xi VEINS 525 



arteries are also given off from the aorta to the walls of the 

 abdomen. 



The pulmonary artery (p.d) divides soon after its origin 

 from the right ventricle into two branches, one supply- 

 ing each lung. Just before its bifurcation it is connected 

 by a short cord, known as the ductus arteriosus, with the 

 aorta : this is the solid vestige of the embryonic connection 

 between the fourth arterial arch and the aorta (compare p. 

 452, and Fig. 120). 



Each precaval (I. pr. c, r. pr. c) receives a sub- 

 clavian (s. d. v) from the fore-limb ; an external jugular 

 (e. ju) from the head, running along the neck just 

 beneath the skin ; a small anterior epigastric from the 

 ventral thoracic wall, as well as small vessels from some 

 of the anterior intercostal spaces (/. cs) and the anterior 

 surface of the diaphragm (a. ph) and a small internal 

 jugular (i. ju) from the brain, opening into the cor- 

 responding external jugular nearly opposite the sub- 

 clavian. An azygos vein (az. v\ representing part of the right 

 cardinal of the embryo (compare p. 456) and receiving blood 

 from the posterior intercostal spaces, also opens into the 

 base of the right precaval. 



There is no renal portal system, as in the dogfish and frog 

 (pp 454 and 85). A pair of internal iliac veins (i. il. v) in the 

 pelvic cavity unite to join a median vessel (c. il. v\ the 

 hinder end of the postcaval, which receives on either side 

 an external iliac (e. il. v) : this is constituted by a femoral 

 vein (fm. v) from the hind-limb ; a, posterior epigastric (p.epg\ 

 from the ventral walls of the abdomen, entering the femoral 

 just external to Poupart's ligament ; and by small veins from 

 the bladder as well as from the uterus in the female. 

 Slightly in front of the external iliacs the postcaval receives 

 a pair of large ilio-lumbar veins (i. I) from the body-walls : 



