X ORTHOPODA ORNITHOPODA 427 



the Upper Jurassic and the Wealden of North America and 

 England. Five fingers, with 2, 3, 3, 3, 2 phalanges and four 

 toes, with 2, 3, 4, 5 phalanges, but the hallux is much shortened 

 and does not touch the hard ground ; astragalus and calcaneum 

 separate. 



Laosaurus of Colorado is a smaller form, intermediate in 

 structure between the former genus and Hypsilophodon foxi from 

 the Wealden of the Isle of Wight. A small creature, less than 

 5 feet in length. Four fingers, with 2, 3, 4, 2 phalanges ; 

 fifth metacarpal vestigial. Four toes with 2, 3, 4, 5 phalanges 

 and long claws. Astragalus and calcaneum separate. Post-pubis 

 very slender. Each premaxillary with five pointed alveolar 

 teeth, leaving a wide median diastema ; maxillaries with eleven, 

 dentaries with ten laterally compressed blade-like teeth. 



Iguanodon from the Wealden of England, Belgium, and 

 Germany. Apparently two species, /. mantelli, about 16 feet, 

 /. bernissartensis nearly 30 feet long. The premaxilla is 

 quite toothless ; the teeth of the maxillae and mandibles stand 

 in close series, implanted in alveolae ; they are spatulate, laterally 

 compressed, with finely serrated edges, and slightly curved, the 

 lower outwards, the upper inwards, and bear a general resemblance 

 to those of Iguana, hence the generic name. There is only one 

 functional set of teeth, and these are much worn down by use, 

 but in such a way that, owing to the different curvature of 

 the opposed teeth, the worn-down crowns form cutting, and at 

 the same time crushing, almost triturating surfaces, indicating 

 that these animals lived upon herbs. The gait of these 

 creatures was upright, as shown by their spoors ; the long 

 almost vertical ischia, which form a padded symphysis, only 

 slightly raised above the ground, suggest that this symphysis was 

 used as a true sitting support, the animal resting upon it, the 

 hind-limbs and the long tail. The latter, to judge from the long 

 chevrons and the high neural spinous processes, must have been 

 furnished with strong muscles. The whole tail was undoubtedly 

 used as a balance during the upright position. Many of the 

 tendons of the dorsal spinal muscles on the back and upper half 

 of the tail are ossified. The post-pubic branches are very slender, 

 distally much reduced, and, except at the obturator -foramen, 

 separated from the ischia ; the pre-pubes are very strong and 

 broad. The femur has a fourth trochanter, a feature which 



