The development of the human body; a manual of human embryology . directly, forming a suture. When, however, a portion of unmodified mesenchmyeintervenes between two cartilages, the mode of articula-tion of the bones formed from these cartilages will intermediate mesenchyme may in time undergo chon-drification and unite the bones in an almost immovablearticulation known as a synchondrosis (e. g., the sacro-iliac articulation); or a cavity may appear in the center ofthe intervening cartilage so that a slight amount of move- THE JOINTS. 213 merit of the two bones is possible, forming an
The development of the human body; a manual of human embryology . directly, forming a suture. When, however, a portion of unmodified mesenchmyeintervenes between two cartilages, the mode of articula-tion of the bones formed from these cartilages will intermediate mesenchyme may in time undergo chon-drification and unite the bones in an almost immovablearticulation known as a synchondrosis (e. g., the sacro-iliac articulation); or a cavity may appear in the center ofthe intervening cartilage so that a slight amount of move- THE JOINTS. 213 merit of the two bones is possible, forming an amphiarthro-sis (e. g., the symphysis pubis); or, finally, the intermediatemesenchyme may not chondrify, but its peripheral por-tions may become converted into a dense sheath of con-nective tissue (Fig. 110, c) which surrounds the adjacentends of the two bones like a sleeve, forming the capsularligament, while the central portions degenerate to form acavity. The bones which enter into such an articulationare more or less freely movable upon one another and the. Fig. 110.—Longitudinal Section through the Joint of the Great Toe in an Embryo of , Capsular ligament; i, intermediate mesenchyme which has almost disappeared in the center; p1 and p1, cartilages of the .first and second phalanges.—(Nicolas.) joint is termed a diarthrosis (e. g., the knee- or shoulder-joint). In a diarthrosis the connective-tissue cells near theinner surface of the capsule arrange themselves in a layerto form a synovial membrane for the joint, and portionsof the capsule may thicken to form special bands, the rein-forcing ligaments, while other strong fibrous bands, whichmay pass from one bone to the other forming accessoryligaments, are shown by comparative studies to be in 214 THE DEVELOPMENT OF THE HUMAN BODY. many cases degenerated portions of what were originallymuscles. In certain diarthroses, such as the temporo-mandibularand claviculo-sternal, the whole of the central portions ofthe i
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
