THE MOST PRIMITIVE KNOWN REPTILE. 



289 



end. The reduction seems to have taken place at the ventral 

 end of the opening. The Captorhinidae retain a very large 

 stapes. 



Sphenethmoid. — The anterior end of the brain of Seymouria is 

 surrounded by a badly known bone, which agrees exactly in its 

 main features with the sphenethmoid of Eryops, and with the 

 same bone in Pariasaurus and similar bones in other Cotylosaurs. 



Palate. — The paiate of Seymouria is in essentials identical with 

 that of the Embolomerous Labyrinthodonts. 



The resemblances depend on the identity in shape of the large 

 pterygoid, meeting its fellow in the middle line anteriorly, 

 laterally articulating with the prevomer, palatine, and ectoptery- 

 goid, and having the quadrate ramus formed by a vertically 

 standing plate reaching nearly up to the skull-roof, and bending 

 round behind the quadrate to meet the squamosal in a long 

 suture. 



This bone is covered, apparently all over, by a shagreen of 

 granular teeth in Seymouria and Pteroplax. 



The palatine of Seymouria agrees exactly with that of Terano- 

 spondyli in structure, the most striking similarity lying in the 

 tusk. This tooth is unique amongst reptiles in its mode of 

 insertion in a pit which also encloses the replacing tooth, but 

 agrees exactly with all the large palatal teeth of Stegocephalia. 



The ectopterygoid of Seymouria agrees exactly with that of 

 Eryops in contributing to a rudimentary flange which is applied 

 to the lower jaw, and consists essentially of a deflected corner 

 formed by pterygoid and transverse. The only feature of the 

 palate of Seymouria which cannot be matched in Temnospondyli 

 is the approximation of the posterior nares to the middle line. 



The palate of Seymouria differs from those of all other 

 reptiles in the presence of the palatine tusks and the very weak 

 development of the flanges which face the lower jaw r . 



The Captorhinid palate more nearly resembles that of Seymouria 

 than those of other Cotylosaurs, but differs in not having the 

 quadrate ramus of the pterygoid reaching the squamosal, in the 

 stronger transverse processes, and the loss of the palatine tusk. 

 The maxillary teeth of Seymouria exactly resemble those of 

 Temuospoudyls in being fused to their base and to a labial wall 

 of bone, in having fluted roots, and in being replaced alternately. 

 No other Cotylosaur has at all a similar dentition. 



Prof. Broili has already shown that in its genera] build, in the 

 deep otic notch, and the backwardly-inclined quadrate, and in the 

 presence of the intertemporal, the skull of Seymouria resembles 

 that of the Temnospondyls. In all these features it differs from 

 all other reptiles. 



The elongated lachrymal reaching from the orbit to the nostril 

 is, however, a reptilian characteristic known in scarcely any 

 Temnospondyl. 



The septoma.xilla of Seymouria. agrees with thai of Tern no- 



