The diploic veins are large, thin-walled valveless

vein Veins () are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and feta ...

s that channel in the diploë between the inner and outer layers of the

cortical bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, an ...

in the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, first identified in dogs by the anatomist Guillaume Dupuytren. A single layer of endothelium lines these veins supported by elastic tissue. They develop fully by the age of two years. The diploic veins drain this area into the dural venous sinuses. The four major trunks of the diploic veins found on each side of the head are frontal, anterior temporal, posterior temporal, and occipital diploic veins. They tend to be symmetrical, with the same pattern of large veins on each side of the skull. It has been suggested that the venous patterns they form resemble fingerprints in their individuality.

Types of diploic veins

The ''frontal'', which opens into the supraorbital vein and the superior sagittal sinus. The ''anterior temporal'', which is confined chiefly to the

frontal bone In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...

, and opens into the sphenoparietal sinus and into one of the deep temporal veins, through an aperture in the great wing of the sphenoid. The ''posterior temporal'', which is situated in the

parietal bone The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...

, and ends in the

transverse sinus The transverse sinuses (left and right lateral sinuses), within the human head, are two areas beneath the brain which allow blood to drain from the back of the head. They run laterally in a groove for transverse sinus, groove along the interior ...

, through an aperture at the mastoid angle of the

or through the mastoid foramen. The ''occipital'', the largest of the four, which is confined to the

occipital bone The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lob ...

, and opens either externally into the occipital vein, or internally into the

or into the confluence of the sinuses (torcular Herophili). It has been noted that "The tunnels formed by diploic veins are among the few known skeletal markers of soft tissue alteration".

Functionality

The function of diploic veins is unclear. One function that has been suggested is brain cooling. In this account, venous blood from the scalp, cooled by its sweat glands, passes to the pachymeningeal veins by way of the diploic venous system. The diploic venous system in modern humans is more complex and developed than in chimpanzees and this has been suggested to be a consequence of the greater need of the human brain for such cooling.

References

Veins of the head and neck {{circulatory-stub