372 



ZOOLOGY 



considerable resemblance to those of Mammals in tlie regularity of their 

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

 sometimes present. One order, the Placodontia, have remarkable broad crushing 

 teeth on both upper and lower jaws and on the palate. 



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

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



Among them have recently been found 



1 many transition forms which tend to 

 ■^ bridge over the interval between the 



2 Reptilia and the Mammalia. 

 'S 



^ Sadkoptbbyoia. 



J The typical representatives of this 



3 order, such as Plesiosaurus (Fig. 1012), 

 a were aquatic Reptiles, sometimes of 

 S large size (up to 40 feet), though many 







a 



A 

 Pi 



Flu. 1013.— Plesiosaurus, poctoral arch, cm: 

 coracoid ; e. epistenium ; gi, glenoid cavity ; 

 ac. scapula. (After Zittel.) 



3 were quite small. They had a lizard- 



" like body, a very long neck, sup- 



porting a relatively small head, and a 



3 short tail which supported a vertical 



■I caudal fin ; the limbs were modified to 



J form swimming-paddles. In older and 



S less specialised members of the groxip, 



'f however, the limbs were not paddle-like, 



2 but adapted for walking. 



3 The spinal column of the Sauro- 

 £ pterygia is characterised by the great 

 "^ length of the cervical, and the shortness 



of the caudal region. The vertebra; are 

 usually amphica'lous. The sacrum consists of either one or two vertebrte. There 

 is no sternum. In tlie skull there are large premaxillEe ; a bony palate is 

 absent ; a transverse bone is present. One temporal arch only is developed. 

 There is a well-marked parietal foramen. The ring of bony plates (developed m 

 the sclerotic) found in the orbit of some fossil Reptiles is not developed. The 

 quadrate is not movable. The pectoral arch (Fig. 1U13) presents some remark- 



