No. 2304. REPTILIAN CHARACTERS IN MAMMALS— WORT MAN. 23 



skull, but it still clings to its original position, as far as its relations 

 to the squamosal, jugal, and, as we shall presently see, to the quad- 

 rate, are concerned. In Procolophon the quadrato-jugal is a rela- 

 tively large deep bone, and the similarity of this element in the two 

 forms is not very close. Its position corresponds in the two, how- 

 ever, almost exactly. 



By exclusion, therefore, the remaining element entering into the 

 composition of the jugal arch in RJiynchocyon must represent the 

 jugal bone of the reptilian skull. Its position and relations are again 

 in strict accord with the corresponding element in Procolophon and 

 other Reptilia, namely, it lies above the quadrato-jugal at its pos- 

 terior end, it passes under the edge of the squamosal behind, and in 

 front it forms the lower edge of the orbit, overlying the posterior end 

 of the maxillary and passing forward on the orbital rim to join the 

 lachrymal. All these relations, it may be added, are typically rep- 

 tilian. 



In view of the uncertainty of a division of the lachrymal by the 

 imperfect suture above described, in connection with that bone, it 

 may not be wise, with the present material, to attempt to establish 

 any homology with a distinct reptilian element. However, if the 

 embryology or the development of the lachrymal in Khynchocyon 

 finally shows it to be derived from two centers, as this suture would 

 seem to indicate, then in that event the upper element lying between 

 the frontal and lachrymal would undoubtedly have to be homologized 

 with the prefrontal or adlacJirymal of the reptilian skull and the 

 lower piece containing the lachrymal canal would represent the true 

 lachrymal. 



If this latter homology is established, what, then, is the significance 

 of the small bone lying at the junction of the frontal, lacyrhmal, and 

 maxillary on the side of the face? Its baclvward extension by a 

 pointed extremity toward the rim of the orbit would seem to indicate 

 a former position in connection with the eye cavity, and as it lies 

 above the lachrymal I have been disposed to consider it homologous 

 with the prefrontal of the reptilian skull. The relatively large size 

 and a position much nearer the orbit of a bone which is occasionally 

 seen in Dasypus, as already described, would seem to favor this view. 

 On the other hand, as we have aheady seen in the Sirenia, there is a 

 pair of ossicles lying above the lachrymals, between them and the 

 frontals, which undoubtedly represent the prefrontals for reptiles, and 

 an additional pau% lying upon the outside, and below the vestigial 

 nasals, which I take to represent the septo-maxillaries of many rep- 

 tiles, of the monotremes, and Tritilodon, as figured by Broom. It 

 may be possible, therefore, that the bones in question in RJiynchocyon 

 may represent the septo-maxillaries, but their wide separation from 

 the nasals would be against this interpretation. Whatever elements 



