No. 2304. REPTILIAN CHARACTERS IN MAMMALS— WORTMAN. 25 



represent the final stages in the coalescence of these elements, which 

 remain free in the Macroscelididae. 



As regards the Tupaiidae the evidence in favor of the undoubted 

 presence of certain of these reptilian elements, while it is not quite 

 so direct and positive as it is in Rliyncliocyon, is nevertheless very- 

 suggestive. That the so-called postorbital process of the frontal 

 represents a distinct element is not susceptible of absolute proof at 

 present, yet there is considerable evidence in favor of such a view. 

 The single embryo skull of Tupaia which I have dissected was 

 unfortunately of too young a stage to show many of these points 

 clearly, but there is some evidence of a separate center, lying behind 

 the supraorbital foramen, which begins to ossify much later, appar- 

 ently, than the other bones of the skull. This is likewise true of the 

 bones of the jugal arch and squamosals, since in the embryo above 

 referred to no ossification in these elements had yet started. The 

 lachrymal, however, had begun to ossify and it is of great interest 

 to note that it starts from two centers, one below surrounding the 

 lachrymal canal and the other above adjoining the frontal. The 

 evidence is conclusive, therefore, that this latter element represents 

 the prefrontal of the reptile. 



In regard to the bones surrounding the so-called malar foramen 

 the only direct evidence as the case now stands is based upon the 

 anomalies already described; but when we take into consideration 

 the embryological evidence derived from the human malar quoted 

 above, from the adult condition shown in RhyncJiocyon, the evidence 

 from the embryo of Galeopterus, the embryo of the opossum, the 

 young skull of the sea cow, as well as those of so many other mammals, 

 the assumption is warranted that there are three elements represented 

 in the jugal arch of Tupaia, corresponding to the jugal, quadrato- 

 jugal, and postorbital bones of the reptilian skull, and that they are, 

 moreover, disposed around the malar foramen and form its boundaries 

 quite in the same way as they do in certain of the primates. If this 

 so-called malar foramen is thus surrounded by and forms the central 

 meeting point of these three bones, then the interesting cjuestion 

 arises as to its homology. That it is not a foramen in the ordinary 

 sense is shown in Tupaia by its large size in proportion to the rela- 

 tively small size of the structures which it transmits. This same 

 condition is seen in many apes. 



A careful comparison of this malar foramen, as thus bounded in 

 Tupaia, with the lateral temporal vacuity of such a reptilian type as 

 ProcolopJion reveals a surprising degree of similarity. Thus it will 

 be seen that in both it is placed below and more or less posterior to 

 the orbital cavity, it has an oval form and is near the beginning of 

 the jugal arch. In ProcolopJion a small sliver of the squamosal 

 excludes the upper part of the quadrato-jugal from taking any share 



