The origin and early development of the clavicle in the quail (Coturnix c. japonica)

Development of the clavicle in the Japanese quail is described in detail and evidence presented for its development in cartilage. Chondroblast cells and the chondroitin sulphate of the cartilage matrix are identified using a toluidine blue‐silver impregnation technique. It was found that the cartilage phase is transitory and is rapidly obliterated by the ossification stage. An initial invasion of the cartilage by osteoblasts is followed by deposition of granules of calcified material scattered randomly in the cartilage in the region of the ramus. In the hypocleideum, however, the calcification is initially perichondral, as seen in the initial ossification of the coracoid, but later resembles that of the clavicular ramus, in being random. The pattern of chondrogenesis and'osteogenesis seen in the clavicle suggests an acceleration of the normal process of endochondral ossification with an abbreviation of the cartilage phase. This study reveals that the development of the clavicle in this bird is not dissimilar (as is generally accepted) to that of other skeletal elements of the primary pectoral girdle.