202 Arthur Willey, 



As the umbilico-uterine concrescence is perhaps the 

 most original Observation in connection with the foetal membranes 

 of the beaver, the facts may be stated more clearly. On opening 

 a foetal Chamber of the uterus, the foetus is found surrounded by 

 a brown vascular membrane which adheres to the uterine mucosa 

 along the raesometric side by a cephalad adhesion, a placental ad- 

 hesion, and a caudad adhesion. The two terminal adhesions are 

 pear-shaped in contour, and embrace the intervening constricted 

 parts of the uterus i. e. the inter-utricular passages. On cutting 

 through the umbilico-uterine membrane which effects the cephalad 

 concrescence, a transparent membrane,. the anterior umbilico-placental 

 membrane, is exposed, with a yellow fluid pressing upon it from 

 the interior of the blastocyst. Similarly on cutting through the 

 caudad adhesion, the posterior umbilico-placental membrane is ex- 

 posed, with the same yellow fluid showing through it. Both mem- 

 branes, or rather both parts of the same membrane, are continuous 

 with the rest of the chorion along the line of origin of the umbilico- 

 uterine suspensory ligament. 



An incision through the vascular chorion opens up the main 

 cavity of the blastocyst, the exocoelom, in which the embryo is 

 carried closely invested by a thin transparent non-vascular membrane. 

 the amnion. The yellowish fluid first seen and mentioned above, 

 was mostty contained in the space between chorion and amnion, 

 i. e. in the exocoelom. But a little of the fluid was present in the 

 amniotic cavity, where of course it constituted the liquor amnii. 

 In another specimen most of the fluid was contained within the 

 amnion, i. e. in the amniotic cavity, between the amnion and the 

 body of the foetus. Thus on cutting through the hinder part of the 

 chorion and holding the foetus up by the head, all the yellow fluid 

 escaped from the exocoelom, but there was still some fluid left within 

 the amnion like that in the outer sac. It is an albuminous fluid 

 giving abundant coagulum when treated with Millon's reagent. The 

 amnion therefore acts as an osmotic membrane stretched between 

 the exocoelom and the amniotic cavity. 



In the case of another foetus taken from the second pregnant 

 female, all the yellow fluid was contained within the amnion which 

 was greatly distended, Alling up the greater part of the exocoelom. 



The line of insertion of the umbilico-uterine ligament into the 

 wall of the uterus circumscribes a pear-shaped area about 2 J / 2 inches 

 (upwards of 60 mm) in length, extending beyond the placental region 



