12 ANATOMY OF A CHELONIAN. 



vertebrae from the second to the ninth, inclu- 

 sive ; the Pygal Plate. 



b. On each side of the above middle row are eight 

 costal plates, formed by expanded ribs attached 

 to the dorsal vertebrae from the second to the 

 ninth. In all except old full-grown specimens 

 the outer ends of the costal plates are not fully- 

 ossified ; and, accordingly, spaces filled only by 

 cartilage are then left between each one and its 

 successor. 



c. The Marginal Plates, eleven on each side, ex- 

 tend from the nuchal to the pygal. From the 

 second to the fifth, inclusive, they reach ven- 

 trally to articulate with the plastron. 



U. On the inner (ventral) aspect of the carapace, note 

 the projecting centra of the Dorsal Vertebrae. The most 

 anterior is attached dorsally to the nuchal plate ; the 

 eight succeeding ones bear, dorsally, the expanded neu- 

 ral spines already seen on the exterior of the carapace 

 as the neural plates. 



a. The first dorsal vertebra is comparatively short 

 and thick, and bears anteriorly a pair of large 

 stoutprezygapophyses {anterior articular processes), 

 which slope downward and forward. 



b. The centra of the succeeding dorsal vertebras, 

 back to the eighth, are considerably elongated 

 in the antero-posterior axis, and compressed 

 from side to side. Each has flattened ends, and 

 between each pair lies a thick plate of cartilage, 

 except in quite old specimens in which the 

 intervening cartilage is much thinner. The 

 whole set of dorsal vertebral centra, with these 



