124 THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



scending aortae, others from the dorsal aorta. From the seventh pair, 

 which arise just where the descending aortae fuse, the subclavian arteries 

 pass off to the upper limb buds and the vertebral arteries to the head. The 

 latter are formed by a longitudinal anastomosis between the first seven 

 pairs of intersegmental arteries on each side, after which the stems of the 

 first six pairs atrophy. 



FIG. 126 A. Reconstruction of a 12 mm. pig embryo, to show the veins and heart from the 

 left side. For names of parts see Fig. 126 B on opposite page (F. T. Lewis). X 9. 



Ventro-lateral arteries from the dorsal aorta supply the mesonephros 

 and genital ridge (Fig. 123). Ventral arteries form the cceliac artery to 

 the stomach region, the vitelline, or superior mesenteric artery, to the 

 small intestine, and the inferior mesenteric artery to the large intestine. 



The umbilical arteries now arise laterally from secondary trunks 

 which persist as the common iliac arteries. 



