12 CRYPTODIEA. 



axillary buttress of the plastron ; this first rib is considorabl)' more 

 ehjiigate in the Chelydridie. From the second to the eighth ver- 

 tebra inclusive the centra, which have tlatteiied articulary faces, 

 are connected by suture with the neural arches, which expand into 

 bony (neural) plates alternating with the centra, and with strong 

 ribs which, at a short distance from their attachment (between 

 centrum and arch), expand into large bony (costal) plates suturally 

 united with the neural plates. The neural spine may be low or 

 obsolete, or more elevated, in which case it is reduced to a narrow 

 septum pierced with fontanelles ; the latter being special to adult 

 specimens of the genus Testudo. The " capitular" extremity of the 

 second rib articulates between the first and second centra, and so do, 

 as a i-ule, the third and fourth ; but tlie following generally shift 

 back so as to articulate with the middle of the posteiior centra. In 

 very old specimens it not unf'requenlly happens that the costal 

 " capitula " become atrophied or disappear altogether. The tenth 

 vertebra forms the counterpart of the first : the centrum is very 

 short, with a posterior condyle, and a short rib which may (in 

 Chehjdra and Plutysternum) abut on the eighth rib in the same 

 manner as the first does on the second ; but, as a rule, it differs 

 little in appearance from the penultimate dorsal and the following 

 sacral. With the exception of the first and hindermost, the centra 

 are longer than broad : they may be flattened infcriorly (second 

 vertebra of most Emydines, second to fourth or fifth of Chelydridpe), 

 feebly compressed, or strongly compressed and forming a keel {Der- 

 mak-mjis, BaUKjur, Chrijsemy?:^ Testudo). 



In front of the series of neural plates is a large plate, the nuchal, 

 situated above the first dorsal vertebra : this plate, which is present 

 in all Chelonians, is a cartilage bone, developed simultaneously with 

 the neural jijatcs; the fact that it is connected, by ligament, with 

 the last cervical vertebra, and that it assumes on each side, in the 

 Chelydridic, the form of a rib, suggests the possibility of its repre- 

 senting, in part at least, the modified ribs of the last cervical. Such 

 rib-like processes are also present, well developed in the young and 

 shorter in the adult, in the Dermatemydidic and Cinosternidae, 

 Tinderlying the first or first two marginals ; in i'hehjdra and Ma- 

 crodemmys the rib-like process extends to below the third marginal 

 and abuts on the distal end of the first costal. A mere indication 

 of this process is found in some young specimens of Emys orbicularis 

 and other Emydines. The nuchal is six-sided and broader than 

 long *. 



There are normally eight neural })lates. In a few genera, how- 

 ever (Dcrrndtony.'i, iSidurotypun, Cinosttrmnn, Ciatudo), the series is 

 reduced by one to three of the hindermost, and the corresjjonding 

 last or last two or three pairs of costal plates meet in a suture on 



* A fossil Chdiidra (C7/('lt/(lroji.'ii.<, C. VAera) has been describud as liaving 

 two liUL-bals; but ll;at sucb is due to an amiiiialoiis transverse division, 1 have 

 little doubt. 



