100 ON THE PLACENTAL STRUCTURES OF THE TENREC 



ciduous serotina is ordinarily separable from the uterine surface of 

 the placenta in a coherent sheet, whilst in the surface of the 

 placenta, besides other maternal elements, there are the processes 

 known as ' Decidua-Fortsatze ' mixed up inextricably like them, but, 

 unlike them, distinguishable by the naked eye. 



The Insectivora have the umbilical vessels confined to the pla- 

 centa, but their ultimate capillaries are apposed to similar maternal 

 vessels not immersed in maternal sinuses. Their decidua reflexa is 

 more or less incomplete. The placental site may be anywhere in 

 the circumference of the uterine tube. The tenrec's maternal and 

 foetal structures are exceedingly aberrant. The upgrowth of the 

 chorion, the absence of any envelope exteriorly to the amnios, and 

 the distinction of the utero-placental region into two areae, clothed 

 with distinct kinds of mucous tissue, are unique points in this 

 animal. By its amniotic corpuscles it resembles the elephant 

 among deciduate, and several orders among the non-deciduate 

 mammals. 



In the Rodent placenta the ramifications of the umbilical vessels 

 have the same relations as in the Insectivora ; but the chorion is 

 supplied with blood-vessels from the omphalo-mesenteric system in 

 its non-placental parts, which consequently take a share in the 

 nourishment and respiration of the foetus. The decidua reflexa is, 

 when not rudimentary from the beginning, fragmentary at the end 

 of gestation. The deciduous serotina is always distinct from the 

 placenta, and separable from it (even when not separated) at par- 

 turition. The placentae are always attached to the mesometrial 

 border of the uterine cornu. 



In the Camivora the umbilical ramifications spread over the 

 entire chorion, not merely in its placental zone, absorbing nutri- 

 ment consequently from, and interchanging products with, the 

 secretions of the non-placental uterine mucous membrane. The 

 allantois is here always a perfect sac, separating the exterior of the 

 amnios from the interior surface of the chorion. They have no 

 decidua reflexa properly so called. The omphalo-mesenteric vessel 

 are to be found persistent within the cavity of the abdomen, as in 

 the Rodents, for some time after birth; but they never reach the 

 chorion, as in that class. There is an approximation made, by 

 the colossal maternal capillaries of certain of this class, to the sinus- 

 system of the Simiaclae. 



