82 F. W. THYNG 



Iliac arteries. Each common iliac artery {Aa.il.com.) arises 

 from the lateral wall of the aorta directly opposite the third lum- 

 bar pair of dorsal intersegmental arteries, and on a level with the 

 2nd lumbar nerves. At first of small caliber the common iliacs 

 soon increase notably in diameter. The right common iliac 

 artery is the more fully displayed in the reconstruction (plate 1). 

 It extends laterally and caudad, passing ventral to the caudal 

 segment of the inferior vena cava, medial to the metanephros, 

 and dorsal to the ureter and Wolffian body (compare plate 2). 

 This relation of the common iliac artery, which is preserved in 

 the adult, is probably that of a dorsal intersegmental artery. 



The right common iliac artery terminates in two branches, the 

 external iliac {A.il.ext.), a medium sized artery which accom- 

 panies the corresponding vein, and the arteria hypogastrica 

 {A.hypogas.). 



The external iliac artery first extends laterally and gives off 

 a branch directed cephalad, the inferior epigastric (not shown in 

 the reconstruction). It then continues caudad in the proximal 

 part of the posterior limb-bud to finally join the A. ischiadica. 



The hypogastric artery is only a short trunk which divides, 

 lateral to the ureter, into dorsal and ventral branches (the so- 

 called anterior and posterior divisions of adult anatomy). The 

 dorsal branch appears in the drawing only as a short stump, but 

 probably here continues as the superior gluteal artery. The ven- 

 tral branch soon divides into the large umbilical artery (A.um.d.) 

 and a short trunk common to the sciatic and internal pudendal 

 arteries {A.isch.d. axid A.pud.i.). The umbilical artery extends 

 ventrally in the lateral body wall across the lateral side of the 

 anlage of the bladder into the caudal wall of the umbilical cord. 



The sciatic (inferior gluteal and A. comitans n. ischiadica) is 

 at first dorso-lateral to the corresponding vein {V.isch., plate 4) 

 with which it continues into the posterior limb-bud. The tap 

 between it and the femoral has already occurred. 



The internal pudendal is at first ventral to the sciatic vein but 

 soon bends ventrally into the cephalo-lateral part of the genital 

 papilla where it becomes the artery of the clitoris or penis, accord- 

 ing to sex. 



