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.