犬の顎関節軟骨並びに関節円板の発育に伴う分裂線の変化に就いて

Abstract

Splitting lines of the bone have been so far studied systematically in our Laboratory using various vertebrae animals from the view point of comparative anatomy. It has been revealed from these studies that the splitting lines of the bone represented the developmental phases of the bone through whole stages of animal's life of which the line system indicated the direction of growth and the irregular line mass was the direct sign of bone's functions. Assuming that the same situation with the compacta of the bone would hold true to the cartilage with respect to the role of splitting lines, the author undertook to make observation on the developmental changes of splitting lines as examined in the cartilage of articularis temporomandibularis and the discus articularis in dogs as a part of the studies on this line. The results were summarized as follows. 1) In this study various phases of the splitting lines as manifested in the cartilages of dogs with their growth through every stages of life were described. 2) The phases of the splitting lines as observed throughout the life cycle of animals can be summarized in two different categories, of which the one representing age changes of their morphological patterns, the other the same morphological changes but corresponding to ever increasing complexity of vital functions imposed on the bone. 3) The first stage (the embryo 60 days old) : This represents the primary stadium of development where only the irregular splitting lines are to be observed in these cartilages. The second stage (One to five months after birth) : This is period of vigorous growth of the animal where two basic line systems for future development are observed in these cartilages. One of the line systems runs vertically and the other runs from the middle of the inner side toward the antero-posterior margins, both being well developed. There are also observed two masses of irregular splitting lines, one representing the disturbance of growth direction, the other suggesting initiation of the masticatory function in the animal. The third stage (7 to 12 months after birth) : This is the time of growth completion where the line systems assume growth direction similar to those observed in the second stage and there appears irregular mass of splitting lines suggesting vigorous strain of masticatory function of the animal. The fourth stage (2 to 5 years old) : Here the animal completes its growth and its masticatory function represents one of the most vigorous functions of the body. This is reflected in these cartilages by alternating arrangement of the disturbed pattern of line system and the normal line system as result of its repair. 4) The line systems occurring in the fossa mandibularis and capitulum mandibulae run toward the same direction, indicating that the site receiving the most severe stress of mastication is the inner part of these cartillages.