THE UMBILICAL CORD. 



53 



on the other. Maternal capillaries are wanting- within the placenta, since they have 

 become early replaced by the intervillous lacunae. The maternal blood is carried 

 away from these spaces by wide venous channels which pass directly from the lacunae 

 through the placental septa into the basal plate, where they form net-works from which 

 proceed the larger venous trunks. At the edge of the placenta the anastomosing cav- 

 ernous spaces form an annular series of intercommunicating venous channels known 

 collectively as the marginal sinus, into which empty numerous placental veins, on the 

 one hand, and from which, on the other, pass, tributaries to the larger veins of the 

 uterus. 



Fig. 62. 



Umbilical vein 



Umbilical arteries 



Corrosion preparation of human placenta, showing general grouping of fcetal vessels into lobules. 



The Umbilical Cord. — -The umbilical cord, or fiiriiaihis umbilicalis, which 

 connects the body of the foetus with the placenta, thereby conveying the foetal blood 

 to and from the respiratory and nutriti\'e apparatus, is formed in consequence 

 of the fusion of three originally distinct structures, — the belly-stalk, the vitelline 

 stalk, and the amnion. The first of these, in addition to forming .the early attach- 

 ment of the foetus to the chorion, supports the rudimentary allantoic canal and the 

 allantoic, later umbilical, blood-vessels. The vitelline stalk encloses the diminish- 

 ing vitelline duct and the remains of the vitelline blood-vessels, while surrounding 

 these stalks the amniotic sheath gradually becomes more closely applied. These 



