IX 



CARAPACE 



323 



means of several marginals. The connecting region is called the 

 bridge. In several tortoises, e.g. J^mi/s, the connexion with the 

 marginals is formed by ligaments only and remains movable. 

 In others, transverse, more or less perfect hinges are formed 

 across the plastron. A rather imperfect joint between the 

 hypo- and xiphi-plastrals develops with age in Testudo ihera. 

 In Gistudo and Cycl6my& a very effective hinge lies below the 

 hyo- and hypo-plastrals, just in front of the bridge; and the 

 anterior and posterior lobes of the plastron can be closed 



Neural Plate 



^;^rg^^^r— ; vEpiderm. 



>Cutl8. 



Fia. 68. — A, Diagrammatic transverse section through the shell of Testudo. On the 

 right side the horny shields have been removed, on the left are shown the neural, 

 costal, marginal, and pectoral shields. The bony dermal plates are dotted. Cap, 

 Capitular portion of rib ; <S^. C, position of spinal cord. B, Vertical section through 

 part of the shell, magnified and diagrammatic. B, Bony layer of the cutis ; L, 

 leathery layer of the cutis ; M, cells of the Malpighian layer ; p, star-shaped pig- 

 ment-cells ; so, stratum corneum, composing the horny shields. 



against the inner rim of the box, fitting tightly in Gistudo. 

 In Pyxis the front lobe only is movable. 



The carapace is composed of one median series, a right and 

 left lateral series of costal plates, and a series of marginals which 

 surround the whole. The median series consists of one large nuchal 

 plate, normally eight neurals and one to three supracaudal plates. 

 The characteristic feature of the neural plates is that they are 

 firmly fused with the broadened neural spinous processes of the 

 underlying vertebrae. The nuchal plate lies in front of the 

 first thoracic or ninth vertebra; it overlies the last cervical 

 vertebrae, with th% eighth of which it is connected by ligament 

 only ; but the posterior corner of the plate often fuses with the 

 spine of the ninth vertebra. In the Chelydridae, and still 



