854 ANATOMY [ANATOMY OF -.- -V; - ..- elongated spaces, called lacuna, are to be seen in con siderable numbers ; these lacunae, like the lamellae be tween which they are situated, have a concentric arrange ment around the Haversian canals. The lacunae, the lamellae, and the Haver- eian canal which they surround, are sometimes named a Haversian sys tem. From the ends and sides of any one of these lacunaa very minute branching canals, termed Ymafo cW/&,prOCeed,which Fl Q - 50. Transverse section through the com- L . .. pact tissue of tho shaft of a Ions bone. Tho penetrate the lamellO} and. Haversian canals, lamellae, lacunas, and anastomose with the canalicnli arc shown. canaliculi proceeding from adjacent lacunae, whilst the canaliculi, springing from the sides of those lacunae which lie nearest to the Haversian canal, open on the wall of the canal itself. The lacunae average in length inch, and their transverse diameter is about inch ; the canaliculi vary from TsoTnrth to TnrHo-th inch in diameter. When examined in a dried bono by transmitted light, the lacunae look like solid, black bodies, and the canaliculi seem to be processes branching off from them, hence they were erroneously called by the earlier observers bone-corpuscles. But if a little turpentine be added to the section, the fluid displaces the air which the lacunae and canaliculi contain in the dried bone, renders the part more transparent, and affords a satisfac tory demonstration that they are, in a macerated and dry bone, not solid bodies, but a minute system of spaces and anastomosing little canals; and that all those which lie in the same Haversian system not only freely communicate with each other, but, either directly or indirectly, with the Haversian canal which they surround. But a macerated and dried bone, such as one sees in museums and in articulated skeletons, and the structure of which has just been described, is a bone which has been deprived ^ of several soft tissues by the pro cess of putrefaction, which tis sues are of the utmost importance in the economy of the bone in the living animal. A living bone is a complex organ, and a macerated bone is only the skeleton of a Fjo 51 _ Longihldinal gcdion living bone. It IS essential, through the compact tissue of a therefore, in studying the struc- 5M2^X?*S"S ture of bone, that the attention steum P, into the Haversian i -I, .-IT , 1 , ,, canals II II. should not be limited to the ap pearances presented by the macerated bone, but that the arrangement and structure of its soft tissues should be con sidered. The soft tissues of a bone are the periosteum and its prolongations, the marrow, the minute masses of nucleated protoplasm which occupy the lacunae of the bone, the blood and lymph vessels, and the nerves. The Periosteum is a strong fibrous membrane which invests all the exterior of a bone, except where the encrusting cartilage is continuous with its articular j Ti T. i i i Fl - 52. Section t nrough the peri- eno. It IS Subdivided into two ostcum and compact tissue of layers : a, a firm external fibrous layer, consisting of bundles of connective tissue, which de cussate with each other in various directions, and amidst which a network of small blood-vessels is freely distributed prior to their young bone. S P, superficial fibrous layer of periosteum; D P, deeper cellular layer prolonged into H II, the wide Haversian canals ; V, a vessel of the periosteum entering a canal passage into the Havorsian canals ; &, a softer internal layer, which is especially well marked in young growing bones. This soft layer partly consists of very delicate connective tissue, in which rounded or oval cells are found, which give off slender processes at various points of their periphery, and partly of larger granular cells, which He next the bone itself. Processes of the soft inner layer are prolonged into the Haversian canals, in which, as Goodsir pointed out, a layer of cellular substance lies between the wall of the canal and its contained blood-vessel, so that these canals are not, as in macerated bones, empty passages, but are filled up by the blood-vessels and the cellular layer. The Marrow occupies the medullary canal of a long bone and the spaces in the cancellated tissue of bones generally. It occurs in two forms, red and yellow marrow. Red marrow is found in the bones of the foetus generally, and in the cancelli of the plate-like, short, and irregular bones at a more advanced period. It consists principally of large many-nucleated masses of protoplasm, the myeloid cells of Kolliker and Robin, lying in a very delicate areolar tissue, and supplied by a network of capillary blood-vessels. It contains little or no fat. Yel low marrow, again, is composed of fat cells lying in a delicate areolar tissue with accompanying blood-vessels. The areolar tissue, which supports the marrow cells, lines the medullary canal and cancelli, and is named the medul lary membrane, or the endosteum. In the fresh bone the lacunae are not empty spaces as in the macerated bone. They are filled up by nucleated clumps of protoplasm, and are therefore, as Goodsir was the first to show, the seats of little masses of nucleated cells, which cells are the true bone-corpuscles. The protoplasm of these cells is apparently prolonged into the canaliculi Hence the hard part of the osseous texture has within it a system of nucleated cells, some of which occupy the lacuna? and canaliculi, while others form a lining to the Haversian canals. The blood-vessels of a bone are abundant. It receives its arteries partly from the small arteries which ramify in the periosteum, the fine branches of which enter the Haversian canals, and form within them an anastomosing network of capillaries ; partly through a special artery which enters the nutrient canal in the bone, to be distri buted chiefly to the marrow; partly through small arteries which enter openings in the compact tissue near the articular extremities. The veins of bones are also abun dant. In the cancellated tissue they are large, and leave the interior of the bone partly through foramina situated near the articular ends, and partly by a vein which accom panies the artery that traverses the nutrient canal. In the plate-like bones of the skull the veins lie in distinct channels in the diploe, and in the bodies of the vertebrae the veins pass out through large holes in the posterior surface. Bones possess lymph-vessels, but their exact mode of arrangement has not yet been ascertained. Fine nerves have been traced into bones accompanying the arteries which enter the nutrient and Haversian canals. It is clear, therefore, that a bone, hard and dense though its texture seems to be, is yet hollowed out by spaces, passages, and canals which, under the several names of medullary canal, cancellated spaces, nutrient canal, Haversian canals, Haversian spaces, lacunae, and canaliculi, are occupied by blood-vessels or other soft tis sues. By the penetration of blood-vessels into the bone, blood is conveyed not only to the medulla, but into the very substance even of the compact tissue ; and there can be no doubt that the nucleated masses of protoplasm which occupy the lacunae and canaliculi, and line the Haversian canals, are, as Goodsir long ago pointed out, centres con cerned in the nutrition of the matrix substance of the
bone in their immediate neighbourhood. These cells.
