PROFESSOR W. TURNER ON THE PLACENTATION OF THE APES. 
551 
extent of the placental surface of the human chorion, consisting of homogeneous 
intercellular substance with cells scattered in it. This layer also, he stated, invested 
the steins of the villi, but was not prolonged on to their finer branches. From its 
arrangement he regarded it as bounding the maternal blood spaces on the foetal side 
of the placenta, and as formed of maternal tissue. This structure has recently been 
investigated by Kolliker, who named it “decidua subchorialis.” * Though recognising 
that the placental surface of the chorion presented throughout a peculiar lamellatecl 
structure, Kolliker was unable to trace the decidua subchorialis for more than a 
ghort distance from the border of the placenta ; neither was he able to see tliaf it gave 
a covering to the stems of the villi, except to those which arose from the chorion in 
close proximity to the placental border. Throughout the placenta generally he states 
that the maternal blood spaces had on their foetal aspect no other boundary than the 
chorion itself. Leopold, in his memoir on the human placenta already referred to, 
sayst that his observations correspond with those of Kolliker. But a different 
view of the nature of this structure has been advanced by Langhans.| He recognises 
that about the middle of pregnancy a layer of cells is developed. At first the cells 
are small in size, but subsequently present a great resemblance to decidual tissue, 
though in his opinion they do not belong to the decidua. For he states that they 
are formed between the vascular fibrillar stroma of the chorion and its epithelial 
covering, and are probably derived from the vascular layer of the chorion itself. He 
names the structure the “cell layer of the chorion frondosum,” employing a term which 
implies no opinion of the origin of the cells. In most cases the layer is not of equal 
thickness throughout, but the cells lie in groups, between which a homogeneous 
intercellular substance is situated, which is directly continuous with the fibrillar tissue 
of the chorion. At a later stage of placental growth lie states that this cell layer 
becomes converted into canalised fibrine, for after the dissolution of the chorionic 
epithelium in the last months of pregnancy a deposition from the maternal blood 
takes place, and the lamellated layer of the chorion frondosum is formed. This cellular 
and lamellated layer bounds the space within the placenta in which the maternal 
blood is contained, and it is penetrated by the chorionic villi which project into that 
blood space. 
My attention has also been directed to the placental surface of the chorion in the 
human placenta. In the placenta in the fifth month this surface was covered by a 
single layer of cells, which had the asjiect of the chorionic epithelium. They were, 
however, to all appearance in process of degeneration, for they were infiltrated with 
fine granular particles. In a placenta in the seventh month, although this surface of 
the chorion was obscured by masses of blood corpuscles, and by a granulated material 
of indefinite structure, which might have been fibrine, here and there patches of cells 
* ‘ Entwicklungsgescliichte,’ ed. 1876, p. 337. 
t Op. cit., p. 52. 
t Op. cit., p. 256. 
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MDCCCLXXVIII. 
