Objective The purpose of this study was to investigate the distribution of collagenⅠ,Ⅱ,Ⅹ,alkaline phosphatase (ALP) and their roles during initiation of condylar cartilage of the fetal mouse.Methods Coronary sections of mandible of mouse embryo aged from14thto 18thdaywere studied under lightmicroscope after stained by immunohistochemical methodwith an- tibody of typesⅠ,Ⅱ,Ⅹcollagen and ALP.Results On the 14th day ofmouse embryo, itwas found thatmesenchymal cells con- densation continuous with the periosteum. TypeⅠcollagen and ALP were positive behind the terminal of the ossifying mandibular periosteumwhere future condylarwill form. On the 15th day, positive staining for typesⅠ,Ⅱcollagenwas found in mesenchymal cells around hypertrophic cells and typeⅩcollagenwas detected in hypertrophic cells. ALPwas positive in bothmesenchymal cells and hypertrophic cells. On the 16th day, typeⅠcollagen was observed from periosteal osteogenic cells and mesenchymal cells of the fibrous cell layer to the upper hypertrophic cell layerwhileTypeⅡcollagenwas restricted fromthe lower polymorphic cell layer to the bottom of the hypertropic cell layer. TypeⅩcollagenwas positive in the hypertrophic cell layer. ALPwas positive in perios- teal osteogenic cells and hypertrophic chondral cells, but not in the polymorphic cell layer.Conclusion Development of condylar cartilage is different from that of limb bone. TypesⅠ,Ⅱ,Ⅹcollagen are expressed in the condylar chondrocyte on the early stage of endochondral ossification. The histology evidence supports the conjecture that condylar cartilage is derived from differentiated mesenchymal cells of the preperiosteum or periosteum of the mandible where ALP is positively expressed.
