Foetal Mernbranes of the American Beaver (Castor canadensis). 



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projecting in its entirety into the cavity of the blastocyst. The 

 omphalo-m esenteric cord can be seen somewhat dimly through 

 the brown-coloured chorion. ascending to a point opposite the left 

 side of the foetus, where it abuts upon the chorion and spreads its 

 vessels over the area vasculosa. At this same point there is 

 a distinct aperture in the surface of the chorion leading into a 

 long tnbe which accompanies the omphalo-mesenteric vessels for a 

 certain distance and then ends blindly. This chorionic tnbe con- 

 tains the same brown pigment as is diffused over the outer surface 

 of the blastocyst; it is what remains at this stage of the omphalo- 

 mesenteric canal (Fig. D). 



In another specimen the chori- 

 onic vessels emerged upon the 

 surface farther forwards, in front 

 of the middle of the foetus. over 

 the shoulder-region ; the Position of 

 the point is very variable. The 

 omphalo-mesenteric cord lies in the 

 substance of the amnion, and 

 at the point where the vessels 

 enter the chorion. the latter adheres 



Fig. D. 



Fig. E. 



Fig. D. The omphalo-mesenteric cord of Fig. C, dissected out and somewhat 

 enlarged. 1. Aperture of omphalo-mesenteric canal. 2. The canal ending blindly. 

 3. Vein. 4. Artery. 



Fig. E. View of the pear-shaped area on the uterine wall behind the placenta. 

 1. Candal lobe of placenta. 2. The serotina. 3. Inner surface of uterus. 4. Line 

 of insertion of umbilico-uterine ligament. 5. Opening of inter-utricular segment. 

 6. Inner surface of uterus within the line of concrescence (utero-placental area). 



to the amnion, this being the only point where chorion and 

 amnion meet. 



