Gray's Anatomy

In the long bones, numerous apertures may be seen at the ends near the articular surfaces, some of which give passage to the arteries referred to; but the greater number, and these are the largest of them, are for the veins of the cancellous tissue which run separately from the arteries.

The veins emerge from the long bones in three places (Kölliker). 1. By a large vein which accompanies the nutrient artery; 2. by numerous large and small veins at the articular extremities; 3. by many small veins which arise in the compact substance.

Those of the compact tissue are derived from a close and dense network of vessels, which ramify in a fibrous membrane termed the periosteum, which covers the surface of the bone in nearly every part.

These are the bone cells, discovered by Virchow. The lacunæ are oval flattened spaces, lying parallel to the direction of the lamellæ. The canaliculi issuing from them are extremely minute, their diameter ranging fromtoof an inch.

We have already said, that the dark spots seen in and between the lamellæ, arranged in concentric circles around the Haversian canals, are the lacunæ.

According to Dr. Sharpey, the lamellæ, in structure, consist of fine transparent fibres decussating each other, so as to form a delicate network, the fibres apparently coalescing at their point of junction. The lamellæ are perforated, in certain situations, by bundles of fibres which penetrate them in a more or less oblique direction, serving to securely approximate the several plates.

The lamellæ are also perforated by numerous minute apertures placed at regular distances apart, which are, probably, transverse sections of the canaliculi. In this fibrous basis of the lamellæ, the inorganic elements of bone are intimately united.

These spaces may exist in various conditions: in some, the process of absorption is evidently going on; in others, the spaces are lined by newly-formed lamellæ which fill up the peripheral portion of the space; in others, the lamellæ fill in the whole of the space, leaving a Haversian canal in the centre.

Besides the lamellæ surrounding the Haversian canals, some are disposed parallel with the outer and inner surfaces of the bone; these are termed circumferential lamellæ, and may be considered as concentric with the medullary canal. Others, again, penetrate between the Haversian systems; these are termed interstitial lamellæ. Each Haversian canal, together with its concentric lamellæ of bone, lacunæ, etc., is called an Haversian system, the blood-vessel contained in the central canal being the source of nutrition to the lamellæ which surround it.

By this means, the Haversian canals establish a free communication between the bloodvessels of the periosteum, and those of the medullary membrane.