146 OPHIDIA. 



another purpose in the animal's economy. The 

 ribs are immensely numerous and encircle a great 

 part of the trunk; and the free extremities of 

 these form, as we shall presently describe, the 

 ordinary instruments of progressive motion in 

 this Order. The vertehrce, or joints of the spine, 

 are connected not by two hollow facets, fiDed 

 up with cartilage, but by one convex face, filling 

 that which is concave. 



With a few exceptions, which form the con- 

 necting links with the Saurians, and are but a 

 step removed in structure from the species last 

 noticed, the Serpents are characterised by a 

 remarkable looseness of the bones of the skull, 

 and in particular by the mode in which the jaws 

 are articulated. These reptiles are ordained to 

 prey upon animals whose size much exceeds that 

 of any part of their own bodies, or heads, and 

 yet they are not furnished with any apparatus 

 either of teeth or claws, by which their food may 

 be divided ; it must be swallowed whole. The 

 elasticity of membranous viscera, such as the 

 gullet or the stomach, we readily conceive, might 

 be sufficiently great to allow of the passage of 

 large masses of food ; but the fixed and unyield- 

 ing nature of the bones of the mouth in most 

 animals would prevent the possibility of this. In 

 the reptiles before us, however, a singular and 

 beautiful deviation from this ordinary condition 

 of fixity in the bones of the mouth meets the 

 necessity of the case, and allows of an immense 

 expansion of the parts. The structure may be 

 thus familiarly explained. The lower jaw, which 

 is much longer, and extends much farther back 

 than the skull, is not hinged to the upper jaw, 



