356 The Vena Cava Inferior 



in the vena cava ; the corresponding vessels of the left side pass into 

 the left renal vein. 



The ovarian veins communicate freely with the uterine veins in the 

 broad ligament ; they end like the spermatic veins. 



The renal veins begin at the hilum of the kidney and pass inwards 

 in front of the renal artery. The left vein is the longer ; it crosses in 

 front of the aorta, and receives the inferior phrenic, supra-renal, and 

 the spermatic or ovarian of the left side. 



The hepatic veins return to the vena cava, by three or four large 

 trunks, the blood which was brought to the liver by the portal vein 

 and the hepatic artery. They enter the vena cava where it lies in 

 the notch at the back of the liver, between the layers of the coronary 

 ligament, and close below the diaphragm. 



The descent of the diaphragm in inspiration, and especially so 

 during active exercise, compresses the liver and gently squeezes the 

 blood from its sluggish veins. (For portal system see p. 337.) 



THE LUMBAR NERVES 



The lumbar nerves break, like the other spinal nerves, into an 

 anterior and a posterior division ; the posterior passes between the 

 transverse processes and gives off an internal and an external branch. 

 The internal branch is small, and ends in the erector spinas ; the 

 external branch also supplies the erector, but the three upper branches 

 give, in addition, cutaneous twigs for the loin and buttock* 



The lumbar plexus is formed by a descending (dorsi-lumbar) 

 branch from the twelfth dorsal nerve, and by the anterior divisions of 

 the first, second, and third lumbar nerves, and by most of that of the 

 fourth. It is lodged in the hinder part of the psoas, and is thus 

 anterior to the quadratus lumborum. The root-fibres for its nerve s 

 emerge from the lumbar enlargement of the cord. 



In addition to a communicating twig to the second, the anterior 

 division of the first lumbar nerve gives off the ilio-hypogastric and 

 illo -inguinal branches, both of which pass outwards below the anterior 

 division of the last dorsal nerve, in front of the quadratus lumborum, 

 and then through the transversalis and into the interval between that 

 muscle and the internal oblique. 



The ilio-hypogastric gives a branch through the oblique muscles 

 which passes over the iliac crest, to the skin of the buttock, and 

 another through the oblique muscles to the skin in the hypogastric 

 region. 



The ilio-inguinal escapes through the external abdominal ring and 

 splits into a branch for scrotum or labium, and one for the skin over 

 the upper and inner part of Scarpa's triangle. In their course the 

 divisions of the first lumbar nerves supply the oblique muscles. 



The first lumbar nerve lies below the first lumbar vertebra, and in 



