No. 2304. REPTILIAN CHARACTERS IN MAMMALS— WORT MAN. 13 



obliterate all traces of sutures at a comparatively early period. A 

 dearth of material of the proper age prevents a very satisfactory 

 study of the subject in this group, but fortunately some embryos 

 give additional light. The dissection of a young embryo skull shows 

 that the lachrymal ossifies from a single center; that there is a sepa- 

 rate center for the postorbital process of the frontal; that there are 

 separate and distinct centers for the jugal, quadrato-jugal, and post- 

 orbital of the zygomatic arch. Parker's figures do not show these 

 elements in the embryo, but in my own dissection they can all be 

 distinctly made out. Parker's figures do show, however, that the 

 condylar portion of the lower jaw is made up of a separate piece * 

 (fig. 8). My material is evidently of a considerably younger stage 

 than that figured by him and is not sufficiently advanced to make 

 this out very distinctly. As for the element in connection with the 

 malleus and the tympanic I have not 

 found any satisfactory evidence of 

 its presence. 



Marsupials. — In this group of 

 mammals a number of reptilian 



characters are met with, similar to ^=^^^^"~ I ^^^^^' 



those already described in the In- 

 sectivora. In the Virginia opossum 

 the embryo skull shows that there ^i^- s.— galeopteeus philippensis. aftee 



n-T T .• ,• ■ 1 (.,1 Parker. Artie, articular. 



IS lairly distmctive evidence oi the 



presence of a prefrontal lying near the anterior part of the orbit 

 between the lachrymal and nasal; it shows, moreover, in a rather satis- 

 factory way that the malar of the zygomatic arch is made up of two 

 pieces which ossify from distinct centers, with the existence possibly of 

 a third center at the junction of the squamosal and malar. This latter, 

 however, is not certain. Of the element developed in connection with 

 the tympanic ring and the iwocessus gracilus, it may be said that in 

 the fetal sloiU it develops from a distinct center in the premallear 

 tract of Meckel's cartilage and is separated by suture from the riro- 

 cessiis gracilis up almost to the adult stage, when it usually becomes 

 coosified with the malleus. Not infrequently, however, it remains 

 distinct throughout the life of the animal. It never, apparently, co- 

 ossifies with the tympanic with which it has the same general rela- 

 tions as already described in the Insectivora. 



In other predaceous Marsupials, notably Sarcophilus, the jnocessus 

 gracilis appears to be made up as in the opossum of an unusually 

 long slender curved rod of bone, which hooks over the tympanic and 

 protrudes forward with a free extremety. Examination of a half- 



i Philos. Trans. Royal Soc. London, 1886, vol. 176, pi. 38, fig. 4. 



