Diploe: Definition, Flat Bones, Vascularization and Diploic Veins

It refers to the intermediate spongy tissue of a flat bone.

The diploe harbors and protects the red bone marrow found only in the bones of the hip, ribs, sternum, vertebrae, and the ends of long bones in adults.

Their fluid-filled spaces reduce the weight of most bones, allowing them to move more quickly and be supported by skeletal muscles. This structure is similar in the long bones to the medullary cavity.

The diploe is a soft and spongy material located between the inner table and the router table (the inner and outer bony plates) of compact tissue, contains bone marrow, and is called the diploe zone.

The microscopic study of the bone tissue distinguishes the compact bone component and the spongy bone component.

Although the constituent elements are the same in the two types of bone substance, they are distributed differently according to the kind and macroscopic aspect.

In the compact bone substance, the sheets of bone tissue are firmly joined by their faces, without free space interposed. For this reason, this type is more dense and complex.


In the spongy bone substance, the bony laminae are more irregular in shape and size; they are arranged to leave between them spaces or gaps that communicate with each other and contain marrow.

Flat bones

Bones can be classified according to the shape of long, short, flat, irregular, and sesamoid bones.

The bones are made up of several different tissues: bone, cartilaginous tissue, dense connective, epithelial, adipose, nervous, and various blood-forming tissues.

The spongy tissue in the flat bones is central. Both sides of the bone are covered by compact tissue, such as scapula, clavicle, parietal, frontal, occipital, temporal, etc.

In this type of bone, the relationship between length and width over thickness predominates.

The primary function of flat bones is to protect organs, and they have venous vessels of bone tissue, where hematopoiesis, or the formation of red blood cells, is carried out in the blood.

The spongy substance between the two layers of porous substance in flat bones is called diploe.


This intermediate tissue between both laminae in the bones of the skull has a more trabecular and vascular behavior than the joint spongy tissue. The bones are highly vascularized.

The diploic veins are veins located within the diploe of the cranial vault.

The diploic veins that occupy channels in the diploe of the bones of the skull are large and exhibit at irregular intervals bag-type dilatations; their walls are thin and formed by an endothelium that rests on a layer of elastic tissue.

As long as the bones of the skull are separable from one another, these veins are confined to particular bones; but when the sutures are erased, they join together and increase in size.

They communicate with the meningeal veins, the paranasal sinuses of the dura, and the pericranium veins.

They consist of the frontal, which opens towards the supraorbital vein, and the superior sagittal sinus.

The anterior temporal, confined mainly to the frontal bone, open to the sphenoparietal sinus and one of the deep temporal veins through an opening in the large wing of the sphenoid.

The posterior temporalis is located in the parietal bone. It ends in the transverse sinus through an opening in the mastoid angle of the parietal bone, or the mastoid foramen.

The occipital, the largest of the four, is confined to the occipital bone and opens either externally in the occipital vein, internally in the transverse sinus, or in the confluence of the paranasal sinuses.

The diploic veins pass within the diploe of the cranial vault and are connected due to the veins issuing from the dural venous sinuses and the external venous drainage of the skull.

Four different diploic veins are named after the areas of the skull where they are found:

Vena diploica frontal:

In the diploe of the frontal bone, the frontal diploic vein drains inward into the superior sagittal sinus and outwards into the supraorbital vein.

Vena diploica temporal anterior:

The anterior temporal diploic vein is located mainly inside the frontal bone and the parietal bone, draining into the sphenoparietal sinus and outward into the deep temporal vein.

Vena diploica temporal posterior:

The posterior temporal diploic vein, located in the diploe of the parietal bone, connects the superior sagittal sinus with the transverse sinus.

Vena diploica occipital:

The posterior temporal diploic vein, located in the diploe of the parietal bone, connects the superior sagittal sinus with the transverse sinus.

The diploic occipital vane, located in the diploe of the occipital bone, drains inwards at the confluence of the paranasal sinuses or the transverse sinus and outwards in the occipital vein.

The occipital diploic vein is the largest of these four.

The diploic veins create a direct connection between the external venous drainage of the skull and the internal paranasal sinuses.

Infections can spread through the connections and reach the dural venous sinuses; at this level, pathogens can cause, for example, meningitis.