716 



UTERUS AND ITS APPENDAGES. 



passes off in all directions at the root of the 

 cord, and spreads in a thin opaline lamina 

 over the fetal surface of the placenta, to 

 which it slightly adheres. In some cases, 

 especially when 'the umbilical vessels divide 

 before entering the placenta, the amnion has 

 no attachment at all to the latter. The am- 

 nion of the placenta does not differ in any 

 respect from the rest of the amniotic sac, of 

 which the placental portion constitutes about 

 one third. Upon its foetal surface is a single 

 layer of flattened polygonal cells filled with 

 delicate fat granulations. 



Chorion. The same proportion of chorion 

 as of the amnion, namely, about one third of 

 the entire superficies, is appropriated to the 

 placenta. This, however, is not, like the 

 amnion, simply an apposed membrane. It 

 enters into the composition of the organ, and 

 gives strength to it (fig. 484. ch). It sustains 

 and transmits the branches of the umbilical 

 vessels (vf), which adhere to, and ramify upon, 

 its foetal surface, between it and the amnion. 

 This face of the chorion is united to the amnion 

 by a thin and easily separable layer of soft 

 pulpy tissue, constituting a portion of the 

 tunica media of the ovum, while the reverse 

 surface, which forms, as it were, the base or 

 floor of the placenta, bears the numerous tufts 

 or villi that make up the bulk of this organ. 



Fcetal blood-vessels. The blood-vessels of 

 the placenta which belong to the foetus are 

 branches of the two umbilical arteries, and 

 of the single umbilical vein. These, as just 

 stated, ramify in large trunks over a consider- 

 able portion of the fetal or under surface of 

 the placenta, before they penetrate the cho- 

 rion to gain the interior of the organ. When 

 the foetal vessels have been injected from the 

 funis, their course upon this surface of the 

 placenta is easily traced. Within the root of 

 the cord, and at a distance of one inch from 

 its insertion, the two umbilical arteries com- 

 municate together by a cross branch half an 

 inch in length. Immediately on reaching the 

 placental surface, each artery bifurcates, the 

 branches passing off in opposite directions. 

 A second bifurcation takes place, in the same 

 manner, about half or three quarters of an 

 inch from the first. And lastly, a third, at 

 distances ranging from one to two and a half 

 inches. Each of these dichotomous divisions 

 is at first more or less abrupt and opposite, 

 the vessels afterwards bending, and taking a 

 slightly divergent or parallel course, or even 

 somewhat approximating. After the third 

 bifurcation, the vessels again divide and sub- 

 divide, but now at acute angles ; their extre- 

 mities become lost, when they are reduced to 

 the size of a crow quill, by dipping down sud- 

 denly, and passing through the chorion, to 

 enter the substance of the placenta at dis- 

 tances varying from an inch to an inch and a 

 half from its border. A small branch, how- 

 ever, in continuation, often runs on nearly to 

 the edge. Lateral branches, of the same size 

 as the terminal subdivisions, also leave the 

 main vessels in all parts of their course, and 

 dip down into the placental substance. 



The branches of the veins, about sixteen in 

 number, which return the blood from the in- 

 terior of the placenta, emerge from its sub- 

 stance close to the points of entrance of the 

 arteries, and take a less tortuous course than 

 the latter. They, however, accompany these 

 vessels, but more in the form of radiating 

 lines, which proceed towards the root of the 

 funis, passing under the arteries, and ulti- 

 mately uniting in the single umbilical vein. 



The varieties in the form of the placenta 

 already noticed are apparently dependent upon 

 certain modifications in the development and 

 arrangement of these vessels, which are like- 

 wise very variable, although the same primary 

 divisions are noticeable in all. In the circular 

 placenta the root of the cord is inserted into, 

 or near, the centre. In the oval form it is 

 attached to the smaller extremity forming the 

 placenta en raquette. In the reniform and 

 cordate placenta, the insertion is likewise more 

 or less lateral. Lastly, when the vessels of 

 the cord divide before arriving at the surface, 

 they form the placenta en parasol. 



Uterine surface. The reverse or uterine 

 surface of a placenta which has been sepa- 

 rated from its attachment, as in natural labour, 

 is rough, and is divided into numerous rounded 

 oval or angular portions, termed lobes or co- 

 tyledons. These vary from half an inch to 

 an inch and a half in diameter. The whole 

 of this surface consists of a thin, soft, and 

 somewhat leathery investment of deciduous 

 membrane, which dips down in various parts 

 to form the sulci that separate the cotyledons 

 from each other. This layer is a portion of 

 the decidua which, as long as the parts are 

 in situ, constitutes the boundary between the 

 placenta and the muscular substance of the 

 uterus, but which at the time of labour be- 

 comes split asunder, so that while a portion 

 is carried off along with the placenta, and 

 constitutes its external membrane, the rest 

 remains attached to the inner surface of the 

 uterus. This layer serves as a medium by 

 which the uterine arteries (fig. 484. a a) and 

 veins pass from the uterus into the placenta. 

 Numerous valve-like apertures are observed 

 upon all parts of the surface. They are the 

 orifices of the veins which have been torn off 

 from the uterus. A probe passed into any of 

 these, after taking an oblique direction, enters 

 at once into the placental substance. Small 

 arteries, about half an inch in length, are also 

 everywhere observed embedded in this layer. 

 After making several sharp spiral turns, they 

 likewise suddenly open into the placenta. 

 These are the uterine vessels, which convey 

 the maternal blood to and from the interior of 

 the placenta. 



Circumference. The margin of the pla- 

 centa is bordered all round by the united 

 membranes which enter into its composition. 

 Here the amnion and chorion, after lining the 

 fetal or concave surface, come into contact 

 with the decidua which covers its uterine face, 

 and the three membranes then pass off to- 

 gether to enclose the liquor amnii and foetus. 

 At this part the decidua is always most dense. 



