364 



ZOOLOGY 



SECT. 



The pubis in some Dinosauria has a remarkable slender prolongation (Fig. 

 1027, pp.) running downwards and backwards from the body of the bone 

 parallel with the ischium, an arrangement not found elsewhere except in 

 Birds ; a pubic symphysis does not always occur. In certain points in the 

 structure of the hind-limb itself some of the Dinosauria also bear a resem- 

 blance to Birds. The teeth, which are usually compressed and may have 

 serrated edges, are sometimes placed in sockets, sometimes in grooves. 



Iguanodon (Fig. 1027), one of the best-known genera, attains the length 

 in the case of one species of over 30 feet. The limb-bones are hollow. The 

 ischium and pubic process are long and slender, and inclined backwards and 

 downwards parallel to one another. The hind-foot was digitigrade, i.e., the 

 weight was supported on the phalanges of the digits, and the elongated meta- 

 tarsals, which were immovably fixed, had a nearly vertical position as in 

 Birds ; the fore-limbs are relatively small, and fossil footprints that have 

 been found indicate that the animal supported itself habitually in a half- 

 erect posture like a Kangaroo, with the fore-limbs raised from the ground. 

 The teeth (Fig. 1028) are of a remarkable shape, flattened and with serrated 

 edges, sometimes with vertical ridges which may be serrated. The Dinosauria 

 range from the Trias to the Upper Cretaceous, and were most abundant in 

 the Jurassic and Wealden. 



PTEROSAXTRIA. 



The Pterosauria or Pterodactyles are perhaps even more remarkable 

 modifications of the reptilian type than any of the orders that have been 



hitherto alluded to. The chief 

 peculiarities in the structure 

 of these Reptiles were asso- 

 ciated with a flying mode of 

 locomotion, the organs of 

 . flight being, as in the Bird 

 and the Bat, the fore-limbs. 

 In the Pterodactyles (Fig. 

 1029) the last digit on the 

 ulnar side of the manus is 

 enormously prolonged and 

 thickened, and supported a 

 web of skin (Fig. 1031) which 

 extended backwards to the 

 hind-limbs and the tail. Most 

 of the bones are hollow, and 

 have pneumatic foramina as 

 in Birds (q.v.). The vertebrae 

 are precocious, except the 

 caudals, which are amphi- 

 ccelous. The cervical verte- 

 brae are elongated and stout, 

 the neck being of considerable 

 length ; there are three to six 

 ankylosed sacrals. The an- 

 terior thoracic ribs are bifid 

 at their vertebral ends. The 

 sternum is broad, with a 

 longitudinal keel. The skull 

 (Fig. 1030), set on the neck at right angles as in a Bird, is of large size and 

 superficially resembles that of a Bird in general shape, 'and particularly in 

 the presence of an elongated, pointed rostrum ; the orbits are large, and 

 contain a ring of sclerotic ossifications. The sutures are largely obliterated, 



FIG. 1029. Pterodactylus spectabilis. Three- 

 fourths of the natural size. (From Zittel, after 

 H. v. Mayer.) 



