782 General Notes. ei) | 
grown, it is very evident that there is an annular thickeningd $ 
the uterine wall (shown at v in A and B of Fig. 1). Dissecim $ 
reveals the fact that this annular thickening is nothing else tia {i 
a part of the decidua, as it is closely adherent to the foetal mm $i 
branes, and extends from either edge of the decidua of the & fi 
coidal placenta (f) around over the back of the embryo, as shom $ 
at B and C in Fig. 1. This thickened portion, or decidua, fF 
isolated, together with the placenta, aig 
unrolled upon a flat surface, would appx $ 
as shown at D in Fig. I. e qusur E 
immediately arises, What is the nature d | 
this structure? It seems to the writer tht i 
there can be no question that its positiona | 
relations indicate that it is a vestige of the zonary type of placet. 
which must have been developed in the ancestors of the Ro 
All of the placental girdle, in the light of this evidence, * 
been aborted in the Rodentia, except a small discoidal so") 
nearest to the blood vascular supply on the mesometric ee 
the uterus, as shown at A in Fig. 1, where @ repres ay 
_ Uterine artery (the vein has not been indicated in this %3 a 
. The functionless part of the decidual girdle in existing M 
_ types shows that the ancestral Rodentia possessed a zonat i 
CNR, We may confidently affirm this, in spite of the anom | 
Aa of development of the Cavys and Murine type: opn 
aS is good reason to suppose that the types of devel t b 
Laie by both the latter have been derived by eer 
wioch ans n from a type approximating the more prin pat | 
ot | was similar to the less specialized mode of de 
_ We may suppose, further, that the zonary girdle first 27 
narrow and abort on the side of the ie tube oppe 
: : con 
a agrammatically in Fig. 2, at A, where % n 
o he wall of the left and w that of the right uterine tube, 
