CROCODILIA. 



97 



opposite side of the arch. The smooth expanded horizontal plate which efifects the 

 latter junction, shown in PI. 1 B, and PI. A % at 21, is called the palatal plate of the 

 maxillary ; the thickened external border, where this plate meets the external rough 

 surface of the bone, and which is perforated for the lodgement of the teeth, is the 

 ' alveolar border' or ' process' of the maxillary. The haemal spine or key-bone of the 

 arch (22) is bifid, and the arch is completed by the symphysial junction of the two 

 symmetrical halves at H iv, fig. 13 ; these halves are called ' premaxillary bones ;' 



Ym. 13. 



Disarticulated bones of tlie Skull of an Alligator, N i to iv tlie neui-al arches ; H I to iv the hajmal arches 



and appendages. 



these bones, like the maxillaries, have a rough facial plate, PI. 1 A, 22 and a smooth 

 palatal plate PI. 1 B, 22, with the connecting alveolar border. The median symphysis 

 is perforated vertically through both plates ; the outer or upper hole being the external 

 nostril, the under or palatal one being the prepalatal or naso-palatal aperture ; this is 

 completely inclosed by the premaxillary bone, as shown in PI. 1 B, fig. 2, 22, and 

 PI. 1 C, 22, np ; whilst, in all known existing Crocodiles and Alligators, the tips of tlic 

 nasal bones, as at 15, fig. 1, PI- A 2, enter into the back part of the circumference of 

 the nasal aperture. In the Gavials, as may be seen in PI. 1, fig. 1 a, the nasal aperture 

 is wholly surrounded by the premaxillaries, i ; and one of the fossil Eocene Crocodiles, 



