34 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol,. 5T. 



the condyle from the remainder of the ramus that it does not seem 

 possible that it is altogether accidental. These same appearances aro 

 likewise seen in the young jaws of many other orders of mammals^ 

 and until such time as it can be shown by actual embryological 

 investigation that these appearances are wholly deceptive and that, 

 no ossification ever takes place within the cartilagmous mold of tha 

 condyle we must continue to hold that it is not only possible but 

 highly probable in some species of mammals at least. 



From my experience in the examination and study of commencing 

 ossification of the bones in mammals I have been especially impressed 

 with the absohite necessity of selecting embryos of the proper stages- 

 of development in order to 



demonstrate any given point t^ua^/ ,«?^7^ v«/'?/^ 



beyond possible doubt, and this 

 among the rarer forms is by 

 no means always convenient or 

 an easy matter. In attempt- 

 ing to follow out this subject 

 of the presence or absence of 

 a separate and distinct center 

 of ossification in the 

 cartilaginous matrix 

 of the mandibular 

 condyle of the mam- 

 mal, I am led to 

 conclude that if ever 

 it is present, which 

 is more than likel}'', 

 it is at best but 

 feebly developed 

 and is quickly over- 

 shadowed by the 

 ingrowth of the 

 osteogenic membrane of the dentary, and all vestiges of it oblit- 

 erated. 



In view of the facts and arguments above set forth, how premature 

 appears the sweeping statement of Gregory to the effect that embry- 

 ology gives no warrant for the belief that the mammalian jaw is com- 

 posed of more than a single piece, already quoted. His second pos- 

 tulate in regard to the so-called Triassic and Jurassic mammals, if 

 indeed they are mammals at all, does not appeal to me as having 

 much weight. Out of all that are known, how many of them are 

 sufficiently preserved to show the condyle at all, and of those that 

 are thus sufficiently perfect how many are of a suitable age to show 

 the sutures even if they had been present in the earlier stages of 



B y/. 



Fig. 13.— Talpa europaea. After Parker. A, advanced stage- 



OF DEVELOPMENT OF TaLPA EUROPAEA. B, YOUNG STAGE OF DEVEL^ 



OPMENT OF SAME. Artic, ARTICULAR; In., INCUS; ^fall., malleus; 

 Man. M., manubrium of malleus; Meek. Cart., Meckel's car- 

 tilage; Quad., quadrate; Ty., tympanic. 



