228 EEPTILIA. 



palatine plates of which the posterior nares open. The pterygoids 

 are very broad and lamellar. Teeth are completely absent, both on 

 the palatal bones and on the high, relatively short bones of the jaws, 

 but the edges of the latter are covered, like the beak of a bird, by 

 sharp cutting, serrated horny plates, which enable certain species 

 to bite with great vigour and to inflict sensible wounds. 



The four limbs enable the Ghelonia to creep and run on land : in 

 the aquatic forms, however, they are swimming feet or fins. The 

 position of the pectoral and pelvic girdles, and of the corresponding 

 muscles, between the dorsal and ventral shields, is remarkable ; but is 

 fully explained developmentally by the growth of the anterior and 

 posterior ribs. The scapula is formed of an ascending rod-like bone, 

 the upper end of which is attached to the transverse process of the 

 anterior thoracic vertebra by a ligamentous or cartilaginous connec- 

 tion. A strong acromial process (procoracoid) reaches from the 

 scapula to the unpaired portion of the ventral shield, to which it is 

 likewise attached by a ligamentous or cartilaginous connection. The 

 pelvis closely resembles that of the Saurians, and except in the Land 

 Tortoises is not firmly connected with the carapace. 



In the organs of digestion and reproduction Chelonians partly 

 resemble Crocodiles and partly Birds. They especially resemble the 

 former in the structure of the male generative organs, and in the 

 possession of peritoneal canals, which are, however, closed. The 

 opening of the genital ducts and the ureters into the neck of the 

 urinary bladder, which accordingly functions as a urogenital sinus, 

 is worthy of remark. The eyes are placed in closed orbits, and have 

 Jids and a nicticating membrane. There is always a tympanic 

 cavity with a wide Eustachian tube, a long columella and a tym- 

 panic membrane, which is visible externally. The tongue is attached 

 to the floor of the buccal cavity, and is not protrusible ; in the Land 

 Tortoises it is beset with long papillae. 



The copulation lasts a day, and during that time the male is 

 carried on the back of the female. The eggs are laid in small 

 number, except in the marine Chelonia, in which they are more 

 numerous. They contain within the shell a layer of albumen, sur- 

 rounding the yolk, and are buried in the earth, in the aquatic 

 Chelonians near the shore. According to Agassiz the North American 

 Marsh Tortoises lay eggs only once in the year, while they copulate 

 twice (in the spring and autumn). The first copulation, according 

 to this investigator, takes place in Emys picta in the seventh year, 

 the first deposition of eggs in the eleventh year of the animal's life. 



