FOSSIL REPTILES. 259 



sea>tortoise. The palatines do not unite below to prolong the 

 palate ; they are hollowed into a demi -canal in front, and less 

 extended than in the land-tortoises. The body of the sphenoid 

 reaches to them, proceeding between the two pterygoidean 

 bones, which are not united one to the other, but go from the 

 lateral occipital, between the tympanic cavities and the basilary 

 bone, and at the sides of the body of the sphenoid, as far as the 

 palatines and maxillaries, which renders all the basilary and 

 palatine region broad and flat. 



The anterior frontals advance between the maxillaries, and 

 in this part occupy exactly the place of the proper nasal bones, 

 without being distinguished by any suture. They even form a 

 point over the external aperture of the nostrils, as the bones of 

 the nose often do in the mammifera. 



The principal frontals form almost a square. They reach the 

 edge of the orbit. The posterior frontal is as wide above as it 

 is high. The jugal forms a part of the posterior and lower 

 edge of the orbit, and almost all the zygomatic arch, of which 

 the squamous temporal bone constitutes but a small portion in 

 front of the tympanic cavity. This last has its frame complete. 

 The osselet passes through a foramen into the second chamber, 

 which, as in the other tortoises, is closed behind only by carti- 

 lage. 



The spine of the occiput and the mastoidean tuberosities 

 are all pointed, and more salient behind than the articulary 

 condyle. The space occupied by the os tympani at the poste- 

 rior edge of the temporal foss is very narrow, but it widens in 

 re-descending towards its apophysis for the lower jaw. The 

 temporal wing is placed below and in front of the grand fora- 

 men of the fifth pair, and the descending portion of the parietal 

 articulates in front of it to the internal pterygoid bone. There 

 is no trace of an anterior sphenoid, or of its wings. Its place 

 is held by a slender membrane, which closes on each side the 

 forepart of the cerebral cavity. 



The principal character of the Marine Tortoises, or Chelo- 



S 2 



