Median and sagittal plane

The body in anatomical position may be divided conceptually by planes. The median plane passes from the top to the bottom of the body and separates the left and the right sides of the body in equal halves.

Positions toward the median plane are called medial, and positions away from the median plane are called lateral. Hence ipsilateral refers to things on the same side, contralateral to something on the opposite side and bilateral to both sides.

A sagittal plane is any plane parallel to the median and hence the median plane is also called the midsagittal plane. A sagittal slice or section that is not on the median plane is also referred to as a parasagittal section.

Coronal plane

The frontal or coronal plane essentially separates the body into the forward half and the back half. This plane is perpendicular to the median and also passes from the top to the bottom along the long axis of the body. The term posterior refers to objects on the back half of the body, behind the coronal plane and the term anterior refers to objects in front of this plane.

Transverse plane

The horizontal or transverse plane is perpendicular to both of these planes and is the plane which divides the body into an upper and a lower half. Positions above the transverse plane are called superior, and positions below the transverse plane are called inferior. In comparative anatomy, superior may be called the rostral (beak) or cranial (head) end. Inferior may be referred to as the caudal or (tail) ends.

Planes in between these three are known as oblique planes.

Special cases

In the anatomical position, the penis is considered to be erect and pointing upwards, i.e. the dorsal side of the penis is what one would normally call its top side.

The tongue has a dorsal side which is facing upwards (the side that tastes and licks).

The perineum is a region of exception for obstetricians and gynecologists (OB/GYNs). OB/GYNs regard the perineal body in the perinuem to be an anatomical center and an important landmark. Several regions are discussed in spacial relation to the perineal body, deviating from the general terminology described above.

Note that the reclining body may be viewed correctly in terms of the anatomical position. Standing behind and at the head of a body, you will observe that the body's right arm with respect to your right arm is in the anatomically correct position. Likewise, the same with the body's left arm. This continues down the scope of the viewed body. Standing at the feet position when viewing the body, does not reveal the proper anatomical correct position.

Body cavities

The human body consists of the following cavities:

• dorsal body cavity

• cranial cavity, enclosed by the cranium and contains the brain

• vertebral canal, enclosed by the spinal column and contains the spinal cord

• ventral body cavity

• thoracic cavity, contains the lungs and heart

• abdominal cavity, contains the kidney, ureters and most of the digestive organs.

Human body cavities and membranes
Name of cavity			Principal contents	Membranous lining
Dorsal body cavity	Cranial cavity		Brain	Meninges
	Vertebral canal		Spinal cord	Meninges
Ventral body cavity	Thoracic cavity	Pleura cavities	Lungs	Pleurae
		Pericardial cavity	Heart	Pericardium
	Abdominopelvic cavity	Abdominal cavity	Digestive organs, spleen, kidneys	Peritoneum
		Pelvic cavity	Bladder, reproductive organs	Peritoneum

The cranial cavity is the relatively large space formed inside the skull. The brain occupies the cranial cavity, which is lined by the meninges and which contains fluid to cushion blows.

Eight cranial bones together form the cranial cavity: the frontal and occipital bones, and two each of the parietal, temporal, sphenoid and ethmoid bones.

The capacity of an adult human cranial cavity is 1,200-1,700 cm3.

The spinal canal (or vertebral canal) is the space in vertebrae through which the spinal cord passes. It is filled with cerebrospinal fluid. It was first described by Jean Fernel.

The thoracic cavity is the chamber of the human body (and other animal bodies) that is protected by the thoracic wall (thoracic cage and associated skin, muscle, and fascia). Structures within the thoracic cavity include:

• the lungs,

• the heart,

• the thoracic aorta,

• the main pulmonary artery and its branches,

• the thymus gland,

• the trachea and bronchi and

• the esophagus.

It contains the potential space called the pleural cavity and the mediastinum.

If the thoracic cavity is breached from the outside, as by a bullet wound or knife wound, a pneumothorax, or air in the cavity, usually results, often leading to one or both lungs collapsing and requiring immediate medical attention.

The abdominal cavity is the cavity of the human body (and other animal bodies) that holds the bulk of the viscera and which is located below (or posterior to) the thoracic cavity.

Organs of the abdominal cavity include the liver, gallbladder, spleen, pancreas, urinary bladder, small intestine and large intestine. The kidneys are located not in the abdominal cavity but behind it.

The abdominal cavity is lined with a protective membrane termed the peritoneum. The viscera are also covered, in the front, with a fatty layer called the omentum (or omental apron).