ORDER CHELONIA. 



:o8 3 



opisthotic bone (fig. 1024). The dentary bones of the mandible 

 are generally fused together ; the postorbital is welded with the post- 

 frontal, and usually the prefrontal with the nasal ; while the supraoc- 

 cipital is prolonged backwards. There is no transverse bone. The 

 palate is completely closed by the junction of the pterygoids with 

 the basisphenoid, and often with one another (fig. 1 o 1 7 bis). In all 

 existing forms, teeth are absent, and the trenchant jaws ensheathed in 

 horn. Each rib articulates at the junction of two vertebrae ; there are 



Fig. 1006. — Ventral aspect of the skeleton of a young Loggerhead Turtle (Thalassochelys 

 caretta), with the plastron removed. Much reduced. The coracoid and precoracoid of opposite 

 sides are here represented as widely separated from one another. (After Owen.) 



no ribs in the cervical region, and no transverse processes to the dor- 

 sal vertebrae. The vertebrae may have proccelous, opisthoccelous, or 

 amphiccelous centra in different parts of the column of the same in- 

 dividual. In the pectoral girdle (fig. 1008), which is situated within 

 the ribs, the coracoid is the widest of the three cartilage bones ; and 

 the coracoid and precoracoid of opposite sides are respectively con- 

 nected in the middle line by ligamentous tissue only. The con- 

 nection between the scapula and precoracoid is short, and there is 



