VERTEBRATA: REPTILIA. 567 



form of the ischium, and the slenderness of the pubes. The 

 astragalus is like that of a bird, and in some cases appears 

 to have become anchylosed with the distal end of the tibia. 

 The metatarsal bones, however, remain distinct, and are not 

 anchylosed with any of the tarsal bones to form a "tarso- 

 metatarsus." 



The most familiar examples of the Dinosauria are Megalosaurus and 

 Iguanodon. 



Megalosaurus is a gigantic Oolitic Reptile, which occurs also in the 

 Cretaceous series (Weald Clay). Its length has been estimated at between 

 forty and fifty feet, the femur and tibia each measuring about three feet 

 in length. As the head of the femur is set on nearly at right angles with 

 the shaft, whilst all the long bones contain large medullary cavities, there 

 can be no doubt but that Megalosaurus \vas terrestrial in its habits. That 

 it was carnivorous and destructive in the highest degree is shown by the 

 powerful, pointed, and trenchant teeth. 



The Iguanodon is mainly, if not exclusively, Cretaceous, being especially 

 characteristic of the great delta-deposit of the Wealden. The length of 

 the Iguanodon has been estimated as being probably from fifty to sixty 

 feet ; and from the close resemblance of its teeth to those of the living 

 Iguanas, there is little doubt that it was herbivorous and not carnivorous. 

 The femur of a large Iguanodon measures from four to five feet in length, 

 with a circumference of twenty-two inches in its smallest part. From the 

 disproportionately small size of the fore-limbs, and from the occurrence of 

 pairs of gigantic three-toed footsteps in the same beds, it has been con- 

 cluded, with much probability, that Iguanodon^ in spite of its enormous 

 bulk, must have walked temporarily or permanently upon its hind-legs, 

 thus coming to present a most marked and striking affinity to the Birds. 



The most remarkable, however, of the Dinosauria, is the little Comp- 

 sognathiis longipes, from the Lithographic Slate of Solenhofen, referred to 

 this order by Professor Huxley. This Reptile is not remarkable for its 

 size, which does not seem to have been much more than two feet, but for 

 the singular affinities which it exhibits to the true Birds. The head of 

 Compsognathus was furnished with toothed jaws, and supported upon a long 

 and slender neck. The fore-limbs were very short, but the hind-limbs 

 were long and like those of Birds. The proximal portion of the tarsus 

 resembled that of Birds in being anchylosed to the lower end of the tibia ; 

 but the distal portion of the tarsus unlike that of Birds was free, and 

 was not anchylosed with the metatarsus. Huxley concludes that "it is 

 impossible to look at the conformation of this strange Reptile, and to 

 doubt that it hopped or walked in an erect or semi-erect position, after the 

 manner of a Bird, to which its long neck, slight head, and small anterior 

 limbs must have given it an extraordinary resemblance. " 



The researches of Professor Phillips, further, have now shown that the 

 gigantic Cetiosaurus of the Oolitic and Cretaceous rocks, formerly referred 

 to the Crocodilia, is truly a Deinosaur. Its total length is estimated at 

 probably not less than sixty or seventy feet. 



ORDER X. THERIODONTIA. This order has been founded 

 by Professor Owen for the reception of a number of carnivor- 

 ous Reptiles from deposits of Triassic or Permian age. The 

 Reptiles in question show some singular Mammalian affinities, 



