648 SIR WM. TURNER ON THE PLACENTATION OF HALICORE DUGONG. 



chorion, considerably nearer to the left than the right pole, so that it was excentric in 

 position (fig. 2). The greatest breadth of the zone was on the anterior convexity of the 

 chorion, where it measured 11^ inches (292 mm.); in the concavity it was only about half 

 that breadth, whilst at a line about midway between it was 9^ inches (241 mm.). In the 

 concavity of the chorion, the zone was thicker and folded, whilst on the convexity it was 

 thinner and smoother, but the whole surface was flocculent from the presence of multitudes 

 of closely compacted villi. The margins of the zone were differentiated from the non- 

 villous chorion by a sharp sinuous line. The left border was about one foot from the 

 left pole of the chorion, whilst the right border was about 2-^ feet from the right pole,* 

 so that if the chorion be supposed to be equally divided into a right and a left half, the 

 whole of the zone was situated in the left half. The chorionic zone formed the foetal 

 part of the placenta, and it was found to be detached from the maternal placenta, when 

 the uterus was opened, as has already been stated. 



I then lifted out of the gravid horn the chorion with its contents, and made a cut 

 through that membrane opposite to the spinal column of the foetus from the cephalic 

 pole to the right border of the placental zone. A large sac was opened into, which proved 

 to be the allantois. This sac was very capacious, and completely surrounded the amnion 

 from its cephalic pole to the right placental border of the chorion. The outer wall of the 

 sac, smooth, and free on its inner surface, was formed by that part of the allantois which 

 constituted the endochorion, and which extended from the cephalic pole of the chorion 

 to the right border of the placenta. The inner wall of the sac consisted of the allantois 

 which enveloped the bag of the amnion. Immediately subjacent to the right margin of 

 the placenta, where it was opposite the back and in part the sides of the foetus, the 

 endochorion was reflected on to the outer surface of the amnion, and became continuous 

 with the allantois covering that membrane. The sac of the allantois was consequently 

 not continued over the inner surface of the placenta in its whole extent, for throughout 

 an ovoid area 8 inches in diameter in one direction, and 5 inches in another, which lay 

 opposite the back and sides of the foetus, the amnion was in direct contact with the 

 inner surface of the placenta. The arrangement of the allantois in relation to the 

 part of the placenta which was opposite the belly of the foetus differed materially from 

 that above described, for it was prolonged across the inner surface of that portion of the 

 placenta from the right to the left border, and its sac was continued into the caudal part 

 of the chorion up to the caudal pole. Immediately to the left of the ovoid area, where 

 the amnion was in direct contact with the placenta, the allantoic sac was again inter- 

 posed between the placental area of the chorion and the amnion, and was continued into 

 the caudal pole of the chorion so as to surround the caudal end of the amnion, as com- 

 pletely as its cephalic end. Hence the whole extent of the amnion from the caudal to 

 the cephalic end of the foetus, with the exception of the ovoid area in relation to a 

 limited part of the inner surface of the placenta, was surrounded by and in contact 



* Owing to the poles of the chorion being rounded and bent each on itself, it is difficult to fix with precision the 

 central point of the pole. The above measurements are therefore to be regarded as approximative. 



