AMNIOTIC FLUID. 805 



cal cord, which connects the embryon with the placental portion of the 

 chorion, and the umbilical vesicle, formed from the same layers as the allan- 

 tois. 3. The amnion, which is the internal layer of the amniotic fold, per- 

 sisting throughout foetal life. 4. The embryon itself. 



During the early stages of development of the umbilical vesicle and the 

 allantois, the internal amniotic layer, or the true amniotic membrane, is 

 closely applied to the surface of the embryon, and is continuous with the epi- 

 dermis, at the umbilicus. It is then separated from, the allantois by a layer 

 of gelatinous matter ; and in this layer, between the amnion and the allan- 

 tois, is the umbilical vesicle. At this time the umbilical cord is short and 

 not twisted. As development advances, however, the intermembranous gelat- 

 inous matter gradually disappears ; the cavity of the amnion is enlarged by 

 the production of a liquid between its internal surface and the embryon ; and 

 at about the end of the fourth month, the amnion comes in contact with the 

 internal surface of the chorion. At this time the embryon floats in the 

 amniotic cavity, surrounded by the amniotic fluid. 



The amnion forms a lining membrane for the chorion. By its gradual 

 enlargement it has formed a covering for the umbilical cord ; and between 

 it and the cord, is the atrophied umbilical vesicle. The amnion then resem- 

 bles a serous membrane, except that it is non-vascular. It is lined by a 

 single layer of pale, delicate cells of pavement-epithelium, which contain a 

 few fine, fatty granulations. At term the amnion adheres to the chorion, 

 although it may be separated, with a little care, as a distinct membrane and 

 may be stripped from the cord. From its arrangement and from the absence 

 of blood-vessels, it is evident that this membrane is simply for the protec- 

 tion of the fcetus and is not directly concerned in its nutrition and devel- 

 opment (see Plate II, Fig. 2). The gelatinous mass referred to above, situ- 

 ated, during the early periods of intrauterine life, between the amnion and 

 the chorion, presents a semi-fluid consistence, with very delicate, interlacing 

 fibres of connective tissue and fine, grayish granulations scattered through 

 its substance. These fibres are gradually developed as the quantity of gelat- 

 inous matter diminishes and the amnion approaches the chorion, until 

 finally they form a rather soft, reticulated layer, which is sometimes called 

 the membrana media. 



Amniotic Fluid. The process of enlargement of the amnion shows that 

 the amniotic fluid gradually increases in quantity as the development of the 

 fcetus progresses. At term the entire quantity is variable, being rarely more 

 than two pints (about one litre) or less than one pint (about half a litre). 

 In the early periods of utero-gestation it is clear, slightly yellowish or green- 

 ish, and perfectly liquid. Toward the sixth month its color is more pro- 

 nounced and it becomes slightly mucilaginous. Its reaction usually is neutral 

 or faintly alkaline, though sometimes it is feebly acid in the latest periods. 

 It sometimes contains a small quantity of albumen, as determined by heat 

 and nitric acid ; and there generally is a gelatinous precipitate on the addi- 

 tion of acetic acid. The following table gives its chemical composition 

 (Robin) : 



