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TEXT-BOOK OF EMBRYOLOGY. 



in the female, as the ovaries move farther into the pelvic region, they become 

 considerably elongated to form the ovarian arteries; in the male, with the 

 descent of the testes, they become very much elongated to form the testicular 

 arteries. 



The fourth (or fifth ?) pair of segmental lumbar arteries primarily gives 

 rise to the vessels which supply the lower extremities, viz., the iliac arteries. 

 These then would be serially homologous to the subclavians. But certain 

 changes occur in this region, which are due to the relations of the um- 

 bilical arteries. The latter, as has already been noted, arise as paired 

 branches of the aorta in the lumbar region, pass ventrally through the genital 

 cord (Chap. XV) and then follow the allantois (urachus) to the umbilical cord. 



Coeliac artery 



Sup. mesenteric 

 (vitelline) artery 



Umbilical artery 



Aorta 



Duodenum 



Inf. mesenteric artery 

 Int. iliac artery 



FIG. 226. Diagram of the visceral arteries in a human embryo of 12.5 mm. Tandler. 

 Numerals indicate segmental arteries. 



During foetal life they carry all the blood that passes to the placenta. At an 

 early period a branch from each iliac artery anastomoses with the corresponding 

 umbilical, and the portion of the umbilical artery between the aorta and the 

 anastomosis then disappears. This makes the umbilical artery a branch of 

 the iliac; and the blood then passes from the aorta into the proximal part of 

 the iliac which becomes the common iliac artery of the adult. At birth, when the 

 umbilical cord is cut, the umbilical arteries no longer carry blood to the placenta, 

 and' their intraembryonic portions, often called the hypo gastric arteries, persist 

 only in part; their proximal ends persist as the superior vesical arteries, while 

 the portions which accompanied the urachus degenerate to form the lateral 

 umbilical ligaments. 



