344 ZOOLOGY SECT. 



maxillae, the maxillae and the palatines ; and some resembled the 

 living members of the order in having such plates developed also 

 from the pterygoids ; all had the external nares situated towards 

 the end of the snout. Those in which the palatine plates of the 

 pterygoids were absent had usually amphicoelous vertebrae. Some of 

 the fossil Crocodiles reached an immense size. 



4. EXTINCT GROUPS OF REPTILES. 



THEROMORPHA. 



THE Theromorpha are a group of fossil Reptiles which exhibit remarkable 

 points of resemblance to the Amphibia (Stegocephala), on the one hand, and to 

 the lower Mammals on the other. They were lizard-like in shape, with limbs 

 adapted for terrestrial locomotion. When the vertebral centra are complete, 

 they are amphicrelous. A sternum is present, and also an episternum. There 

 is a sacrum composed of from 2-6 vertebra?. Abdominal ribs are absent in 

 most. The quadrate is firmly united with the other bones of the skull. The 



FIG. 952. Left lateral aspect of the skull of Galesaurus planiceps Or. orbit. (After 



Nicholson and Lydekker.) 



pre-maxilla is single ; in some the maxilla? develop palatine plates. There is a 

 parietal foramen, and sometimes one temporal arch is developed, sometimes two. 

 The pterygoids meet in front of the basi-sphenoid, diverging anteriorly where the 

 small palatines lie between them. In the pectoral arch there are clavicle, 

 coracoid, pro-coracoid, and scapula, the last having a process the acromion 

 process with which the pro-coracoid articulates. The pubes and ischia are 

 closely united, and an obturator foramen is absent or extremely small. The 

 teeth (Fig. 952) (which are not present in all) are thecodont, and in the higher 

 forms bear a considerable resemblance to those of mammals in the regularity of 

 their arrangement in sets, often with large canines or tusks. Palatine teeth are 

 sometimes present. The Placodontia have remarkable broad crushing teeth on 

 "both upper and lower jaws and on the palate. 



The Theromorpha only occur in beds of Permian and Triassic age, and have 

 been found in South Africa and North America as well as Europe. 



SAUROPTERYGIA. 



The typical representatives of this order, such as the Plesiosaurs (Fig. 9.53), 

 were aquatic Reptiles, sometimes of large size (up to 40 feet), though many were 

 quite small. They had a lizard-like body, a very long neck, supporting a 

 relatively small head, and a very short tail ; the limbs were modified to form 

 swimming-paddles. In older and less specialised members of the group, how- 

 ever, the limbs were not paddle-like, but adapted for walking. 



The spinal column of the Sauropterygia is characterised by the great length 



