THE MOST PRIMITIVE KNOWN REPTILE. 



297 



8. In the narrowing of the face. 



9. In the loss of the palatine tusks. 



10. In the better development of the ptery go-transverse 



flanges. 



11. In the lateral compression of the quadrate so that its 



horizontal section is no longer U-shaped. 



12. In such reduction of the pterygoid that it no longer 



reaches the squamosal. 



13. In a considerable compression of the lower part of the 



articular. 



14. In the loss of the two anterior coronoids and the post- 



splenial. 



15. In the somewhat more modified axis. 



16. In the presence of two sacral vertebra?. 



17. In the development of single-headed ribs. 



18. In the reduction of the intercentra. 



19. In the development of a coracoid in addition to the pre- 



coracoid. 



20. In the reduction and loss of ornament of the lower parts 



of the clavicles and the anterior end of the interclavicle. 



21. In the loss of the long posterior extension of the dorsal 



part of the ilium. 



22. In the more advanced humerus. 



23. In the loss of the long adductor crest in the femur. 



24. In the fusion of the intermedium and the tibiale. 



25. In the obliteration of the otic notch by the swinging 



backward of the upper end of the quadrate, so that the 

 posterior end of the skull seems cleanly truncated. 



Thus the Captorhinids alone amongst Cotylosaurs present 

 definite significant resemblances to Seymouria, which in the case 

 of the palate are due merely to the retention of a primitive 

 structure, but in the important characters of the fenestra ovalis 

 and the vertebra? are due to the possession by both types of a 

 structure which is certainly not derived from amphibian ancestors. 



The position and character of the fenestra ovalis common to 

 Seymouria and Captorh'mus is preserved throughout the whole 

 series of mammal-like reptiles, the Pelycosaurs and all the later 

 S. African types. This fact is clearly illustrated in the drawings 

 of text-fig. 15, where the stapes is indicated by shading. 



This position of the fenestra is of course connected with that 

 restriction of the inner ear to the lower part of the side wall of 

 the brain-case which I have shown to be one of the most constant 

 and significant characters of the Anomodontia, and one which is 

 entirely restricted to them and the Captorhinids, which Prof. 

 Williston and the writer believe to be their ancestors. Com- 

 parison of the occipital views of skulls in text-fig. 15, with similar 

 drawings of any other reptiles, will bring out the difference 

 between the two types of structure of this region clearly. 



Apart from the Captorhinids, only Limnoscelis and Seymouria 



