504 A. A. W. HUF.REOnT. 



high and columnar, the nuclei situated in the inner half. 

 There is a very gradual passage of these modified cells to the 

 flattened ones which form the non-placental trophoblast below 

 the annulus. At the upper rim of the annulus the passage is 

 more abrupt. The ring, which is nowhere adherent to the 

 uterine surface but distinctly curved away from it, is there 

 attached to the region of fused maternal and embryonic ele- 

 ments, against which the area vasculosa is spread out. There 

 is, in fact, no interval between the cells of the omphaloidean 

 trophoblast and those of the trophoblastic annulus. The ter- 

 minal sinus of the area vasculosa is very close to the upper 

 rim of the trophoblastic annulus (fig. 88). From the point 

 where the annulus meets the uterine wall there has been from 

 the first moment of its appearance (figs. 6 — 8, and 48 — 50) an 

 indication that cells properly belonging to the annulus pro- 

 liferate in a downward direction (aw' in these figs, and in 

 fig. 84), and are then applied against the tongue-shaped mater- 

 nal shred which has already been more than once alluded to. 

 This becomes more and more evident in later stages, and then 

 forms, as will be seen below, the permanent, also ring-shaped, 

 membranous connection between the trophoblastic annulus 

 and the outer circumference of the placenta. 



In order to form an opinion as to the physiological signifi- 

 cance of the trophoblastic annulus we shall first have to describe 

 a very peculiar phenomenon, of which the first traces appear 

 about the time of the completion of the amnion, during the 

 congestion of the tissues consequent upon the gradual com- 

 pletion of the omphaloidean circulation. The histolytical pro- 

 cesses which at the time of this congestion are in full activity, 

 and which have partly contributed to prepare this circulation 

 of maternal blood outside the area vasculosa, are undoubtedly 

 connected with this phenomenon. It is an actual haemorrhage 

 which is invariably found to a lesser or greater extent just 

 outside the trophoblastic annulus, between it and the perma- 

 nent and the proliferated epithelium. As early as the stage of 

 uterus No. 51 (figs. 8, 9, and 50) there are traces of it. In 

 the last-named figure the extravasate is as yet insignificant; in 



