THE DEVELOPMENT OF THE VASCULAR SYSTEM. 



249 



cceliac artery arises from the ventral side of the aorta a short distance cranially 

 to the omphalomesenteric (Fig. 226) and gives rise in turn to the gastric, hepatic 

 and splenic arteries. The inferior mesenteric artery also arises from the ventral 

 side of the aorta some distance caudal to the omphalomesenteric (Fig. 226). 

 In the early stages these visceral arteries arise relatively much farther cranially 

 than in the adult. During development they gradually migrate caudally to 

 their normal positions. 



Int. mammary arter 



Inf. epigastric artery 



Umbilical artery 



', - Vertebral artery 



-- Aorta 



-* Intercostal artery 



Femoral artery 



FIG. 225. Diagram of human embryo of 13 mm., showing the mode of development 

 of the internal mammary and inferior epigastric arteries. Mall. 



Other branches of the aorta develop in connection with the urinary and 

 genital organs, and, with the possible exception of the renal arteries, they are 

 primarily segmental in character. Several branches supply the mesonephroi, 

 but when the latter atrophy and disappear the vessels also disappear. The 

 renal arteries do not develop until the kidneys have practically reached their 

 final position in the embryo, and then they arise directly from the aorta. Dur- 

 ing the development of the genital glands several pairs of branches from the 

 aorta supply them with blood. Later the majority of these vessels disappear, 

 one pair only persisting as the internal spermatic arteries which differ in accord- 

 ance with the sex of the individual. In both sexes they are at first very short; 



