The costoneural fontanelles are nearly closed in individuals of the 70 millimeter (plastron length) class and seldom remain open after a length of 80 millimeters is attained (Fig. 14). Of the costoperipheral fontanelles, the anterior one (between first rib and nuchal bone) closes first and the posterior one (between last rib and pygal bone) last. It remains open in some turtles in which the plastron is longer than 100 millimeters. The remaining costoperipheral fontanelles close in varying sequence but those in the area of the bridge (nos. 2 to 5), where there is presumably greater stress on the shell, close sooner than the others. The plastral fontanelles are closed in most specimens of the 90 millimeter (plastron length) class; the anteromedian fontanelle closes first. The meager covering of the fontanelles makes juvenal turtles more susceptible than adults to many kinds of injuries and to predation. _Movable Parts of the Shell_ Parts of the shell that are more or less movable upon one another and that function in closing the shell are found in several families of Recent turtles. African side-necked terrapins of the genus _Pelusios_ have a movable forelobe on the plastron. Kinosternids have one or two flexible transverse hinges on the plastron. In the Testudinidae the African _Kinixys_ has a movable hinge on the posterior part of the carapace and _Pyxis arachnoides_ of Madagascar has a short, hinged, anterior plastral lobe. Certain trionychid turtles, such as _Lissemys_, utilize the flexible flaps of the carapace (the flaps of some species are reinforced with peripheral bones) to close the shell. Movable shell-parts of turtles are, in general, protective in function; they cover parts of the soft anatomy that would otherwise be exposed. A hinged plastron, capable of wholly or partly closing the shell, occurs in six genera of the family Emyidae (see introduction). In these emyids the plastron is divided into two lobes, which are joined to each other by ligamentous tissue at the junction of the hyoplastral and hypoplastral bones; externally, the hinge occurs along the seam between the pectoral and abdominal laminae. This junction forms a more or less freely movable hinge in adults. The plastron is attached to the carapace by ligamentous tissue. Both lobes of the plastron or only the buttresses of the hind lobe may articulate with the carapace. The former condition obtains in _Emys_ and _Emydoidea_; the latter more specialized condition is found in _Terrapene_.