AND THOSE OF CERTAIN OTHER MAMMALIA. 77 



i. Maternal and Foetal Structures developed in utero in 



CONNEXION WITH THE EMBRYOS. 



Owing to the state of preservation in which the specimen was 

 when it came into my hands, the maternal and foetal structures in 

 connexion with the chorion had, in every case but one, become 

 self-analysed into three parts. These parts were, first, an area of 

 tissue continuous at its periphery with the non-placental uterine 

 mucous membrane ; secondly, a lamina of membrane floating 

 loosely, and, like the utero-placental area, perforated centrally by 

 vascular orifices ; and, thirdly, the placenta proper of a diameter of 

 about half an inch. One ovum only retains its natural connexion 

 with the uterine wall ; but in several cases the lamina of mem- 

 brane ordinarily found floating loosely remains attached to its utero- 

 placental area. Of this area I will first speak. It is sub-circular, and 

 bounded by a slightly raised parapet of uterine mucous membrane, 

 with which an upgrowth of the chorion was continuous in all the 

 ova, and remains so in one instance at present. The diameter of 

 each utero-placental space thus bounded being about half an inch, 

 its area is divisible into two regions — one, the outer one, being 

 quoit-shaped and surrounding a circular central inner region. 

 The depth of the outer ring is about half the length of the 

 diameter of the entire area ; it is clothed with a mucous membrane 

 of pulpy appearance and corrugated more or less regularly. In 

 being thicker, and in being corrugated, this portion of the utero- 

 placental area contrasts with the mucous coating of non-placental 

 portions of the uterus, the mechanical pressure and contact of the 

 many foetuses accounting probably for the smoother and thinner 

 character of the mucous layer in the latter portions of the organ. 

 The central circular portion of each utero-placental area is dis- 

 tinguished, by its irregularly perforated and discoloured appear- 

 ance, both from the ring-shaped area immediately surrounding it 

 and from the rest of the uterine mucous coat. The membrane 

 covering both regions in each utero-placental area is single, and 

 does not admit of being split up into laminae ; but in several cases 

 the lamina, more commonly found floating freely, is left adhering to 

 the utero-placental area. This lamina, when free, presents many 

 orifices of blood-vessels, centrally ; and its general structure is loose 

 and pulpy. When adherent to the utero-placental area, it is by its 



