398 MINOT. [Vou. II. 
commencement of the perivascular coats, at least of the larger 
vessels, the matrix being quite dense around them, and the cells 
elongated almost into fibres, and possessing a slightly increased 
affinity for coloring-matters. The larger blood-vessels and 
unmetamorphosed part of the layer occupy a middle portion be- 
tween the two surfaces, but the smaller blood-vessels lie near 
the ectoderm (compare Cut 19, v), thus presaging the formation 
of Langhans’ vascular layer (Gefassschicht). The development 
of the mesoderm of the chorion leve stops at about this stage, 
or at the stage when the matrix has completely changed from 
its first state; in the region of the frondosum, however, develop- 
—s 2 oy; = SS i! ass SD Oeecn 
SE ons eNOS if BS fang Gh 
ny NS A f a\h I, is aes 
as 
Cut 20.— Section of the amnion and placental chorion of the fifth month. £9, 
amniotic epithelium; Am, amnion; Str, stroma; /70, fibrille layer; /ér, fibrine 
layer; c, cellular layer; Vz, villi. (From a section cut in celloidine, and stained 
with Weigert’s Hzmatoxyline. The drawing is only approximately correct as to 
details. XX 71 diams.). 
ment proceeds much further by the production of fibres throug 
out the whole of the layer; usually, but not invariably, the fibres 
become much more numerous near the ectoderm than in the 
inner part of the mesoderm, thus differentiating a well-marked 
sub-epithelial fibrillar layer, Cut 20, 76, from the deeper and 
wider stroma, S¢v. The fibrillar layer is that commonly spoken 
of as the connective tissue layer of the chorion: for details of 
its structure, including the “‘ Gefassschicht,’ see Langhans and 
