, From what has been , 'stated it will be seen • that the cartilag,e cell or corpuscle is the first ' part formed that this ; cell generates others; that they form the lining of the primary tube; that the lining becomes the external lamina of an Haversian system : so that the parietes of the cell in the erobryo may be considered the element of -the lamime.
Again, the intercellular tissue found in the embryo forms the medium of connection be tween the cartilage cells or corpuscles, as they are called, between the primary tubes, where bone is developing, and lastly,becomesthe bond ,of union between the Haversian systems.
The foregoing description applies to the growth of the shaft of a long bone in the carti lage connecting it with the epiphysis.
The laws regulating the growth of the epiphysis in the cartilage which unites it to the shaft of the bone are but a slight modification of those which regulate the growth of the shaft. The cartilage corpuscles, however, here form small rounded groups, and ossification proceeds in the intercellular tissue around them, and the groups themselves eventually form a cavity, by which means the spongy head of the bone is formed. The flat bones are developed much as the long ones, the thin edges of these being tipped with cartilage, which developes its cells, and intercellular tissue.
A bone at the time of its development is of equal density through the whole diameter at the point where ossification is just perfected. The arrangement of compact and spongy, as seen in the various bones, is an after process which takes place gradually, and in relation to the individual bones of which the framework of the body is composed.
On considering the process of developement of bone, it will be apparent that the arrange ment of cells, intercellular tissue, &c. answers the purpose of giving a definite form and arrangement for the future nourishment of the bone, but that osseous tissue is independent of any particular form. Thus intercellular be comes osseous tissue, as does the tissue of the cells. I wish to lay stress upon this point, as it bears particularly upon the character of certain formations of bone in unnatural situations, or adventitious bone.
Ossification of permanent cartilage.—The cartilages of the larynx at an advanced age are liable to become ossified, and in such cases, as the formation of osseous tissue goes on but slowly, the process may be observed with ease. In this case the corpuscles do not develope others as in temporary cartilage where increase of size is required, but retain their usual appearance. While the osseous granules are
developed in the intercorpuscular tissue, at first but few of them are seen, and these spherical and isolated ; they soon, however, become numerous, and unite, thereby forming an osseous mass. The intercellular or intercorpuscular tissue having advanced in ossification, the cor puscles, or rather their parietes, pass through the same process, and by degrees the whole cartilage becomes converted into bone.
The formation of the individual granules is more readily observed in these cartilages than in any other situation. This form of ossifi cation establishes an interesting and explanatory link of connection between bone and the various osseous plates we find in abnormal situations. For in the latter the spherical granules appear, and these, at first few and isolated, and lying amongst the fibres of the tissue, rapidly in crease in number, unite, and form an osseous mass.
Osseous plates occur in various soft tissues as the result of deranged action, where in the healthy condition of the part they are not found, Thus we have osseous plates formed in the coats of arteries, in. the pleura, in the diaphragm ; also osseous masses in the uterus ; and some times in the muscular tissue and in the pla centa. These plates are all formed in the same manner, namely, by the developement of minute spherical osseous granules, which form into a mass, the shape of which is modified by the form of the tissue in which the develope ment occurs.
I have examined many of thdse formations and find them to be composed of true osseous tissue, but not true bone ; for they have not the definite Haversian systerns, which, formed of osseous tissue, constitute bone. But they have cavities scattered through them ; these, however, have no definite shape, but assume all kinds of irregular forms, and though they are no doubt necessary to the vitality of the mass, yet their action cannot be very perfect. Spiculm of osseous matter are sometimes met with in cancerous tumours, but here it is very rare to find an Haversian system. The osseous plates found in the dura mater are, however, true bone, and are developed like the flat bones. I am decidedly of opinion that these masses are endowed with vitality, and are not mere concretions as some have regarded them, though this vitality is of a low degree.