320 



CHELONIA 



CHAP. 



the pubic symphysis, and a smaller, longer, and narrow piece of 

 cartilage extends sometimes backwards from the ischiadic sym- 

 physis, as the so-called hypo-ischium. In the Pleurodira the 

 ends of the ilia, and those of the lateral processes of the pubes, 

 are much broadened and firmly ankylosed with the posterior 

 costal plates and with the xiphiplastron respectively. 



FIG. 65. Ventral view of the bony shell of Ckelone mydas, the Green Turtle, after 

 removal of the plastron (Fig. 66). The costal plates are marked by cross lines to 

 distinguish them from the ribs. C, coracoid ; Fe, femur ; Fi, fibula ; //, humerus ; 

 Ma.~i-Ma.12, marginal plates, some of which are fused together ; jVw, nuchal plate ; 

 PC, " precoracoid " ; R, radius ; Sc, scapula ; 7, V, first and fifth digits ; IX, Ninth 

 vertebra or first thoracic. 



The limbs are typically pentadactyle and complete, and are 

 most primitive in water-tortoises, e.g. Chelydra and Einys, in 

 which the carpus consists of the typical ten separate elements, 

 including the pisiform. In Tcstudo the centrale is fused with 

 the intermedium, and the first three distal carpals are also fused 

 together. In the marine turtles the limbs are transformed into 

 paddles, but all the bones retain their independence ; the pisiform 



