In generalized emyid turtles such as _Clemmys_ there are no movable shell parts. The plastron is joined to the carapace by the sutures of the bridge. A long stout process, the axillary buttress, arises on each side from the hyoplastron and articulates with the tip of the first costal. A similar process, the inguinal buttress, arises from the anterior part of each of the hypoplastral elements and meets the sixth costal on each side. The buttresses form the anterior and posterior margins of the bridge. It is clear that movement of the plastron in many emyids is mechanically impossible because of the bracing effect of the buttresses. In _Terrapene_ the movable articulations of the shell are neither structurally nor functionally developed in juveniles. Adults of _T. ornata_ have highly modified bony buttresses on the plastron that are homologous with those in more generalized emyids. The inguinal buttresses are low and wide, and have a sheer lateral surface forming a sliding articulation with the fifth and sixth peripheral bones of the carapace. The axillary buttresses are reduced to mere bony points near the posterolateral corners of the forelobe and do not articulate directly with the carapace (Figs. 15 and 16). The fifth peripheral bone, constituting the lowest point of the carapace, has a medial projection that acts as a pivoting point for both lobes of the plastron; the roughened anterior corners of the hind lobe articulate with these processes. The roughened posterior corners of the forelobe of the plastron likewise articulate with these processes. The posterior process or "tail" of the entoplastron extends to, or nearly to, the bony transverse hinge. In juveniles that have been cleared and stained, the homologues of the parts that are movable in adults are easily identifiable; the proportions of these parts and their relations to one another are, however, much different. In juveniles (Figs. 18 and 19) the buttresses are relatively longer and narrower, and are distinct--more nearly like those of generalized emyids than those of adult _T. ornata_. The buttresses enclose a large open space, which in adults is filled by the fifth peripheral. The hyoplastral and hypoplastral bones are in contact only laterally. They are firmly joined by bony processes; the interdigitating nature of this articulation contrasts with its homologue in the adult, the point where the roughened corners of the forelobes and hind lobes meet. The fifth peripheral in juveniles (Fig. 19) lies dorsal to this articulation. The position of the future transverse hinge corresponds to a line passing through the articulations of the hyoplastra and hypoplastra. The tail of the entoplastron ordinarily extends posterior to this line in juveniles.