CHAPTER XI 



SQUAMATA 



The order Squamata, so called because of the dermal covering 

 of overlapping horny scales, comprises the great majority of living 

 reptiles. Although the scaly covering is characteristic of nearly 

 all the members of the order, the most essential differences dis- 

 tinguishing them from other reptiles are, as usual, found in the 

 skeleton, and especially in the skull. The quadrate bone, that to 

 which the lower jaw is articulated on each side, is not wedged in 

 immovably between other bones of the skull, as in all other reptiles, 

 but is, instead, freely articulated with the cranium in such a way 

 that its lower end moves both backward and forward, as well as 

 inward and outward. This freedom of movement has in the past 

 been thought to be due to the loss of a lower temporal arch, a 

 bony bar connecting the lower end of the quadrate with the hind 

 end of the upper jaw, which is very characteristic, for instance, of 

 the Rhynchocephalia. Indeed, because of the many primitive 

 characters which the lizards possess, it has generally been supposed 

 that the order was an early branch of the rhynchocephalian stem. 

 But we are now quite sure that the lizards are as primitive as the 

 Rhynchocephalia, and that their origin, as an independent branch 

 of the reptilian stem, goes quite as far if not farther back — quite 

 sure that the ancestors of the lizards never had a lower temporal 

 arcade and two temporal vacuities, but that the looseness of the 

 quadrate bone has been due to the gradual loss of a bone which 

 covered the whole side of the skull until only the upper part of 

 it was left. In other words, the ancestral skull of the Squamata 

 must have been like that of Araeoscelis , more fully described under 

 the Protorosauria, a group than which there is perhaps none more 

 closely allied to the Squamata. 



The bones of the roof of the mouth of the Squamata — that is, 

 of the palate — are narrow and long, and are not closely articulated, 



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