anatomical planes in humans.

General usage

Three basic reference planes are used in zoological anatomy.

* A sagittal plane, being a plane parallel to the sagittal suture, divides the body into sinister and dexter (left and right) portions.
o The midsagittal or median plane is in the mid line; i.e. it would pass through mid line structures such as the navel or spine, and all other sagittal planes (also referred to as parasagittal planes) are parallel to it. Median can also refer to the midsagittal plane of other structures, such as a digit.
* A coronal or frontal plane divides the body into dorsal and ventral (back and front, or posterior and anterior) portions.
* A transverse plane, also known as an axial plane or cross-section, divides the body into cranial and caudal (head and tail) portions.

For post-embryonic humans a coronal plane is vertical and a transverse plane is horizontal, but for embryos and quadrupeds a coronal plane is horizontal and a transverse plane is vertical.

When describing anatomical motion, these planes describe the axis along which an action is performed. So by moving through the transverse plane, movement travels from head to toe. For example, if a person jumped directly up and then down, their body would be moving through the transverse plane in the coronal and sagittal planes.

Some of these terms come from Latin. Sagittal means "like an arrow", a reference to the position of the spine which naturally divides the body into right and left equal halves, the exact meaning of the term "midsagittal", or to the shape of the sagittal suture, which defines the sagittal plane and is shaped like an arrow.

A longitudinal plane is any plane perpendicular to the transverse plane. The coronal plane and the sagittal plane are examples of longitudinal planes.

[edit] Usage in human anatomy

Sometimes the orientation of certain planes needs to be distinguished, for instance in medical imaging techniques such as sonography, CT scans, MRI scans, or PET scans. One imagines a human in the anatomical position, and an X-Y-Z coordinate system with the X-axis going from front to back, the Y-axis going from left to right, and the Z-axis going from up to down. The X-axis axis is always forward (Tait-Bryan angles) and the right-hand rule applies.

* A transverse (also known as axial or horizontal) plane is an X-Y plane, parallel to the ground, which (in humans) separates the superior from the inferior, or put another way, the head from the feet.
* A coronal (also known as frontal) plane is an X-Z plane, perpendicular to the ground, which (in humans) separates the anterior from the posterior, the front from the back, the ventral from the dorsal.
* A sagittal (also known as median) plane is an Y-Z plane, perpendicular to the ground, which separates left from right. The midsagittal plane is the specific sagittal plane that is exactly in the middle of the body.

The axes and the sagittal plane are the same for bipeds and quadrupeds, but the orientation of the coronal and transverse planes switch. The axes on particular pieces of equipment may or may not correspond to axes of the body, especially since the body and the equipment may be in different relative orientations.

Occasionally, in medicine, abdominal organs may be described with reference to the trans-pyloric plane which is a transverse plane passing through the pylorus.

[edit] Anatomical planes in animal brains

In discussing the neuroanatomy of animals, particularly rodents used in neuroscience research, the convention has been to name the sections of the brain according to the homologous human sections. Hence, what is technically a transverse section with respect to the body of a rat (dividing anterior from posterior) may often be referred to in rat neuroanatomical coordinates as a coronal section, and likewise a coronal section with respect to the body (i.e. dividing ventral from dorsal) in a rat brain is referred to as transverse. This preserves the comparison with the human brain which is rotated with respect to the body axis by 90 degrees in the ventral direction. It does mean that the planes of the rat brain are not necessarily the same as those of the body.

[edit] Surface and other landmarks in humans

In humans, reference may be made to landmarks which are on the skin or visible underneath. As with planes, lines and points are imaginary. Examples include:

* The mid-axillary line, a line running vertically down the surface of the body passing through the apex of the axilla (armpit). Parallel are the anterior axillary line, which passes through the anterior axillary skinfold, and the posterior axillary line, which passes through the posterior axillary skinfold.
* The mid-clavicular line, a line running vertically down the surface of the body passing through the midpoint of the clavicle.
* The mid-pupillary line, a line running vertically down the face through the midpoint of the pupil when looking directly forwards.
* The mid-inguinal point, a point midway between the anterior superior iliac spine and the pubic symphysis.
o mid-point of inguinal ligament = mid-point between anterior superior iliac spine and pubic tubercle
* Tuffier's line, which is a transverse line passing across the lumbar spine between the posterior iliac crests.
* Mid-ventral line, the intersection between the ventral skin and the median plane.

Additionally, reference may be made to structures at specific levels of the spine (e.g. the 4th cervical vertebra, abbreviated "C4"), or the rib cage (e.g. the 5th intercostal space).