208 



1095. The "left radius, ulna, carpal, metacarpal and phalangeal bones of the Testudo 

 greeca. Hunterian. 



1096. The left tibia, fibula, tarsal, metatarsal and phalangeal bones of the same Tes- 

 tudo ffreeca. Hunterian. 



Preparations illustrating the development of the carapace and plastron of the 



Chelonia, 



1097. The carapace of a young Tortoise (Testudo). 



The bodies. and neural arches of the vertebra have been removed from the carapace, 

 leaving only the ribs and the incipient expanded plates attached to these and to the neural 

 spines, together with the marginal plates. The neural plates are of a subquadrate form, but 

 of irregular size, and with rounded angles and ill-defined outlines ; the tenth plate being in- 

 sulated between the ninth and the last or pygal plate. On each side of the middle row of 

 neural plates is a series of eight similarly-sized, triangular or rhomboidal plates, 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 scutella ; 

 excepting the penultimate or seventh plate. Around the border of the carapace are eleven 

 pairs of marginal plates, exclusive of the nuchal and pygal plates. The wide interval between 

 the marginal and the incipient costal plates was occupied by the corium, supported by the 

 eight pairs of ribs of the carapace, by the first pair of short dorsal ribs, by the pair of shorter 

 lumbar ribs, and by the rib-like upper and outer extremities of the hyosternals and hypo- 

 sternals, which ascend beyond the marginal plates. The extremities of the ribs do not as 

 yet join the marginal plates. The nuchal plate, the ninth and tenth neural plates, the pygal 

 plate, and all the marginal plates are independent osseous developments in the substance of 

 the derm : the other neural plates are connate with the neural spines of the second to the 

 ninth dorsal vertebrse inclusive, and the costal plates are similarly connate with the upper 

 surface of the ribs of the same vertebrse 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 corresponding costal plates, but the third, fifth and seventh ribs 

 of the carapace are continued from beneath the middle of that side of the corresponding tri- 

 angular costal plate which seems to form its base. 



A strong argument for regarding the costal plates as dermal ossifications rather than pro- 

 cesses or continuations of the endo-skeletal elements, to which they are attached, may be 

 drawn not only from their place of development, but also from the period of their ossifica- 

 tion ; and their relative position to the ribs with which they are connate. 



The uniformly slender pleurapophyses are ossified nearly throughout their whole length 

 before the ossification of the costal plates, which have usually been regarded as their ex- 



