. Carnegie Institution of Washington publication. OSTEOLOGY. *5 may be supposed to represent the costal plates is the irregular border of the some- what expanded ribs. Of the other elements entering into the carapace of an emyd or a pleurodirid, the leatherback possesses only the nuchal bone. But the leatherback has a carapace peculiar to itself. This is composed of a layer of thin, polygonal bones which are buried in the thick skin of the animal. Of these bones there are 7 rows of larger ones, that appear in the living animal as so many sharp dorsal keels. One of these rows is along the midli
. Carnegie Institution of Washington publication. OSTEOLOGY. *5 may be supposed to represent the costal plates is the irregular border of the some- what expanded ribs. Of the other elements entering into the carapace of an emyd or a pleurodirid, the leatherback possesses only the nuchal bone. But the leatherback has a carapace peculiar to itself. This is composed of a layer of thin, polygonal bones which are buried in the thick skin of the animal. Of these bones there are 7 rows of larger ones, that appear in the living animal as so many sharp dorsal keels. One of these rows is along the midline; three run along each side. In front, this layer of mosaic-like bones overlies the nuchal. Smaller bones hll up the spaces between the rows. On the inferior side of the turtle there are 5 rows of similar bones, but the spaces between the rows are not so completely filled as on the upper side. Beneath the skin which supports these rows of bones there is a ring of elongated bones which represent the plastron of more normal turtles. These represent the epiplastra, the hyoplastra, the hypoplastic, and the xiphiplastra. The entoplastron is missing. All these bones are slender and thin, and they surround a vast Fig. 7.—Dermochelys coriacea. Greatly reduced. The cervical vertebra; differ in no important respect from those of Caretta, and the neck is equally short. The dorsals are ten in number and immovably joined to those in front and behind bv rough articular ends. The neural arches are moved forward, so that each articulates about equally with its own centrum and that in advance. They are somewhat expanded above, but do not come into contact with plates from the ribs. In fact, these plates are extremely vestigial. There are two sacral vertebra?, whose ribs articulate with the ilia; and there are about twenty caudals. The skull at first glance presents many resemblances to that of members of the Cheloniida-. The temporal roof extends backward as far as the occipital
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