406 



CHELONIA. 



first differs from the others ; it is procoelous, it has a pair of prezygapo- 

 physes, its spine is not connected to a neural plate, and its rib has no costal 

 plate but is connected with the costal of the next vertebra. The neural 

 arch of this vertebra occupies only tlie anterior part of its centrmu. The 

 neural arch of the second thoracic overlaps the centrum of the first, occupy- 

 ing the anterior half of 

 its own and the posterior 

 half of the preceding cen- 

 trum. This applies to the 

 next eight thoracic verte- 

 brae, and also to their ribs 

 which are carried for- 

 wards with the arch 

 and articulate, not only 

 with their own centrum 

 and arch, but also with 

 the centrum and arch of 

 the preceding vertebra. 

 In the tenth vertebra the 

 neural arch is confined 

 to the anterior part of 

 its own centrum and the 

 ribs, which are short and 

 without costal plates, 

 meet those of the pre- 

 ceding vertebra. 



The skull (Figs. 227, 

 228) possesses only one 

 temporal arcade, the 

 lower, and the lateral 

 temporal fossa is there- 

 fore absent. In this 

 respect the skull is 

 mammal-like. The 

 roof consists of a sup- 

 raoccipital with a 

 strongly developed oc- 

 cipital crest, a pair 

 of parietals and a pair 

 of frontals. There 

 is no pineal foramen. 

 Descending lamellar processes of the parietals (Fig. 228, 1) reach 

 down to the pterygoids and take the place of the alisphenoids, 

 which are absent. Presphenoid and orbitosphenoids are also 

 absent. The epiotic is united to the supraoccipital ; the opis- 



FiG. 227. — A. Posterior, B. Anterior view of the skull of 

 Chelone midas (from Reynolds). 1 parietal, 2 squa- 

 mosal, .S quadrate, 4 basisphenoid, .5 basioccipital, 

 6' quadrato-jugal, 7 opisthotic, S exoccipital, .'' foramen 

 magnum, 1<> splenial, 11 articular, 12 dentary, i:i 

 angular, 14 supra-angular, IS premar.illa, l(! maxilla, 

 17 jugal, IS postfrontal, 19 vomer, 2t) prefrontal, 

 2/ frontal, 22 external auditory meatus leading unto 

 tympanic cavity. 



