750 



ANATOMY OF VERTEBRATES. 



to accompany the arteries along the centre of the villi, emerge 

 from the substance of the placenta, about sixteen in number, 



582 



ch 



Of, 



f>83 



Section of human UUTUS ;nid attached placenta at :tOth week of gestation. CCXLVI". 



with a less tortuous course than the arteries, converging to the 

 root of the funis and ultimately uniting to form a single umbilical 



vein. After the sixth month 

 the capillaries of the villi 

 begin to disappear. The 

 uterine arteries, fig. 582, a, 

 about the size of a crow-quill 

 in the later months, have a 

 tortuous or curly course, and 

 they ultimately pour their 

 blood into the large venous 

 sinuses, ib. us. These are 

 most numerous upon the in- 

 ner side of the decidua con- 

 stituting the uterine sur- 



o 



face of the placenta, pass- 

 ing obliquely through that 

 layer into the uterine wall; 

 some extend into the decid- 



ual septa, and some lead to the marginal channel termed the 



' circular sinus '. 



Villi of tuft of foetal part of placenta, at six months; 



Ci'Xi.vi". 



