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 



Section of human uterus and attached placenta at :$oth week of gestation, ccxi.vi". 



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

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

 583 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- 

 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 chajmel termed the 

 ' circular sinus \ 



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

 niagn. ccxlvi". 



