SKELETON OF CHELONIA. 



615 



Similarly, the median pieces are the result of fusion between median 

 dermal bones and the neural spines of the vertebrae. The plastron 

 usually consists of nine dermal bones, and the three anterior pieces 

 perhaps represent clavicles and interclavicle (or episternum). 



The eight cervical vertebras have at most little rudiments of ribs, are 

 remarkably varied as regards their articular faces, and give the neck 

 many possibilities of motion. There are no lumbar vertebrae. 



The bones of the skull are immovably united ; there is only a lower 

 temporal arcade, formed by jugal and quadrato-jugal ; there are no 

 ossified alisphenoids, but downward prolongations of the large parietals 



sc 



FIG. 332. Pectoral girdle of a Chelonian. 



(?., Glenoid cavity ; SC., scapula ; P.C., procoracoid fused 

 to the scapula ; C., coracoid ; .C. t epicoracoid cartil- 

 age ; L., ligament. 



take their place ; neither presphenoid nor orbitosphenoids are ossified ; 

 there are no distinct nasal bones in modern Chelonians, their place 

 being taken by the prefrontals ; the premaxillae are very small ; there 

 are no teeth. 



There is no sternum. The pectoral girdle on each side consists of a 

 ventral coracoid and a dorsal scapula attached to the carapace. The 

 scapula bears an anterior process of large size, usually regarded as a 

 " precoracoid " or procoracoid. 



. The pelvic girdle consists of dorsal ilia attached to the carapace, 

 posterior ischia, and anterior pubes, with pre-pubic processes and an 

 epi-pubic cartilage. There is a pubic and an ischiac symphysis. 



The girdles originally lie in front of, or behind the ribs, but are over- 

 arched by the carapace in the course of its development. 



