FOSSIL REPTILES. 257 



applicable to all land tortoises. In the testudo Grcsca the 

 cranium is less gibbous between the orbits. The principal 

 frontals, more long than broad, reach to the edge of the orbit, 

 between the two frontals, and re-descend into its roof. 



In the emydes, or common fresh-water tortoises, the head is 

 more flatted. The principal frontals, though more broad than 

 long, do not always reach the edge of the orbit, as, for example, 

 in the testudo Europcea. The posterior frontal is broader. The 

 frame of the tympanum is not complete ; and instead of a fora- 

 men, there is a scissure for the passage of the auditory osselet, 

 from one chamber of the cavity into the other. The basilary 

 region and the palatine make but one plan, the palatines not 

 even being concave. The test, scripta, picta, scabra, dorsata, 

 centrata^ dausa, virgulata, are all thus distinguished. 



Some emydes, as the emys expansa, have characters in com- 

 mon with the sea and fresh-water tortoises, and others beside, 

 peculiar to themselves. The head is depressed, the muzzle 

 short, the orbits small and very forward. There is no osseous 

 vomer, so that the two back-nostrils form but one foramen in 

 the skeleton. The palatines have not the palatine portion. 

 The frame of the first chamber of the tympanic cavity is com- 

 plete. This chamber communicates only by a narrow foramen 

 with the masto'idean cellule, and the Eustachian tube origi- 

 nates there by a cleft which is an extension of the foramen 

 through which the osselet passes into the second chamber. 



The temple is covered as in the sea-tortoises by the parietal, 

 the temporal, the jugal and the posterior frontal bones. The 

 last of these is very narrow. It has a portion descending into 

 the temple, which, uniting itself to an ascending portion of the 

 palatine, and a re-entering portion of the jugal, forms a parti- 

 tion, which separates the orbit from the temporal fossa, leaving 

 no communication but a large foramen near this descending 

 part of the parietal, which replaces the temporal wing. 



The pterygoid bone unites itself in front to the palatine and 

 jugal, and not to the maxillary, which does not extend so far 



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