LIFE IN SECONDARY TIMES 259 



bad the aspect of a Frog as large as an Ox, and had a short 

 tail. These Reptiles attained a length of two and half metres. 

 Their membranous skull was entirely covered with bony 

 dermal plates, leaving a hole for the parietal eye. These plates 

 were rugose as if they had been hewn, and in Elginia, a related 

 form, had peculiar spiny processes. The teeth were small and 

 uniform, with several serrated points, arranged in series, and 

 arose from both jaws and the palate. The limbs, short and 

 squat, each terminated in five digits, whereas the Stegocephala 

 never have more than four. The skull articulated with the 

 vertebral column by a single condyle, as in the case of the 

 Reptiles, whereas Batrachians have two. The lower jaw, 

 made up of several parts, was attached to the skull by 

 a quadrate bone united to it. The shoulder girdle com- 

 prised a scapula, a united coracoid and precoracoid, and a 

 cleithrnm. These characters are clearly Reptilian, but in the 

 shoulder we already observe some features which appear later 

 in Mammals. The coracoid bones are united with the 

 scapula in the manner of the coracoid process of the Mammals 

 and the scapula is provided with a spine characteristic of these 

 animals. These characters are accentuated in the pelvic girdle, 

 constructed on exactly the same plan as in Mammals, and 

 which articulates with two or three vertebrae constituting a 

 sacrum. Pareiasaurus and Elginia form the first group of 

 Theromorpha, the Pareiasaurians. 



In a second group, the Theriodonta or animals with 

 mammalian teeth, the bony envelope of the skull remains in- 

 complete as among the other Theromorpha. In these animals 

 however, some very remarkable modifications are produced 

 in the dentition. The teeth no longer serve merely to hold the 

 prey ; they also grind the food — the Reptile uses them, as later 

 on the Mammals used theirs ; nor is the number very different. 

 We can already classify them as incisors, canines, and molars. 

 The dental formula of Lycosaurus, for example (i| c} m£), 

 might be applied to the mammalian Marsupials. That of 

 Gomphognathus (if c^ m|.|) differs only in having more molars. 



The molars, however, retain their reptilian character. 

 They have but one tubercle and one root, except perhaps 

 those of Tritylodon, which have two, and consist merely in 

 one broadened tooth, whereas the molars of the Mammals are 

 formed by the union of several teeth. Also, side by side with 



