CHANGES IN THE OVUM. yj 



external layer of the blastoderm. It envelops the embryo very closely at 

 an early period, and is continuous with the common integument of the 

 foetus at the open abdominal parietes. At a later period it 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 umbil- 

 icus. 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 au- 

 thorities, though denied by others, there are small white opaque masses 

 of what are supposed to be epidermic cells ; hence, this membrane has 

 Deen 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 observ^ed, 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 membraneous pouch, quite empty, in which the um- 

 bilical 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 sac corresponding to the posterior limbs of 

 the foetus, is stretched into a very short wide horn. 



Liquor Amnii. 



The liquor amnii is an albuminous alkaline fluid contained in the am- 

 niotic sac, and in which the foetus is suspended as in a hydrostatic bed. 

 It is in greater or less quantity, according to the period of gestation : 

 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 color during this 

 period may be due to the meconium thrown out from the digestive pas- 

 sages of the foetus ; and its composition doubtless varies with the devel- 

 opment of the latter. It is somewhat salt to the taste, and contains 99 

 per cent, of water, as well as albumen, 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 a7niiiotic, 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 face of the hoof of solipeds. Towards 



