[88] See H.G. Seeley, On the Organisation of the Ornithosauria, _Journ. Linn. Soc._ (Zoology) vol. XIII. p. 84. K.A. Zittel, Ueber Flugsaurier aus dem lithographischen schiefer, _Palaeontograph._ XXIX. p. 49. CHAPTER XIV. THE SKELETON OF THE GREEN TURTLE. (_Chelone midas._) The most striking feature as regards the skeleton of the Turtle is that the trunk is enveloped in a bony box, the dorsal portion of which is called the =carapace=, while the ventral portion is the =plastron=. I. EXOSKELETON. _a._ The =epidermal exoskeleton= in the Green Turtle as in all other Chelonia except _Dermochelys_, _Trionyx_ and their allies is strongly developed, its most important part consisting of a series of horny =shields= which cover over the bony plates of the carapace and plastron but do not at all correspond to them in size and arrangement. The shields covering over the =carapace= consist of three rows of larger central shields,--five (=vertebral=) shields being included in the middle row and four (=costal=) in each lateral row,--and of a number of smaller =marginal= shields. Of the marginal shields, that lying immediately in front of the first vertebral is termed the =nuchal=, while the two succeeding the last vertebral are called sometimes =pygal=, sometimes =supracaudal=; the remainder are the marginal shields proper. The epidermal covering of the =plastron= consists principally of six pairs of symmetrically arranged shields, called respectively the =gular=, =humeral=, =pectoral=, =abdominal=, =femoral=, and =anal=, the gular being the most anterior. In front of the gular shields is an unpaired =intergular=, and the shields of the plastron are connected laterally with those of the carapace, by five or six pairs of rather irregular =infra-marginal= shields. Smaller horny plates occur on other parts of the body, especially on the limbs and head. Two other sets of structures belong also to the epidermal exoskeleton, viz. (_a_) horny =beaks= with denticulated edges which ensheath both upper and lower jaws, (_b_) =claws=, which as a rule are borne only by the first digit of each limb. Sometimes in young individuals the second digit is also clawed. _b._ The =dermal exoskeleton= is strongly developed, and is combined with endoskeletal structures derived from the ribs and vertebrae to form the carapace. The =Carapace= (fig. 36) consists of a number of plates firmly united to one another by sutures. They have a very definite arrangement and include: (_a_) the =nuchal= plate (fig. 36, 1), a wide plate forming the whole of the anterior margin of the carapace. It is succeeded by three series of plates, eight in each series, which together make up the main part of the carapace. Of these the small (_b_) =neural plates=[1] (fig. 36, A, 2) form the middle series. They are closely united with the neural arches of the underlying vertebrae;