416 THE PHYSIOLOGY OF REPRODUCTION 



of the fcefcal mesoderm in the angioflasmode, the tissue is 

 broken up into a series of labyrinthine lamellae, which consist of 

 a network of maternal vessels clothed on each side by syncytial 

 trophoblast. The meshes of the network are penetrated by 

 the vessels of the viUi. In this way, according to Duval, the 

 labyrinth is formed. In it the maternal and the foetal blood 

 are separated by the endothehum of the uterine capillaries, a 

 cellular layer (considered foetal by Duval and maternal by 

 Heinricius) which later disappears, the syncytium, mesoblast, 

 and foetal capillary walls. 



At places, however, the vilh come directly in contact with 

 maternal blood, especially at the " green border " of the placenta, 

 which forms a characteristic appearance in some of the Carnivora. 

 In aU the members of the order, larger or smaller maternal 

 haemorrhages occur at an early period after the attachment of 

 the blastodermic vesicle. The effusions vary in size and position. 

 In the dog they occur regularly along the margins of the placental 

 zone, and form the hordure verte ; in addition smaller haemor- 

 rhages take place into the substance of the placenta, and form 

 the " green pockets," which may be isolated or joined to the 

 green border by bridges (Fig. 99). In the cat, the haemorrhages 

 occur in irregular positions and do not assume the green colour 

 typical of the dog. Indications of a green border are present in 

 the earher stages, but not in the completed placenta. In the 

 otter and badger, the effusion takes the form of a large blood- 

 pouch, filled with a great variety of blood derivatives. In the 

 ferret the copditions are similar ; the main effusion occurs at 

 the anti-mesometrial border of the uterus, and divides the zone 

 into two lateral discs. According to Robinson, it hfts the 

 trophoblast from the decidua, and forces it in the form of irre- 

 gular pouches towards the interior of the ovum. Strahl and 

 Bonnet also state that the blood is effused between the mucosa 

 and the blastodermic vesicle, and thus is contained in spaces 

 whose walls are maternal on the one side and fcetal on the 

 other. According to Duval the blood-spaces are entirely hned 

 by trophoblast, and with the advance of the vilh other and 

 larger haemorrhages occur, coalescing to form the green border 

 and islands. In either case the trophoblast is in direct contact 

 with maternal blood. There the wall of the blastodermic 



