MAMMALIA. 207 



At the edge of the placental zone there is a very small portion of the 

 uterine mucous membrane reflected over the non-placental part of the 

 chorion, which forms a small reflexa analogous with the reflexa in Man. 



The Carnivora generally closely resemble the Dog, but in the Cat the 

 whole of the maternal part of the placenta is carried away with the fetal 

 parts, so that the placenta is more completely decicluate than in the Dog. 

 In the Grey Seal (Halichcerns yr>/ph><s, Turner, No. 219) the general 

 arrangement of the fetal membi'anes is the same as in the other groups 

 of the Cai-nivora, but there is "a considerable reflexa developed at the edge 

 of the placenta. The fetal part of the placenta is divided by a series of 

 primary fissures which give off secondary and tertiary fissures. Into the 

 fissures there pass vascular laminje of the uterine wall. The general sur- 

 face of the fetal part of the placenta between the fissures is covered by a 

 greyish membrane formed of the coalesced terminations of the fetal villi. 



The structure of the placenta in Hyrax is stated by Turner (No. 221) 

 to be very similar to that in the Eelidse. The allantoic sack is large, and 

 covers the whole surface of the subzonal membrane. The auiniou is also 

 large, but the yolk-sack would seem to disappear at an early stage, instead 

 of persisting, as in the Carnivora, till the close of fetal life. 



The Elephant (Owen, Turner, Chapman) is provided with a zonary 

 decicluate placenta, though a villous patch is present near each pole of the 

 chorion. 



Turner (No. 220) has shewn that in Orycteropus there is present a zonary 

 placenta, which differs however in several particulars from the normal 

 zonary placenta of the Carnivora ; and it is even doubtful whether it is 

 truly deciduate. There is a single embryo, which fills up the body of the 

 uterus and also projects into only one of the horns. The placenta forms a 

 broad median zone, leaving the two poles free. The breadth of the zone is 

 considerably greater than is usual in Carnivora, one-half or more of the 

 whole longitudinal diameter of the choriou being occupied by the placenta. 

 The chorionic villi are arborescent, and diffusely scattered, and though the 

 maternal and fetal parts are closely interwoven, it has not been ascer- 

 tained whether the adhesion between them is sufficient to cause the ma- 

 ternal subepithelial tissue to be carried away with the fetal part of the 

 placenta at birth. The allantois is adherent to the whole chorion, the 11011- 

 placental parts of which are vasciilar. In the umbilical cord a remnant of 

 the allantoic vesicle was present in the embryos observed by Turner, but in 

 the absence of a large allantoic cavity the Cape Ant-eater differs greatly 

 from the Carnivora. The ainnion and allantois were in contact, but no 

 yolk-sack was observed. 



Non-deciduate placenta. The remaining Mammalia are characterized 

 by a non-deciduate placenta ; or at least by a placenta in which only parts of 

 the maternal epithelium and no vascular maternal structures are carried away 

 at parturition. The non-deciduate placentae are divided into two groups : 

 (1) The polycotyledonary placenta, characteristic of the true Ruminautia 

 (Cervida?, Antilopicla?, Bovidse, Camelopardalidfe) ; (2) the diffused placenta 

 found in the other iion-decicluate Mammalia, viz. the Perissodactyla, the 

 Suidse, the Hippopotamida?, the Tylopoda, the Tragulich^, the.Sirenia, the 

 Cetacea, Manis amongst the Edentata, and the Leniurida?. The polycoty- 

 ledonai-y form is the most differentiated; and is probably a modification of 

 the diffused form. The diffused non-deciduate placenta is very easily 



