THE HUMAN PLACENTA. 361 



variable and is easily seen to be related to the distribution of the vessels. The 

 insertion may even be entirely outside the placenta, which yet may otherwise 

 be normally developed. Such insertions are called velamentous. The usual 

 type is shown in figure 240. The arteries come down together from the cord; 

 they usually, but not always, anastomose by a short transverse vessel, which 

 lies about half an inch above the surface of the placenta; it could not be shown 



FIG. 240. HUMAN PLACENTA AT FULL TERM, DOUBLY INJECTED TO SHOW THE SUPERFICIAL DISTRIBUTION OF 



THE BLOOD-VESSELS. 

 The veins are drawn dark and lie deeper than the arteries. One half natural size. 



in the figure. Very rarely, if ever, are there any arterial or venous anastomoses 

 on the surface of the placenta. The arteries there spread out in a manner which 

 may be described as roughly symmetrical. The veins partially follow the course 

 of the arteries. When the cord is inserted near the margin the symmetry of the 

 placental vessels is greater, when the insertion is near the center the symmetry is 

 less, than in the figure. 



