PROFESSOR W. TURNER ON THE PLACENTATION OF THE APES. 
555 
rous branches, yet diminished but slightly in thickness in their passage to the decidua ; 
but in the human placenta they divided much more completely into branches, and 
these branches, with their finer offshoots, reached the decidua. In both, the villi were 
adherent to the decidua, and at the points of adhesion were imbedded in that struc- 
ture. In the Macacus, however, the adhesion seemed to be firmer than in the human 
placenta, and the decidual cells were prolonged for a greater distance over the villi. 
The villi are, therefore, in both placentee attached both at their chorionic and decidual 
ends, so that numerous checks are interposed to the too great separation of the chorion 
and the placental decidua from each other, such as might arise if the blood were 
poured too rapidly into the intra-placental maternal blood spaces, and the villi were 
floating free. In the human placenta, where on account of its greater magnitude an 
additional check may be needed, it is supplied by the passage of the inter-cotyleclo- 
nary dissepiments through the placenta to the chorion. 
The relatively large interval between the stems of the villi gives room for the rami- 
fications of the numerous branches of the villi with their lateral and terminal bud-like 
offshoots. In both the human placenta and that of the Macacus the buds closely 
resembled each other both in form and size, and, in both, the capillary terminations of 
the umbilical arteries had a similar arrangement in loops and coils within the buds. 
In both, an extra-villous network of capillaries was situated in the placental part of 
the chorion in the intervals between the bases of origin of the stems of the villi. 
This extra- villous network corresponded in its position to the extra-villous capillary 
network, which I have elsewhere described, in the diffused and cotyledonary forms of 
placenta. 4 ' In neither, however, did I observe an extension of the capillary network 
into the non-placental parts of the chorion such as occurs in the zonary placenta ; but 
the non-placental part of the chorion of Macacus was traversed by the branches of the 
umbilical arteries and vein, which passed between the placental lobes. 
Both in the human placenta and in that of the Macacus an intra-placental system 
of spaces for the circulation of the maternal blood was present. These spaces formed 
an irregular but freely communicating anastomosis interposed between the villi. They 
were bounded on the chorionic aspect by the sub-chorionic cells ; on the decidual 
aspect by the decidua placentalis ; whilst the spaces between the villi were bounded 
by the villi themselves with their cellular covering,, In the human placenta the 
curling arteries pass in so tortuous a manner through the placental decidua that they 
are followed with difficulty. If they previously be injected from the uterine arteries, 
in specimens where the placenta is attached to the wall of the uterus, they can, with 
the aid of a lens, be followed through the decidua. The delicate coat of the artery 
can be slit up with a needle, and the plug of injection can be followed into the 
interior of the placenta. Another way of observing their mode of opening into the 
placenta is to cut off the portion of decidua placentalis in which a curling artery is 
situated, to remove the villi attached to its placental aspect, and then to examine 
* Lectures on the Comparative Anatomy of the Placenta, already cited. 
