362 



ZOOLOGY 



SECT. 



ICHTHYOPTERYGIA. 



The Ichthyopterygia, including Ichthyosaurus (Fig. 1026) and its allies, 

 were aquatic Reptiles, some of very large size (30 or 40 feet in length), with 

 somewhat fish-like body, large head produced into an elongated snout, no 

 neck, and an elongated tail, with a large vertical 

 caudal fin, and with limbs in the form of swimming- 

 paddles. The vertebrse are amphiccelous. A 

 sacrum is absent, so that only precaudal and caudal 

 regions are distinguishable. The ribs have two heads 

 for articulation with the vertebrse : a sternum is 

 absent, but there is a highly developed system of 

 abdominal ribs. The skull is produced into an 

 elongated rostrum, formed chiefly of the premaxillse, 

 and with small nostrils situated far back. The 

 orbits are large and contain a ring of bones developed 

 in the sclerotic. An epipterygoid is present as in 

 Lizards, and there is a large parietal foramen. 

 Both superior and inferior temporal arches are 

 developed. The quadrate is immovably fixed to the 



Pb. 



FIG. 1025. Plesiosaurus, pelvic arch. 11. ilium ; Is. 

 ischium ; Pb. pubis. (After Huxley.) 



skull. The pectoral arch consists of coracoid, scapula, 

 and clavicle, the pro-coracoid being absent or very 

 small. The coracoids are broad bones which meet 

 ventrally for a short distance without overlapping. 

 A T-shaped episternum is present. The bones of the 

 pelvis are not strongly developed ; the ilia are 

 not connected with the spinal column ; the pubes 

 and ischia of opposite sides meet in ventral symphyses, 

 but there is no obturator foramen. Humerus and 

 femur are both short, and the rest of the bones of 

 the limb are disc-like or polyhedral. The phalanges 

 are numerous, and are usually in more, sometimes in 

 fewer, than the usual five series. The teeth are not 

 in separate sockets, but set in a continuous groove. 

 The Ichthyopterygia are of Mesozoic age, ranging 

 from the Upper Trias to the Upper Cretaceous. 

 Geographically their remains have a very wide distribution, having been 

 found not only in Europe and North America, but in the Arctic Regions, in 

 India, Africa, Australia, and New Zealand. 



DINOSAURIA. 



This order comprises a vast number of terrestrial Reptiles, some of gigantic 

 size (up to over 100 feet in length), of lizard-like or bird-like form, some 



