THE CROCODILIA. 255 



bones ; supra-temporal, lateral-temporal, and post-temporal 

 fossas are formed, as in the Lacertilia, though their relative 

 sizes are very different. 



4. The maxillary and the palatine bones develope palatine 

 plates, which unite suturally in the middle line, and sepa- 

 rate the nasal passages from the cavity of the movith, as in 

 Mammalia; and in all existing Crocodiles, but not in Teleo- 

 saurus or Belodon, the pterygoids are also modified in the 

 same way (as in Mymercophaga among Mammals), so that 

 the posterior nares are situated very far back beneath the 

 base of the skull. 



5. In consequence of the development of these palatine 

 plates of the maxillary and palatine bones, the two vomers 

 are, in most Crocodiles, invisible upon the under- surface 

 of the bony roof of the mouth. 



6. There are large aiisphenoids, but the orbitosphenoids 

 are alssent or rudimentary. 



7. There is no parietal foramen. 



8. The quadrate bone is very large, and fixed immoveably 

 to the walls of the skull, as in the Chelonia ; and, as in the 

 latter, the pterygoid bone is firmly connected with the base 

 of the skull, and united only with the upper and inner sur- 

 face of the quadrate bone. 



9. The pterygoid sends down a large free process, against 

 the broad outer edge of which the inner surface of the 

 mandible plays. 



10. The tympanic cavity is completely bounded by bone. 

 The pro-otic and opisthotic (which is united with the 

 ex-occipital) form its inner walls, the quadrate its outer 

 wall, the squamosal and postfrontal its roof, and the quad- 

 rate, the basi-occipital, and basisphenoid its floor. The 

 two tympana are placed in communication with the cavity 

 of the month by three canals— one large, opening in the 

 middle line ; and two smaller ones at the sides, on the base 

 of the skull, behind the posterior nares. The large canal 

 passes up between the basisphenoid and basi-occipital, and 

 divides between those bones into a right and left lateral 

 canal. Each lateral canal subdivides into an anterior 



