172 EQUINE ANATOMY. 



do not always rise from the abdominal aorta, but more 

 commonly from the external iliac. 



Veins. — Posterior vena cava. — Beginning at the 

 pelvis by the pelvic crural trunks (see page 182) placed 

 under the bodies of the lumbar vertebrae, reaches the 

 superior border of the liver, passes through the phren- 

 ic portion of the diaphragm to the posterior and ex- 

 ternal part of the right auricle of the heart, being 

 thus divided into a sub-lumbar, hepatic and thoracic 

 portions. The numerous collateral afferents are : the 

 diajDhragmatic, the vena portse, the renal, the sperma- 

 tic and several lumbar veins. The vena portse does 

 not empty directly into the vena cava, but indirectly 

 by the supra hepatic veins, which rise from its subdi- 

 vision, the subhepatic veins. It is constituted by three 

 principal roots : the great and small mesenteric and 

 splenic veins; it receives as collateral affluents the 

 right gastro-epiploic and the anterior gastric veins. 



Lymphatics. — 1. Those of the rectum and floating 

 colon are placed at the base of the tail on each side 

 of the spliincter, also along the small cui'vature of the 

 rectum and between the folds of the mesentery. 

 Their efferent branches unite to the divisions of the 

 sublumbar ganglions. 



2. Those of the folded colon form a double chain 

 on the tract of the colic arteries. Their branches 



