56 STRUCTURE AND CLASSIFICATION OF BIRDS 



are several veins which extend on to the pectoral and even 

 on to the abdominal region of the body. Most important 

 on physiological grounds of these is the abdomino-pectoral, 

 which on each side of the body collects blood from the 

 pectoral and abdominal regions, and forms in the female 

 during the breeding season a network of vessels with the 

 corresponding arteries. 



The vena cava inferior is composed of the two hepatic 

 trunks and of an unpaired median portion, the main stein of 

 the vena cava. The latter traverses the right lobe of the 

 liver, and in its transit receives several smaller twigs from 

 the liver. At the commencement of the kidney the vena 

 cava divides into, or rather is composed of, the two venae 

 iliacae. It has been pointed out that in diving birds the 

 part of the vena cava which traverses the liver is wider than 

 in other birds, a state of affairs which is paralleled in certain 

 aquatic mammals. 



The two common iliacs divide each of them into two veins, 

 of which the first to be given off is termed the vena iliaca 

 externa. This divides at once in the pigeon (according to 

 JOURDAN) into the femoral and into a trunk which runs 

 along the kidney, and after giving off the sciatic and 

 numerous branches to the kidney substance receives the 

 hypogastric from the pelvic region, and then joins its fellow 

 in the middle line ; at the point of junction of the two 

 iliacae externae a median coccygeal is received, and a median 

 mesenteric from in front. The other branch of the iliaca 

 communis is purely renal. It results from what has been 

 said that blood entering the kidney from any of the 

 branches of the common iliacs may traverse the kidney 

 substance before reaching the heart via the vena cava 

 posterior. The suprarenal bodies also have their portal 

 system. The body of each side receives a branch from the 

 rib region and from the branch of the iliac which runs 

 embedded in the substance of the kidney. 



The existence of a renal portal system in birds is 

 therefore possible, but not certain, on the anatomical facts 

 available ; but the liver portal system, as in all other verte- 



