296 TROSAURIA 



the maxillary, which is long, while the anterior process of the 

 jugal is much reduced. There is no pre-orbital fossa. The nares 

 are terminal and lateral, well separated by the premaxillaries. 

 The posterior temporal bridge is formed by the squamosal and 

 parietal, the bridge extending laterally over the quadrate and 

 enclosing a wide space between itself and the buttress-like expan- 

 sion of the lateral occipital bone. The space enclosed between 

 this occipital buttress, the quadrate, and the pterygoid support 

 of the latter is likewise very large ; it is of course the cavity 

 of the middle ear, and as such is crossed by the columellar chain 

 of the ear. The infratemporal bridge or jugal arch is formed by 

 the jugal, which joins the descending process of the squamosal, 

 and by the quadrato-jugal, which is small and fused with the 

 quadrate. The latter is consequently very firmly fixed. 



The teeth are acrodont, ankylosed in one series with the 

 supporting bones, triangular and much worn down in older 

 specimens. Originally there seem to be several in the premaxilla, 

 but the adult bite with the somew r hat curved-down portions of 

 the premaxillaries themselves, or with what remains of the fused 

 bases of the original teeth, which then, together with the bone, 

 look like one pair of large chisel-shaped incisors. The lateral 

 edges of the palatines likewise carry teeth, those of the mandibles 

 fit into the long slit-like space between the palatine and the 

 maxillary teeth. Young specimens have a few small teeth on 

 the vomers, which are large, and separate the long choanae from 

 each other. The pterygoids form an anterior symphysis, posteriorly 

 they rest upon short processes of the basisphenoid and send short 

 flanges to the quadrates. 



The vertebral column is very primitive. The atlas is still 

 typically temnospondylous. The first intercentrum or fused pair 

 of basiventrals is broad and thick, and forms the ventral half of 

 the atlas-ring, which articulates with the first centrum and with 

 the second intercentrum. The irregularly shaped neural arches 

 remain separate from each other and from the centrum ; they 

 carry on the dorsal side a pair of disconnected supradorsals, the 

 so-called pro-atlas. The second intercentrum is fused with the 

 first and second centrum. The second to ninth intercentra 

 have low median ridges or knobs, and are as a rule more 

 firmly attached to the cranial ends of the centra. Those of the 

 trunk are small. From the third or fourth caudal vertebra 



