STRUCTURE OF HUMAN PLAf'ENTA. 445 



XXTX.— THE STRUCTURE OE THE IIUiMAN 

 PLACENTA.— (Plates V. VI.) 



I. — OF THE structure of the tufts and villi of the 



PLACENTA. 



1. — OJ the Conjujvratiaii of tlic Tufts. 



A PLACENTAL tuft resembles a tree. It consists of a tniuk, 

 of primaiy branches, and of secondary branches or terminal 

 villi, which are attached as solitary villi to the sides of the 

 primary branches, and to the extremities of the latter, in which 

 case they generally present a digitated arrangement. The 

 villus, when solitary, is cylindrical, or slightly flattened, or 

 somewhat club-shaped ; when digitated, each division may be 

 much flattened, or is then generally heart-shaped. The 

 digitated villi are only solitary villi grouped together at the 

 extremity of a primary branch. 



2. — Of the External Membrane of the Tufts. 



Tlie trunk, the primary branches, and the terminal villi of 

 the tuft are covered by a very fine transparent membrane, 

 apparently devoid of any structure. Tliis membrane may be 

 described as bounding the whole tuft, passing from the trunk 

 to the branches, and from these to the villi, the free extremities 

 of which it closely covers. Its free surface is smooth and 

 glistening — its attached surface is somewhat rough.* 



* Professor RciJ, "On the Anatomical Hdutions of the Bloodvessels of the 

 Mother to those of the Foetus in the Humun Species." — Eil. Med. Surg. Journal, 

 1841, iMge 7. 



