366 MINOT. [Vor. II. 
allantois has grown forth and attached itself to the placenta. 
The relations of the extra-embryonic structures have been repre- 
sented by Bischoff in the diagrams of Pl. XVI. of his classical 
memoir on the development of the rabbit. These diagrams have 
since been reproduced again and again, sometimes with modifi- 
cations as notably by Kolliker in his manual, and by Van Bene- 
den and Julin. Guided by these and by my own preparations I 
venture to construct a new diagram, Pl. XXIX., which I hope 
will approximate more nearly to the actual relations of the parts, 
with which we are now concerned. 
In the first place it is to be noted that most of the section is 
occupied by uterine tissue:—compare Fig. 9, Pl. XXVIII. 
The largest space is occupied by the placenta, on the surface of 
which is situated the embryo, lying upon its side. Opposite 
(above in the figure) the embryo is the ob-placenta, 06-p/, with 
its central area, containing the monster cells, zo c/; the inferior 
wall of the yolk sack is fitted upon, but not attached to, the ob- 
placental surface. The peri-placenta, PP, appears as the con- 
tinuation of the outer zone, oz, of the placenta; it has no 
glands: its blood-vessels are enlarged, and all the space between 
them is filled with uninucleate decidual cells. This description 
of the peri-placental structure applies also to the outer zone, az, 
of the placenta. A narrow space separates the surface of the 
peri-placenta from the side of the glandular zone, ¢/, of the pla- 
centa: the letters a and 4 lie in this space. The placenta con- 
sists of three zones: 1°, the upper glandular zone, g7/, divided 
by a fissure, #, into two lobes. This fissure is partly filled with 
an ingrowth of embryonic mesoderm, mes; the transversely 
expanded bottom of the fissure forms the sub-placenta, sd.p/; 
the glandular zone as a whole constitutes a protuberant mass 
with top and sides clearly distinguishable. Below the sub-pla- 
centa is the sub-glandular zone, s.-g/z, with dilated blood-vessels 
and multinucleate decidual cells. 
The embryo lies upon the surface of the placenta. From its 
ventral side spring the allantois, a//, and the stalk of the yolk 
sack ; for the sake of clearness the amnion and pro-amnion are 
entirely omitted, since they have no direct relation to the 
uterus.! The allantois expands upon the placenta; the yolk 
1 For diagrams of the pro-amnion, etc., see Van Beneden et Julin. Copies of 
their figures are given in Buck’s Reference Handbook of the Medical Science, V1., 32. 
