XIII 



PHYLUM CHORDATA 375 



and lower parts by a bar formed from the post-frontal and squamosal. Ecto- 

 pterygoids are present. The quadrate is firmly fixed. In the pectoral arch the 

 scapula is very large, the coracoid small, and the pro-coracoid and clavicle 

 absent. The pubis in some Dinosauria has a remarkable slender prolongation 

 (Fig. 1016, 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 resemblance to Birds. 

 The teeth, which are usually compressed and may have serrated edges, are 

 sometimes placed in sockets, sometimes in grooves. 



Iguanodon (Fig. 1016), 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 ; 



FIG. 1017. Teeth uf Iguanodon mantelli. A, from the inner, D, from thu outer side. 

 (From Zittcl, after Mantell.) 



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. 1017) 

 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. 



PTEROSAURIA. 



The Pterosauiia or Pterodactyles are perhaps even more remarkable modifica- 

 tions 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 associated 

 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. 1018) the last digit on the 

 ulnar side of the manus is enormously prolonged and thickened, and supported a 

 web of skin (Fig. 1020) which extended backwards to the hind-limbs and the 

 tail. Most of the bones are hollow, and have pneumatic foramina as in Birds 



A A 2 



