Frederic T. Lewis 



233 



ment of the veins have been illustrated by reconstructiou after the 

 method of His. The drawings are similarly enlarged and arranged in 

 Plates I and II. Each jDair of figures represents a single embryo, split 

 in the median plane and laid open, the left half of the embryo lying 

 on the right-hand page, and vice versa. All the blood-vessels involved 

 have been drawn except the median aorta and its median (mesenteric 

 and gastric) branches. Every drawing shows two sets of arteries: 1st, 

 a regularly arranged series of intersegmental arteries, A. I., and 3nd, 

 the irregularly disposed arteries running laterally from aorta to the 



V.U.s 



-V.U.d. 



Fig. 7. Rabbit embryo of 6.6 mm., 13 clays, 12 hours. Series 460, section 117. 

 X 4.5. Tliis section should have been reversed to be in the conventional position. 

 The right side is here drawn at the rii,'-ht of the observer. 



glomeruli of the Wolffian body. These may be named the mesonephric 

 arteries, A. M.: their position in relation to the veins makes them a 

 most important landmark. The umbilical arteries, A. IT., are also indi- 

 cated. All the arteries are shown as cut across at the position where 

 they leave the aorta. 



Figs. 1 and 2, Plate I, picture the condition already described. In 

 this 7.0 mm. embryo the posterior cardinal veins, V. C., pass cephalad 

 ■to join the anterior cardinals, and then to turn back at a sharp angle 

 and enter the heart. A^entral to the posterior cardinal vein is seen the 

 line of mesonephric arteries, and ventral to these is an anastomosis of 

 cardinal tributaries. This anastomosis forms a new vessel coming from 



