TORTOISES AND TURTLES. 565 



tending into the tissue between neighbouring spinous processes, and 

 superficially up to the tissue which has differentiated into the thin 

 layer of connective tissue below the scales. 



The ventral shield or plastron consists of dermal bones; according 

 to some, three anterior pieces represent clavicles and interclavicle. 



The cervical vertebrae 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 vertebrce. 



The bones of the skull are immovably united ; there are no ossified 

 alisphenoids, but downward prolongations of the large parietals take 

 their place ; neither presphenoid nor orbitosphenoids are ossified ; there 

 are no distinct nasal bones in modern Chelonians ; the premaxilloe are 

 very small ; there are no teeth ; there is a complete bony palate formed 



FIG. 192. Internal view of skeleton of Turtle. (From 

 Edinburgh Museum of Science and Art.) 



H, humerus ; Sc, scapula, running dorsally ; c, coracoid ; e.c, 

 epi-coracoid ; p.c,, pre-coracoid ; P, pubes ; z7, ilium, running 

 dorsally ; Is, ischium ; F, femur. 



in great part from the junction of the pterygoids with the basisphenoid 

 and with one another. 



There is no sternum. 



The pectoral girdle on each side consists of a dorsal scapula attached 

 to the carapace, a ventral coracoid bearing terminally a small epicora- 

 coid, and anterior to the coracoid a " precoracoid." 



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

 terior pubes fused in a symphysis, and posterior ischia similarly fused. 



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

 arched by the carapace in the course of its development. 



