142 REPTILIA. 



cranial axis by the pterygoids (compare fig. 86 B, p. 134, with 

 fig. 94 B, p. 149) mark this higher grade. If this feature in the 

 palate has always been distinctive, Palceohatteria, from the 

 Lower Permian of Saxony, is the earliest member of the Class 

 Reptilia hitherto discovered ; and it is certain that during 

 the Upper Permian age there were numerous reptiles both in 

 Europe and America, probably also in South Africa. 



As the various groups become differentiated and specialized, 

 the most conspicuous of the fundamental modifications in the 

 skeleton occur in the postero-lateral regions of the skull, where 

 the bones surrounding the temporal and rnasseter muscles and 

 those supporting the lower jaw are variously rearranged in 

 separate bars and partly disappear. The form of the otic 

 region changes, while the squamosal plate, which directly 

 covers this mass in fishes (and presumably in Stegocephalia), 

 is thrust from all connection with it except at the hinder 

 angle, and its larger portion is a free bar over the muscles, 

 connected with the other plates of the cheek. In one great 

 group of reptiles, comprising the Anomodontia, Sauropterygia, 

 Chelonia, and Ichthyopterygia (fig. 91 B, c), this outward 

 thrust of the squamosal first begins, and is the sole modifica- 

 tion of the primitive type; though the cheek-plates in the 

 broad arch thus formed may be variously fused together, some- 

 times even irregularly perforated showing at first, indeed, the 

 usual inconstancy of a new and not completely established 

 feature. From the earliest members of this prime division 

 of reptiles, Palaeontology seems to demonstrate that the 

 Mammalia (with one robust zygomatic arch) arose ; some of 

 the skeletons belonging to this division might, indeed, be 

 claimed as actually mammalian, if it were not for the com- 

 plexity of the mandible and the presence of a free quadrate 

 b<?ne. In a second group, comprising the Rhynchocephalia, 

 Dinosauria, Crocodilia, and Ornithosauria (fig. 91 D), there is 

 the same arrangement of the squamosal, while the broad arch 

 of cheek-plates is pierced by a more or less extensive vacuity 

 (" lateral temporal vacuity"), which leaves a narrow bar above 

 and another narrow bar below. By the constant loss of the 

 lower, and the frequent loss of the upper bar, this group 



