2.3 Body Planes and Cavities

A plane is an imaginary two-dimensional surface that passes through the body. A section is a two-dimensional surface that has been “cut” from a three-dimensional structure.

There are four planes commonly referred to in animal anatomy and medicine:

1. The median plane is the plane that divides the body or an organ vertically into right and left sides equally. It is also called the midsagittal plane or the midline.
2. The sagittal plane is the plane that divides the body or an organ unequally into right and left sides. If this vertical plane runs directly down the middle of the body or an organ, it is called the midsagittal plane.
3. The dorsal plane is the plane that divides the body or an organ into the dorsal (back) portion and the ventral (belly) portion.

   Clinical Insight

   The dorsal plane is also referred to as the frontal or coronal plane because humans stand erect.

    

4. The transverse plane is the plane that divides the body or organ into the cranial (towards the head) and caudal (towards the tail) portions when on the body, or the distal and proximal parts when on a limb. The transverse plane cuts perpendicular to the length of the structure and produces images referred to as cross-sections.

Median and Sagittal Planes

The median plane divides the body into equal right and left halves. The sagittal planes divide the body into unequal right and left sides. For example, if a scan is being taken of the body, it could start from the median plane and continue taking images along the sagittal planes all the way to the outside of the body.

 

Body Cavities

A body cavity is a hollow space that houses organs and protects them. There are several cavities within an animal’s body. Each cavity contains a number of organs and plays a specific role in the functioning of the body.

The dorsal (posterior) cavity and the ventral (anterior) cavity are the two main cavities.

The dorsal and ventral cavities are each subdivided into smaller cavities:

The dorsal cavity has two main subdivisions:

• The cranial cavity houses the brain and the pineal and pituitary glands. It is protected by the bones of the skull and the cerebrospinal fluid.
• The spinal (vertebral) cavity encloses the spinal cord. It is protected by the spinal column and the cerebrospinal fluid.

The ventral cavity has can be divided into three subdivisions:

• The thoracic (chest) cavity is enclosed by the rib cage. It contains the heart and lungs, is protected by the ribs, and extends from the neck to the diaphragm.
• The abdominal cavity is the largest cavity in the body. It contains the organs of digestion and is between the diaphragm and the pelvic cavity.
• The pelvic cavity is caudal to the abdominal cavity. It contains the reproductive organs, urinary bladder, rectum, and anus.

Image Credits
(images are listed in order of appearance)

Archie planes by Kelly Robertson, NorQuest College. Used with permission.

Ozzie planes by Kelly Robertson, NorQuest College. Used with permission.

Running horse by Noel Asadin, Pixabay licence