Findings

Abstract

If we plot the measured values of the total villous surface area (S_T) against the development age, in linear coordinates, we obtain a family of data points rising towards the right (Figs. 1–4). In other words, in all the species studied, the total villous surface area increases in the course of development of the placenta. The general trend of the data points can be represented in linear coordinates by a fitted parabolic smoothing curve. In other words, the rate of growth of the total villous surface area increases with time (acceleration). This applies to all the species studied, except the cat (Fig. 3). Figs. 3 and 4 each show the data for two species, plotted in the same coordinate system. The unequally steep rises of the curves show that the rate of growth of the total villous surface area is not the same in all species. For example, the overall growth is faster in the cow than in the horse (Fig. 4). These graphs also give a rough idea of the total villous surface area of full term placentas, e. g., about 12 m² in humans (Fig. 3). In the case of the cow the graph had to be cut short in order to fit it into the same diagram as the data for the horse (Fig. 4), but the size of the total villous surface area of the full term placenta can be read off Figs. 27 and 37 (about 130 m²). It can thus be seen that considerable inter-specific differences also exist in respect of the total villous surface area of the full term placenta.