DESCRIPTION OF SECTIONS 
13 
DIMENSIONS OF THE OVUM. 
The ovum is completely surrounded by decidua and lies in a blood 
filled space excavated in it. The dimensions of the cavity at their 
maximum are P95 mm. in its longest diameter (parallel or approximately 
parallel to the vertical axis of the fragment of decidua figured on page 
10), ’95 mm. in depth, and IT mm. in its third dimension. The last 
measurement is arrived at by summing the number of sections 7 m thick 
in which the implantation cavity appears. The space enclosing the ovum 
is thus oval in shape, with its long axis parallel to the surface and about 
twice the length of its vertical axis, or depth from the surface. The 
dimensions of the blastocyst itself are rather difficult to determine with 
exactness owing to its wall being a little folded at several points. In 
Plate i, Fig. 1 and Plate in. Fig. 3, which represent a section well to one 
side of the equator of the vesicle, the cavity measures about ’36 mm., 
and it is approximately circular. In Plate II, Fig. 2 and Plate iv, Fig. 4, 
which is a section cutting the equator of the blastocyst, the internal 
measurements are '77 by '63 mm. in its two dimensions. The shorter 
measurement may be taken to represent the maximum size of the cavity, 
seeing that the blastocyst is obviously compressed and folded at one side ; 
it is probable that the vesicle is spherical at this stage, because the contour 
of the unfolded wall is approximately the arc of a sphere. 
GENERAL DESCRIPTION OF THE SECTIONS. 
Plate i, Fig. 1 shows the general relations of parts as revealed by a 
low power of the microscope. The section cuts the whole length of the 
decidual lobule described above. It is marked off above by a fissure which 
indicates the upper limit of the tubercle seen in Figure 1 ; below it ends 
in a rounded and slightly overlapping projection which corresponds to 
the lower edge of the papilla. The free surface of the lobule shows 
above the mouth of a gland, and over the ovum an irregular depression 
which is the orifice of the space excavated in the decidua. This does not 
