THE RABBIT 287 



this point it receives the following branches, all of them paired, 

 but the two members of a pair not always meeting the postcaval 

 in the same transverse plane: the large iliolumbar veins, which 

 join the postcaval vein a short distance in front of the external 

 iliacs, coming from the lumbar muscles; the spermatic veins (in 

 the male) or ovarian veins (in the female), which join the post- 

 caval a short distance in front of the iliolumbars and may be 

 traced to the scrotum or ovary, respectively, on each side; the 

 small lumbar veins, numbering seven pairs, which enter the dorsal 

 surface of the postcaval at regular intervals along its course pos- 

 terior to the diaphragm, coming from the muscles of the body 

 wall ; the large renal veins from the kidneys, the left renal being 

 posterior to the right renal in position (the left spermatic and 

 ovarian in some cases join the left renal vein) ; the adrenolumbar 

 veins, the right vein usually joining the postcaval immediately in 

 front of the right renal, and the left vein usually uniting with the 

 left renal ; the large hepatic veins, usually four in number, which 

 enter the postcaval just behind the diaphragm, bringing blood from 

 the liver ; and the phrenic veins, which meet the postcaval as it is 

 passing through the diaphragm, bringing blood from that organ. 



Exercise 12. Draw a diagram of the abdominal portion of the post- 

 caval vein and its branches, so far as observed. 



The Arteries. Two groups of arteries may be distinguished: 

 ( 1 ) the pulmonary arteries, which carry venous blood to the lungs ; 

 and (2) the aorta and its branches, which carry arterial blood to 

 the tissues. 



The aorta is the great artery which lies in the mid-dorsal line 

 of the body cavity and sends branches to all the various organs of 

 the body. It is composed of two portions, the thoracic aorta and 

 the abdominal aorta. 



The thoracic portion of the aorta will be studied later with the 

 organs of the thoracic cavity. The abdominal aorta lies just be- 

 neath the spinal column, in the abdominal cavity, and extends 

 from the diaphragm to the hinder end of the trunk, lying along- 

 side the postcaval vein throughout the greater part of its course ; 

 observe carefully its relation to this vein. Follow the aorta to 



