OSSIFICATION is the formation of bone. This process occurs natu rally in the formation of the skeleton of man and the higher animals. [Bore, NAT. DIV.] It also occurs in the reproduction of new bone after the destruction or loss of old bones. [Fitacrenta] Ossification occurs as an unnatural or morbid process. It is observed in several tissues of the body. It is most frequent in the cartilages of the ribs, in which it almost constantly occurs in advancing years. In most persons bone begins to form in these parts after the fiftieth per; it sometimes commences between the ages of thirty and forty, but is often delayed to a much later period ; and Harvey relates that in the body of Thomas Parr, who died in his 153n1 year, the cartilages of the ribs were still flexible and soft. The change is generally earlier in wen than in women, and it affects the cartilage of the first rib sountr than the met.
Next to the cartilages of the ribs those of the windpipe are most liable to become osseous. Ossification of the cartilages of the ear, nose, and Eustachian tube Is, on the coutrary, extremely rare, and iu the few cases in which it occurs it is not particularly connected with old age. The cartilages of the moveable joints mover ossify.
The tendinous tissue is that which, next to the cartilaginous, is most subject to ossification. This change is not uncommon at the insertion of the tendons of muscles that are much exerted, and in the ligament of some fixed or scarcely moveable joints. Small pieces of bone are also not nnfrequently formed in the dues mater; and these are one of the sources of incurable epilepsy. Bone is also sometimes formed in the fibrous coats of the spleen and liver.
Ossification occasionally takes place in the false membranes produced by acute inflammation of the pleura, and more rarely in those of the pericardium; and it is a common process in the adhesions which form between the heads of bones exposed by ulceration of their cartilages, producing the most fixed kind of anchylosis of the joints.
A few remarkable cases are recorded of ossification of the muscles. There is a skeleton in the museum of the College of Surgeons in London, in which it has taken place to such an extent that nearly all the bones must have been immovably fixed by the transformation of the tissues by which, in the healthy state, they are moved. In equally
rare cases the crystalline lens, the vitreous humour, and some other parts, are found converted into bone.
In all these examples the material formed exactly resembles true bone in its minute structure and chemical composition. In other cases, as in ossification of the heart and arteries, the substance depo sited is composed of carbonate and phosphate of lime, as bone is, but its particles have no definite arrangement. That which is called ossification of the heart is not an affection of the proper substance of that organ, but of its valves, in which earthy matter is sometimes deposited, so as to render them stiff and unyielding, and destroy the pliancy which is necessary for the performance of their functions. A deposition of earthy matter in any part of the substance of the heart itself is very rare. [HEART, DISF.ASFS OF.] The disease named ossification of the arteries consists in the deposi tion of plates or rings of hard earthy substance in their middle elastic coats. This deposition is preceded by that of a peculiar soft or opaque yellow substance, which becomes gradually hardened. The deposition of this yellow substance in the large arteries is so common that it is very rare to meet with the body of an adult in whom it has not taken place to a greater or less extent ; and it not 'infrequently commeuces in early childhood. The change to earthy matter does not commonly take place before the thirtieth year, and is very general after the sixtieth. The roughness and irregularity in the circulation which it produces in the large arteries and the ulceration of their lining mem branes which often accompanies it, frequently produce serious symptoms. The same changes are frequent in the arteries of the legs, and the obstruction to the circulation which they produce generally gives rise, if life is sufficiently prolonged, to the affection called gangriena senilia. [ARTERIES, DISEASES OF.]