CHELONIA. 473 



their place ; neither presphenoid nor orbitosphenoids are ossified ; there 

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

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

 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, 

 anterior 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. 



Some Peculiarities in the Organs of Chelonia. 



The brain of the adult shows a slight curvature. In Chelonians and 

 in all higher animals except serpents, there are twelve cranial nerves, 

 for in addition to the usual ten, a hypoglossal to the tongue, and a 

 spinal accessory to cervical muscles are ranked as the eleventh and 

 twelfth. 



The gullet often bears internally pointed horny papillae directed down- 

 wards. There are blind pockets or anal bursae connected with the 

 cloaca. 



The heart is three-chambered, but an incomplete septum divides the 

 ventricle into a right portion from which the pulmonary arteries and the 

 left aortic arch arise, and a left portion from which the right aortic arch 

 issues. From the right aortic arch, which contains more pure blood 

 than the left, the carotid and subclavian arteries are given off. The 

 left aortic arch gives off the coeliac artery before it unites with the right. 



Unlike other Reptiles, the Chelonians are said to have no renal portal 

 system. 



The lungs are attached to the dorsal wall of the thorax, and have only 

 a ventral investment of peritoneum ; each is divided into a series of 

 compartments into which branches of the bronchus open. There is a 

 slight muscular diaphragm. 



In the males, the kidney, the epididymis, and the testis, lie adjacent 

 to one another on each side. The males have a grooved penis attached 

 to the anterior wall of the cloaca. There is a urinary bladder. 



Classification of Chelonia. 



Order I. Athecata. 



SphargidiE, leather-turtles, with flexible carapace. Sphargis coriaceus, 

 the only living species, the largest modern Chelonian, sometimes 



