizontal / axial) — top from bottom.
How close were you? Grade yourself honestly — it sets your review date.
2.Match each directional term to its opposite.
3.A single vertical cut separates the chest and belly (front) from the spine and buttocks (back). Which plane is it?
4.A transverse plane descends from the head. Order these structures in the sequence it meets them, top to bottom.
- forehead
- chest
- hip
5.Which of these is the anatomical position?
6.A frontal plane splits the body into an anterior part and a posterior part. Which part contains the spine?
7.This is a right arm drawn from shoulder to hand. Click the part that is distal — farthest from where the limb joins the trunk.
Tap the plate to place your pin.