80 OBSTETRICAL PHYSIOLOGY. 



is distended with fluid, and so is separated from the foetus ; and after 

 being reflected upon the funis, of which it forms the outer coat, it 

 terminates at the umbilicus. In shape it is at first spherical, but is 

 afterwards ovoid, and it has thin transparent walls. The external face 

 is covered by the inner layer of the allantois, to which it slightly 

 adheres. The internal face is quite smooth, and applied more or less 

 directly to the skin of the foetus. It exhales or secretes a fluid — the 

 liquor amnii — which bathes the foetus, and serves an important purpose 

 in intra-uterine life. 



In the foetus, as above mentioned, the amnion is continuous with the 

 skin around the umbilicus, and is constituted by two superposed layers: 

 one, a very fine fibrous membrane that adheres to the allantois ; and 

 another, an epithelial layer, which lines the inner face of the latter. 

 At certain points of its internal surface in Solipeds, according to some 

 authorities, though denied by others, there are small white opaque 

 masses of what are supposed to be epidermic cells ; hence, this mem- 

 brane has been designated a true epidermis of the blastoderm. Though 

 thin and transparent, it is nevertheless of a firm texture, and resists 

 laceration better than the other membranes. It does not exhibit either 

 vessels or nerves when in a healthy condition. When the amniotic sac 

 is inflated, there is observed, at the portion adjoining the infundibulum 

 of the urachus, a kind of vascular plexus, having the shape of a goose's 

 foot, between the branches of which the two superposed layers are 

 much less transparent than elsewhere. At this part, between the 

 amnion and the allantois, is the small membranous pouch, quite 

 empty, in which the umbilical vesicle terminates ; and here also the 

 amniotic sac forms, opposite the cord, a little conical cul-de-sac. 

 Towards the termination of gestation, one of the extremities of the pouch, 

 corresponding to the posterior limbs of the foetus, is stretched into a 

 very short wide horn. 



LiQUOK x\mnii. 



The liquor amnii is an albuminous alkaline fluid contained in the 

 amniotic sac, in which the foetus is suspended as in a hydrostatic 

 bed. It is in greater or less quantity, according to the period of gesta- 

 tion — being abundant and limpid, or slightly lactescent, at an early 

 period ; and becoming scantier, viscid, and citron or reddish-tinted at 

 an advanced stage, when it is adhesive and agglutinates the hair. In 

 a Mare twenty-one weeks pregnant, Gurlt found two pounds twelve 

 ounces of fluid ; in another at thirty-six weeks, four pounds five 

 ounces ; and, finally, in one about the fortieth week, the allantoid and 

 amniotic fluids weighed collectively nineteen pounds and half an 

 ounce. Its colour during this period may be due to the meconium 

 thrown out from the digestive passages of the foetus ; and its composi- 

 tion doubtless varies with the development of the latter. It is some- 

 what salt to the taste, and contains 99 per cent, of water, as well as 

 albumin, mucosine, kreatin, glycose, and salts, the chief of which are 

 chlorides of sodium and potassium, and the sulphate and phosphate of 

 lime. There is also a yellow matter analogous to bile, as well as urea. 

 A peculiar acid, the amniotic, has also been found in it, in addition to 

 fragments of meconium from the intestines of the foetus, epithelial cells 

 and their nuclei, besides portions of the thick epidermis which covers 

 the plantar surface of the hoof of Solipeds. Towards the end of gestation 

 the albumin diminishes. Probably the formation of the mucous layer 



