170 THE THIRD DAY. [CHAP 



Small arteries to various parts of the body are now 

 being given off by the aorta and its branches. The 

 capillaries in which these end are gathered into veins 

 which unite to form two main trunks on either side, the 

 cardinal veins, anterior and posterior (Fig. 36, Fig. 58 



Fig. 58. 



Diagram of the Venous Circulation on the 

 Third Day. 



n. Heart. J. Jugular or anterior cardinal vein. C. Inferior 

 or posterior cardinal vein. Of. Vitelline vein. dc. Ductus 

 Cuvieri. 



J" and 0), which run parallel to the long axis of the body 

 in the upper part of the mesoblast, a little external to 

 the mesoblastic somites. These veins, which do not 

 attain to any great importance till well on in the third 

 day, unite opposite to the heart, on each side, into a 

 short common trunk at right angles to themselves. 

 The two short trunks thus formed, which bear the 

 name of ductus Cuvieri (Fig. 36, Fig. 58, dc), running 

 ventralwards and then transversely straight inwards 

 towards the middle line fall into the sinus venosus. 



The two ductus Cuvieri pass from the heart to the 

 body walls in a special horizontal mesentery, whose for- 

 mation and function we shall return to in speaking of 

 the formation of the pericardial cavity. The position of 

 one of them is shewn in section in Fig. 59 B, dc. 



