Histogenesis of bone marrow: a cytological and morphological study of osteogenesis

Chondrogenesis and osteogenesis are growth manifestations of multipotent primitive connective tissue.The cells vthich engender these two processes, have the same developmental origin, evincing activities which diverge as growth proceeds.Cartilage formation precedes and is independent of osteogenesis, occurring by an ontogenetic development of the primitive connective tissue cells, the essential change in which is the appearance of a chondromucin matrix, as an exoplasm.Bone formation is initiated by a later growth impulse of a different order. It consolidates the growth registered by the cartilage, thereby fulfilling its ultimate aim; the development of an entirely new structure, the secondary nature of which is apparent, both phylogenetically and ontogenetically .The primitive connective tissue cells of the chondrogenetic areas in the course of growth form the chondroblasts of cartilage, the fibroblasts of the perichondrium or periosteum, the osteoblasts and osteoclasts of osseous tissue, and the haemoblasts and reticular cells of marrow. They persist and extend by growth. When the cartilage model is corn pleted they occupy a position between it and the perichondrium. It is in this region that the osteoblasts concerned with circumferential growth of the diaphysis are evolved.Invasion of the cartilage model takes place by proiferation of young connective tissue cells, the movement of the tissue occurring as a growth extension. In the diaphyses, they rapidly form a zone of syncytial tissue which continually replaces the dead hypertrophic hypertrophie cells at the ossification line. This zone is the site of formation of the endochondral osteoblasts and osteoclasts, the endothelial cells of the growing capillaries, and the primitive blood cells, "the haemoblasts ".In the epiphysis, the primitive connective tissue cells grow into the cartilage mass, along channels which develop by solution of the chondromucin. When the cartilage of the epiphysis prepares itself for osseous replacement, the undifferentiated connective tissue, which has made its way to the site of the cartilage activity, proceeds as in the diaphysis with the development of osteoblasts in situ.Osteoblasts are specialised cells which evolve only by the ontogenetic development of primitive connective tissue cells. They develop in accordance with growth requirements, at or near the site of their activity from pre-existing tissue, whether they engage in sub-periosteal or endochondral bone disposition. In whatever situation they arise, the stem cell is the same, and the transition process identical.Osteoblasts undergo a cytomorphosis during the deposition of ossein and form branched cells, which become embedded in the bone substance. The branched cells are the bone corpuscles. Bone substance is secreted by the processes, which pass out from every aspect of the cell body and anastomose with similar ' processes from neighbouring cells. The amount of ossein secreted by a bone corpuscle depends upon the extent of the ramification of the branched protoplastic processes.Osteoclasts arise at the ossification line, and subperiosteally, by fusion of the primitive cells. They are osteolytic in function connectiv Disintegration occurs either by structural degeneration or by splitting up into single cells which mingle with the young connective tissue elements of the reticular tissue.Growth in length of the diaphysis of a long bone is entirely effected by cartilage increments. Growth in diameter is achieved only by osseous increments. Epiphyseal growth is achieved solely by the interstitial expansion of the cartilage.Periosteum and perichondrium are one and the same structure, developed from the peripheral primitive connective tissue cells of the chondrogenetic area. It is a fibrous tissue membrane; the fibroblasts are finally differentiated and shew no tendency to revert to undifferentiated connective tissue cells. In no way associated with bone deposition, it affords an attachment for neighbouring structures, and serves as a "limiting" membrane for osteoblastic activity