EMYDOSAURI. 55 



jaw. They are internally hollow, and of the same number 

 in all the ages of the animal, the increasing size of the jaw 

 being provided agamst by their constant reproduction. They 

 are reproduced by a new tooth growing from the base of 

 the alveola and causing the absorption of the root of the 

 older one. The tongue is short, fleshy, flat, and attached 

 near its edge. The lower jaw is prolonged beyond the skull, 

 so that the upper jaw appears to be moveable. Their nostrils 

 are small, crescent-shaped, and placed at the end of the 

 muzzle ; they are closed by a small valve. The eyes are fur- 

 nished with three eyelids, and the ears are closed with two 

 fleshy valves ; under the throat there are two small seba- 

 ceous glands emitting a musky odour, (see Bell, Phil. Trans. 

 1829.) 



The neck is short, and covered with smaller scales. There 

 is generally a row of small isolated shields placed immediately 

 behind the occiput, called the Nuchal plates (Scuta nuchce), 

 and a shield of close set plates behind these, called the Cer- 

 vical plates {Scuta cervicis). The body is depressed ; the tail 

 compressed ; and the sides, back, and tail covered with longi- 

 tudinal rows of square bony shields, which are generally 

 keeled and form high crests, especially on the top of the tail 

 where they form two crests at the base united into one at 

 the tip. The sides are nakedish or covered with small 

 scales and capable of great dilatation. The belly and under 

 side of the tail are covered with smooth thin square scales. 

 The vent is a longitudinal slit ; the penis of the male is single 

 and perforated, and the vagina of the female is equally simple. 



The fore-legs are short, the feet are more or less webbed, 

 the anterior with four, and the hinder with five toes, of which 

 only the three interior on each foot are clawed. 



The heart is three-celled and the lungs are not sunk into 

 the abdomen as in other reptiles. 



The vertebrae of the neck are furnished with projecting 

 lateral false ribs, which touch at their extremities, and do not 

 allow the animal to turn its neck from side to side. Their 

 sternum is prolonged beyond the ribs and supports a kind of 

 false ribs which are not jointed to the vertebree, but serve to 

 protect the abdominal viscera ; they have no clavicle. 



These animals inhabit fresh-water rivers in tropical cli- 

 mates, living on animals, which they kill by drowning, and 

 then leave under water till partly putrid before they feed on 

 them. 



