240 LEAVES FROM THE 



Take the cranium of a crocodile. A more solid, bony 

 mass, you could hardly see. Now turn to that of a boa. 

 The skull, you see, is made up of a considerable number 

 of pieces, all admirably fitted and joined together, but 

 with such an adaptation as easily to admit of separation. 

 Why is this ? The long head and widely extensive jaws 

 of the crocodile enable it to secure and take into the 

 stomach a comparatively large prey. But the serpent 

 frequently has to master and swallow an animal utterly 

 disproportion ed to the usual gape of the mouth ; the 

 skull is, therefore, so framed as easily to admit of partial 

 dislocation, so that it may aid the dilatation of the jaws 

 and throat, and facilitate deglutition. The ribs in the 

 frogs, as before observed, are almost null ; in the serpents 

 they are so lavishly developed, and so freely articulated, 

 that they are used as organs of motion. In the tortoises 

 they are implanted and incorporated with the rest of the 

 carapace. The ribs of a serpent may be compared to the 

 legs of a millipede situated internally, and operating ex- 

 ternally, principally by acting on the scutes of the belly 

 on which it creeps. Some reptiles have not only a true 

 breast-bone, but also an addition, which has been termed 

 an abdominal sternum. This may be seen in the croco- 

 diles, and seems to be produced by the ossification of the 

 tendons of the recti muscles. But while some have two 

 sterna, others have none at all. The chameleon, for 

 instance, though the ribs are well formed, has no breast- 

 bone. The tortoise, and the majority of saurians, are 

 gifted with four sufficiently well-developed extremities^ 

 Chirotes and bipes have only two; the former an 

 anterior pair, the latter a posterior pair, and those but 

 poorly framed. 



But though these and other great differences of orga- 

 nization are patent among the reptiles, every bone of 

 every reptile is marked with such peculiarity of character 

 as to indicate at once the class to which it belongs. A 



