CARAPACE AND PLASTRON OF THE CHELONIAN REPTILES. 
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existing subjacent vertebral elements, long retain a very peculiar and distinct charac- 
ter of osseous texture, well-displayed in the development of the carapace and plastron 
of the land-Tortoises, which 1 next proceed to describe. 
Fig. 4 gives an outside view of the incipient carapace of a very young Testudo 
indica : fig. 5 shows an inside view of the same carapace, and figs. 6 and 7 similar 
views of the plastron of the same. 
The carapace is not quite three inches in length. On removing, after maceration, 
the well-developed epidermal scutella, the following ossified parts were seen : — the 
nuchal (cA), the pygal {py), and ten intervening neural plates (s i to s lo) ; mostly 
of a subquadrate form, but of irregular size, and with rounded angles and ill-defined 
outlines; the tenth plate (510) being insulated between the ninth (. sq ) and the pygal 
plate (py). On each side of the middle row of neural plates is a series of eight simi- 
larly-sized, triangular or rhomboidal plates (fig. 4,j9/i — jo/8),each of them marked on 
their outer surface with a triradiate linear impression formed by the junction of two 
costal scutella with one vertebral scutellum, or of one vertebral with two costal scu- 
tella; excepting the penultimate or seventh plate (ply). Around the border of the 
carapace are eleven pairs of marginal plates (m 1 — m n), exclusive of the nuchal (ch) 
and pygal (py) plates. The wide interval between the marginal and the incipient 
costal plates is occupied by the corium and its stratum of cartilaginous cells, sup- 
ported by the eight pairs of ribs of the carapace (fig. 5 , d 2 — d 9), by the first pair of 
short dorsal ribs (d 1), by the pair of shorter lumbar ribs, and by the rib-like upper 
and outer extremities of the hyosternals (hs) and hyposternals (ps), which ascend 
beyond the marginal plates. The extremities of the ribs do not as yet join the 
marginal plates. The nuehal plate, the ninth and tenth neural plates, the pygal 
plate, and all the marginal plates are independent osseous developments in the sub- 
stance of the derm : the other neural plates (s i — s s) are connate with the neural 
spines of the second to the ninth dorsal vertebrae inclusive, and the costal plates are 
similarly connate with the upper surface of the ribs of the same vertebrae at varying 
distances from their proximal ends. The first, second, fourth, sixth and eighth ribs 
of the carapace are continued from beneath the outer angles or apices of the corre- 
sponding costal plates (pi i, pi 2 , pi 4, pi e, pi s), but the third, fifth and seventh ribs 
of the carapace are continued from beneath the middle of that side of the correspond- 
ing, triangular costal plate which seems to form its base. 
The neural plates, the costal plates, and the marginal plates, whether attached to 
vertebral elements or detached, are lodged in the substance of the derm, and form a 
stratum of bones superficial to the ossified parts of the endo-skeleton. A strong argu- 
ment for regarding the costal plates as dermal ossifications rather than processes or 
continuations of the endo-skeletal elements, to which they are attached, may be drawn 
not only from the place of development of their cartilaginous basis or bed, but also 
from the period of their ossification ; and their relative position to the ribs with which 
they are connate. 
MDCCCXLJX. Y 
