324 LEAVES FROM THE 



be the result of an ossification of the tendinous portion 

 of the recti muscles. True clavicles there are none, but, 

 as in the rest of the Saurian tribe, the coracoid apophyses 

 are attached to the breast-bone. The lungs of reptiles 

 generally reach down into the abdomen ; but such is not 

 the case with the crocodilians, and some fleshy fibres 

 adhering to that part of the peritoneum which covers the 

 liver, remind the observer of a diaphragm. This organi- 

 zation, combined with their trilocular heart, where the 

 blood coming from the lungs is not mingled with the 

 venous portion of that fluid, which comes from the body, 

 so completely as it is in other reptiles, appi'oximates, 

 though in no great degree, the crocodilians to the warm- 

 blooded quadrupeds. As in the tortoises, the auditory 

 bone and the pterygoid apophyses are fixed to the skull. 

 But the jaws, which in the chelonians are edentulous, 

 are furnished with numerous large conical teeth of une- 

 qual length, implanted in a single row in the thickness 

 of the upper and lower maxillary bones, in separate 

 cavities, each of which may be looked upon as a true 

 alveolus or socket. This formidable array is constantly 

 kept up in good order and condition by a provision which 

 insures a constant supply of serviceable teeth. Each 

 tooth is hollowed at the base, so as to become the case 

 or sheath of the tooth, of greater size, destined to replace 

 it ; so that, in the crocodiles, the operation of teething 

 is always painlessly going on : nor does the number of 

 the teeth vary according to age. The pressure of the 

 rising tooth causes an absorption of the hollow base of 

 the old one ; and as the former advances the latter 

 dwindles, till it drops out and is succeeded by the new 

 one. It need hardly be observed, that great solidity and 

 strength result from this double gomphosis ; while, to 

 add to the firmness of the terrible apparatus, the sockets 

 are directed obliquely from front to rear. Each tooth is, 

 so to speak, insulated ; and a gum, or at least what does 



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