loggerhead genes are still present in these populations today. Description The loggerhead sea turtle is the world's largest hard-shelled turtle, slightly larger at average and maximum mature weights than the green sea turtle and the Galapagos tortoise. It is also the world's second largest extant turtle after the leatherback sea turtle. Adults have an approximate weight range of , averaging around , and a straight-line carapace length range of . The maximum reported weight is and the maximum (presumed total) length is . The head and carapace (upper shell) range from a yellow-orange to a reddish brown, while the plastron (underside) is typically pale yellow. The turtle's neck and sides are brown on the tops and yellow on the sides and bottom. The turtle's shell is divided into two sections: carapace and plastron. The carapace is further divided into large plates, or scutes. Typically, 11 or 12 pairs of marginal scutes rim the carapace. Five vertebral scutes run down the carapace's midline, while five pairs of costal scutes border them. The nuchal scute is located at the base of the head. The carapace connects to the plastron by three pairs of inframarginal scutes forming the bridge of the shell. The plastron features paired gular, humeral, pectoral, abdominal, femoral, and anal scutes. The shell serves as external armor, although loggerhead sea turtles cannot retract their heads or flippers into their shells. Sexual dimorphism of the loggerhead sea turtle is only apparent in adults. Adult males have longer tails and claws than females. The males' plastrons are shorter than the females', presumably to accommodate the males' larger tails. The carapaces of males are wider and less domed than the females', and males typically have wider heads than females. The sex of juveniles and subadults cannot be determined through external anatomy, but can be observed through dissection, laparoscopy (an operation performed on the abdomen), histological examination (cell anatomy), and radioimmunological assays (immune study dealing with radiolabeling). Lachrymal glands located behind each eye allow the loggerhead to maintain osmotic balance by eliminating the excess salt obtained from ingesting ocean water. On land, the excretion of excess salt gives the false impression that the turtle is crying. The urea content is high in Caretta caretta tears. The skull is most easily distinguished from other sea turtles by having maxillae that meet in the mid-line of the palate. The portion of skull behind the eyes is