690 



EEPTILIA. 



Fig. 339. 



and the nasal passages leading from them are prolonged through the 

 whole length of the upper jaw until they communicate with the fauces, 

 behind the velum of the palate (g}. Such being the arrangement, it is 

 immediately obvious that, when the communication between the mouth 

 and the fauces is cut off by means of the two valves (</,/), the Crocodile, 

 by merely keeping the tip of its snout above the water, breathes with 

 the utmost facility, and it is thus enabled to keep its prey submerged 

 for any length of time that may be requisite to extinguish life. 



(1926.) The teeth of the Crocodile and of the higher Saurians are 

 not merely consolidated with the bones of the skull to which they are 

 appended, but are implanted in sockets formed in the bones composing 

 the upper and lower jaws. Each tooth is a simple hollow cone, and 

 encloses a vascular 

 pulp, from the surface 

 of which the bony 

 matter of the tooth 

 was formed. When 

 a tooth becomes old 

 and worn, a second is 

 secreted by the same 

 pulp within the cavity 

 of the first, and the 

 original one is shed, 

 so that a succession 

 of teeth thus make 

 their appearance. 



(1927.) The ali- 

 mentary canal of Hep- 

 tiles offers little that 

 requires special de- 

 scription. The oeso- 

 phagus (fig. 343, //) 

 is generally extremely 

 capacious, and the 

 stomach of very variable shape and capacity. The latter viscus is for 

 the most part pyriform, tapering gradually towards the pylorus ; such 

 is the case in the CHELONIA and in the BATRACHOID AMPHIBIA : in 

 SERPENTS it resembles a long bowel, and is capable of extraordinary 

 dilatation ; and in the PERENNIBRANCHIATE AMPHIBIA, as in the Proteus 

 (fig. 340, i) and the Menopoma (fig. 343, g\ it looks like a mere dilata- 

 tion of the intestine. 



(1928.) The stomach of the Crocodile is remarkable as affording an- 

 other among the innumerable instances that might be adduced of that 

 gradual transition everywhere observable as we pass from one class of 

 animals to that which next succeeds it in the series of creation. The 



Stomach of the Crocodile. 



