Sauropsida: Class Reptilia 



467 



The general contour of the reptilian body is less streamlined 

 than that of typical aquatic anamniotes. A cervical region, at most only 

 faintly suggested in anamniotes, is distinctly differentiated in reptiles, 

 and in some, notably turtles, becomes much elongated. Gill-chambers, 

 with the intervening gill-arches and internal gills, require much space. 

 The absence of gills in the reptile permits of considerable narrowing of 

 the region just behind the head and, further, important functional 

 advantage is gained by the narrowing and elongating of the neck 

 region. A fish, to change the direction of the line of vision, must rotate 

 the whole body. It is of obvious advantage that the mobile neck of the 

 land animal enables it to "look around" without changing its position 

 and to look backward while running forward. Most modern reptiles 

 have relatively long tails. The very long tail of the chameleon is pre- 

 hensile and may be coiled around a twig to assist the lizard in holding 

 on to its perch in a tree. In some lizards, and in turtles and tortoises, 

 the tails are short. 



The paired appendages are somewhat more strongly developed 

 than in amphibians, although in living reptiles they are short and in 

 many cases incapable of lifting the body off the ground. Among extinct 

 reptiles, however, were some dinosaurs whose long and strongly built 

 legs indicate capacity for swift running. In the "ostrich dinosaurs" the 

 short forelegs and the long, powerful hindlegs suggest a habit of bipedal 

 locomotion (Fig. 360). In some reptiles legs are rudimentary or totally 



Fin. 360. Struthiomimus, an ostrich-like Cretaceous dinosaur, about 5 feet in height. 

 (Courtesy, \merican Museum of Natural History, New York.) 



