No. 3.] A HUMAN EMBRYO TWENTY-SIX DAYS OLD. 473 



the cardinal extends along the whole length of the Wolffian body, 

 receiving the blood from this organ. The omphalo-mesenteric 

 receives a vein from the mesentery, — the inferior mesenteric. 

 The jugular and cardinal unite to form the ductus Cuvieri, 

 which on the right side passes directly into the sinus reuniens, 

 while on the left it flows across the dorsal side of the heart 

 before it empties into the same. 



On either side there are several large veins which arise in 

 the anterior extremity, soon unite to form a single branch and 

 empty into the ductus Cuvieri. On the left side these veins 

 form a sinus around the united branch from the fourth and fifth 

 cervical nerves, and then communicate with the cardinal vein 

 as well as with the ductus Cuvieri. 



It is the left omphalo-mesenteric vein which remains in the 

 specimen. The vein passes around the dorsal side of the ali- 

 mentary canal, and about in the middle of the liver unites with 

 the umbilical vein. The united veins now become greatly 

 narrowed and then again enlarge to form the sinus reuniens. 

 From the distal side of the constriction the veins pass to the 

 substance of the liver, while on the proximal side these efferent 

 branches enter, forming a portal system. 



Ccelom. 



A cast of the ccelomic cavity is shown in Fig. 2, PI. XXIX. 

 The picture was taken from the inverted model viewed from the 

 dorsal and left sides. The slit along the dorsal side marks the 

 mesentery while the grooves on either side of this indicate 

 the position of the Wolffian bodies. The bulbous end of this 

 model represents the pericardial cavity. 



The pericardial cavity surrounds the whole heart, as shown 

 in the sagittal section in Fig. 2, PI. XXX. The cavity is per- 

 forated only where the large veins enter, and where the artery 

 leaves the heart. The cavity completely surrounds the bulbus 

 aortae to its origin in the ventricle, the ventral side of this cav- 

 ity being directly continuous with the ventral pericardial cavity. 

 On the dorsal side the cavity is broken through for the trans- 

 mission of the veins to the heart. Between the bulbus and the 

 entrance of these veins the cavity extends across this median 

 line as three distinct openings. On the dorsal side of the heart 



