STRUCTURE OF OPHIDIANS. 



Fig. 16.* 



ately articulated with the cranium, as in Saurians and Chelonians, 

 but, in general, the tympanic bones are moveable. 



46. The true Serpents with immoveable tympanic bones also 

 have the upper jaw fixed to the cranium, and the mouth but little 

 dilatable, (l^ig. 16.): they form the small 



family of double walkers, Amphiibana, 



so called from their faculty of moving equally 



well, both forward and backwards. Those 



that form the genus of Amphisbaenji have 



the body surrounded by circular ranges of 



small quadrangular scales, like certain Scincoids ; the others. 



called TYPHLOPS, have small imbricate scales, and at first sight, 



resemble earth worms. These Ophidians inhabit the warmcoun 



tries of both continents: some of them are blind. 



47. True Serpents having moveable tympanic bones, form a 

 more numerous family Some of them resemble the preceding in 

 the cylindrical form of the head and body, and in the smallness of 

 their scales. The mouth is less dilatable than in other ophidians 

 of this division ; for the tympanic bone is directly articulated to 

 the cranium, while, in the last, it is suspended to a mastoid bone 

 which is itself moveable. The genus of Tortrix, possesses this 

 kind of organization. 



48. In all the ORDINARY SERPENTS, 

 we have yet to mention, the mouth 

 is so formed as to enable the ani- 

 mal to swallow bodies larger than 

 itself. The two branches of the 

 lower jaw are not united, and the 

 kind of peduncle which sustains 

 them ( the tympanic bone, Piy. 

 17, /.) is not only moveable itself, 

 but is suspended to another portion 



17.t 



* Explanation of Fig. 16. The bony head of an Ophidian of the division 

 of Amphisbaena. 



^Explanation of Fig. 17. Bony head of a Rattlesnake, c. the cranium, 

 ma. the mastoid bone which articulates by one extremity, with the 

 cranium, and bv the other, supports the tympanic bone, (.) mi. the lower 

 jaw suspended from the tympanic bone, n. the vomer and nasal bones, m. 

 the moveable upper jaw bone, pi. one of the plerygoid bones (portions of 

 the sphenoid,) the internal of which is continuous with the palatine arches, 

 p, pe. palatine teeth. d. the poisonous fangs. 



46. What are Amphisbaenae ? . 



47. What is the organization of the head in the genus Tortrix ? 



48. What peculiarities in the structure of the head enable certain Sernenls 

 to swallow bodies larger than themselves? 



2L 



