THE TEMPORAL ARCHES OF THE REPTILIA. 1 8/ 



is no evidence, in my opinion, that the large eye-opening has 

 been formed by the coalescence of the supratemporal and orbi- 

 tal vacuities, but rather by the extension backward of the orbit, 

 through the absorption of the postorbital bones. At the poste- 

 rior part of the skull is seen an element which was believed by 

 Seeley 1 to be the epiotic, a bone otherwise unknown, save possi- 

 bly in some anomodonts, in the higher reptilia. Woodward, 2 

 however, identifies this bone as the squamosal, and the so-called 

 squamosal in front of it he cails the prosquamosal. I do not feel 

 at all sure which view is correct. If the two elements are really 

 the epiotic and squamosal of the cotylosaur skull, I fail to under- 

 stand how Procolophon could have stood in any very intimate 

 relations with the early rhynchocephaloid reptiles, for they primi- 

 tively had a prosquamosal. Professor Osborn states that all the 

 elements of the cotylosaur skull are present in Procoloplion, 

 but neither his figure, nor Seeley's nor Broom's descriptions indi- 

 cate the presence of all three bones, the epiotic, squamosal and 

 prosquamosal one of these elements seems certainly to be 

 absent. Between the postorbital and the squamosal, there is a 

 small vacuity shown in the original figure of this reptilian skull, 

 the one reproduced here, which has been believed to be the latero- 

 temporal fenestra. But, if I am correct, Dr. Broom denies the 

 presence of this opening, and the figure he has been kind enough 

 to send me shows no laterotemporal vacuity, in that position at 

 least. Are we to suppose, such being the case, that, in addition 

 to the absence of a supratemporal vacuity, the lateral opening 

 also has been closed up secondarily? It seems to me that such 

 reasoning savors a little too strongly of the ante-Baconian 

 methods. 



While Procolophon is shown by Broom, from certain evident 

 peculiarities of the skull and skeleton to be more nearly related 

 to the Rynchocephalia than to the Anomodontia, I fail to see any 

 striking resemblances in the temporal region. It is a diapsid 

 without temporal fenestrae. 



Perhaps the most primitive known of the truly rhynchocepha- 

 loid type of reptiles, so far as the temporal region is concerned, 



^ Phil. Trans., 1889, p. 271. " It rests by a squamous overlap upon the poste- 

 rior border of the squamosal, and the external surface of the parietal.' 

 2 " Vertebrate Paleontology," p. 149, Fig. C. 



