330 IVAN E. WALLIN 



and to which Mall ('12) ascribes the source of the intima may 

 be seen in connection with the endocardium in its entire length. 



The blood vessels are collapsed in places so that it is not pos- 

 sible to trace them in their entire extent. The communication 

 between the first pair of aortic arches and the dorsal aortae 

 could not be seen. The dorsal aortae are distinct throughout 

 their course lying dorsal to the gut tube. There is no indication 

 of a second pair of aortic arches. The first pair come off at a 

 point cephalad to the first mesodermal somites. Vitelline ves- 

 sels containing blood are easily discernible in the wall of the 

 yolk sac and yolk stalk. Vitelline veins run dorsally in the 

 cephalic part of the yolk stalk to gain the caudo-ventral aspect 

 of the sinus venosus opposite the fourth pair of somites. The 

 allantoic veins (fig. 4) begin in the belly stalk as a single trunk 

 or sinus. As the sinus approaches the body of the embryo it 

 bifurcates to fonn the two allantoic veins which diverge and 

 run laterally and cephalad to gain the lateral lips of the coelom. 

 In this -position they run in a cephalad direction to the septum 

 transversum where they enter the caudo-dorsal part of the sinus 

 venosus. The allantoic arteries leave the dorsal aortae at a point 

 opposite the place where the allantois is evaginated from the 

 hind-gut and caudal to the last pair of somites. The arteries 

 run ventrally on either side of the allantois in the belly stalk. 

 At a point more distal than the bifurcation of the allantoic ve- 

 nous trunk the allantoic arteries anastomose to form a single 

 trunk. I have been unable to find any trace of the anterior and 

 posterior cardinal veins. At the cephalo-dorsal aspect of the 

 sinus venosus on the left side there is a short bud-like diverticu- 

 lum which may represent the future ductus Cuvieri. 



I wish to take this opportunity to thank Dr. Boencke for this 

 valuable embryo and Profs. H. D. Senior and F. W. Thyng for 

 assistance and advice in connection with this piece of work. 



