346 



ZOOLOGY 



SECT. 



ICHTHYOPTERYGIA. 



The Ichthyopterygia, including Ichthyosaurus (Fig. 956) 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, and with the limbs in the form of swim- 

 ming-paddles. The vertebrae are amphiccelous. A 

 sacrum is absent, so that only pre-caudal and caudal 

 regions are distinguishable. The ribs have two 

 heads for articulation with the vertebra? : 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 pre-maxilla?, 

 and with small nostrils situated far back. The 

 orbits are large and contain a ring of bones developed 

 in the sclerotic. A columella is present as in Lizards, 

 and there is a large parietal foramen. Both tem- 

 poral arches are developed. The quadrate is im- 

 movably fixed to the skull. The pterygoids meet 

 in the middle line and extend forwards to the 

 vomers, so as to separate the palatines, as in Hat- 

 teria. The pectoral arch contains only coracoid, 

 scapula and clavicle, the pro-coracoid being absent. 

 The coracoids are broad bones which meet vent rally 

 for a short distance without overlapping. 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 dis- 

 tribution, having been found not only in Europe and 

 North America, but in the Arctic Regions, in India, 

 Africa, Australia, and New Zealand. 



o 



fe 



o 







s 



o 

 o 



!/! 



I 



(A 

 O 



ft 

 O 



H 



DlNOSAURIA. 



This order comprises a vast number of terrestrial 

 Reptiles, some of gigantic size, of lizard-like or bird- 

 like fonn, some approaching Birds in certain features 

 of their structure, others coming nearer the earliest 

 fossil Crocodiles. The surface was in some covered 

 with a bony armour, sometimes armed with long 

 spines. The fore- and hind-limbs were in some 

 rqually developed ; in others the hind-limbs were 



much more powerful than the fore, and in many their structure appears 



adapted to a bipedal mode of progression (Fig. 957). 



The centra are in general amphicoelous. The sacral region usually comprises 



3 to 6 vertebra-. The thoracic ribs have double heads. Abdominal ribs are 



sometimes present. The sternum was incompletely ossified. The pre-maxilhe 



