DEVELOPMENT OF THE CIRCULATORY SYSTEM. 



225 



the rest; the part so cut off forms the pericardium (Fig. 201). 

 Thus the ducts of Cuvier are instrumental in separating the 

 pericardial from the pleural cavity. If the primitive pleuro- 

 pericardial communication (iter venosum of Lockwood) persists 

 between them, it occurs as a foramen in the pericardium behind 

 the part of the superior vena cava derived from the duct of Cuvier. 

 2. The Vestigial Fold and Oblique Vein of Marshall. — In the 

 human embryo during the 3rd week and for some weeks after- 

 wards there is a right and left duct of Cuvier and corresponding 

 cardinal veins (Fig. 185). A left superior vena cava is present 

 and may persist. The vestigial fold and oblique vein of Marshall 

 (Fig. 184) are all that usually remain of the left superior vena 



rt.d. 

 of Guuier- 



sub. clau. 

 -""< sub. clau.. 



,„i\0";'--- ] \ (left sup. intercost. 

 If! (left jug.) 



left sup. intercost. 

 " (left card.) I 



pericard — -r 



[_left duct of Cuvier V 

 -fold of Marshall i 

 -pericardium 



-left horn, sinus uenosus 

 ' Eustach. value 



Kft.?£ 



inno"!;-. 



p. aur. 



■ sub. clau. 



-left. jug. 



, (> ) jjlpericard. 

 ^Jsin.uen.JpUeft d.Cuuier 

 ^tV-left. card. 



Fig. 1S5. 



Fig. 184. 

 Fig. 184.— The Remnants of the Left Superior Vena Cava, derived from the Structures 



shown in Fig. 185. 

 Fig. 185.-Diagram of the Sinus Venosus and Duets of Cuvier of the human embryo 



about the 3rd week. 



cava. The right superior vena cava within the pericardium 

 passes in front of the right pulmonary vessels, and is bound to 

 them by a mesentery or fold of serous pericardium ; the left has 

 a similar relationship (Fig. 184); when it disappears this fold 

 remains in front of the left pulmonary vessels as the vestigial 

 fold. The intra-pericardial part of the left vena cava or duct of 

 Cuvier becomes the oblique vein (Fig. 184): it turns round the 



