. IX. 



THE STRUCTURE OF THE HUMAN PLACENTA, 



I. OF THE STRUCTUKE OF THE TUFTS AND VILLI OF THE 



PLACENTA. 



1. Of the Configuration of the Tufts. 



A placental tuft resembles a tree. It consists of a trunk, of 

 primary 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. 



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

 the tuft are covered by a very fine transparent membrane, appa- 



