XI VEINS 525 



in the ventral abdominal wall. Small lumbar arteries 

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

 abdomen. 



The pulmonary artery (p. a) 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 arteriosm, with the 

 aorta : this is the solid vestige of the embryonic connec- 

 tion between the fourth arterial arch and the aorta 

 (compare p. 452, and Fig. 120). 



Each precaval (1. pr. c, r. pr. c) receives a subclavian 

 (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 (i. cs) and the anterior surface of the 

 diaphragm (a. ph) ; and a small internal jugular (i. ju) 

 from the brain, opening into the corresponding external 

 jugular nearly opposite the subclavian. 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 Mo-lumbar 

 veins (i. 1) from the body-walls : the left ilio-lumbar 



