THORAX AND ABDOMEN OF THE HORSE 151 



With the exception of the two last named, all these veins are 

 satellites of the corresponding arteries. The hepatic veins are 

 numerous and of various sizes. They join the vena cava as it lies 

 in the fossa provided for it by the liver. The phrenic veins are 

 of great size, generally two but possibly three in number, and enter 

 the vena cava as it is passing through the diaphragm. 



V. ILIACA EXTERNA. — The external iliac vein differs from the 

 homonymous artery in that it does not, as a rule, receive the deep 

 circumflex iliac vein ; and it does receive blood from the obturator 

 vein. 



V. ILIACA COMMUNIS. — This short, wide vein lies between the 

 external iliac and hypogastric arteries, and is formed by the union 

 of the external iliac and hypogastric veins. The sixth lumbar and 

 the ilio-lumbar veins join it, as does also the deep circumflex iliac 

 vein in those cases where it is not connected with the caudal vena 

 cava itself. 



CiSTERNA CHYLi.i — This elongated, thin-walled cistern lies to the 

 right of and slightly dorsal to the aorta, and between this vessel and 

 the right crus of the diaphragm, at the level of the first and second 

 lumbar vertebrae. Into the cistern open four or five large lymphatic 

 trunks, along which flows the lymph collected from the pelvic limb, 

 the pelvis, the abdominal wall and the abdominal viscera. Two 

 lumbar trunks (trunci lumbales) carry lymph from the lumbar lymph 

 glands, and two or three intestinal trunks (trunci intestinales) are 

 formed by the efferents from the gastric, hepatic, splenic and mesen- 

 teric glands. 



The thoracic duct (ductus thoracisus) leaves the cranial end of 

 the cistern and enters the thorax by following the right border of the 

 aorta. 



V. AZYGOS. — The commencement of the vena azygos ^ must also be 

 soucrht to the right of the aorta, not far from the hiatus aorticus of the 

 diaphragm. The vein is formed by the union of the first lumbar vein 

 of the right side and vessels bringing blood from the psoas and trans- 

 verse abdominal muscles and the crura of the diaphragm. The azygos 

 vein accompanies the thoracic duct into the thorax. 



The ILIAC FASCIA (fascia iliaca). — Preparatory to the dissection of 

 the lumbar musculature, an examination must be made of the iliac 

 fascia. This is a stout sheet interposed between the peritoneum and 



' xv\6s (chylos) [Gr.], juice. 

 2 a (priv.)-|-fin"5j (zygos) [Gr.], a yoke. Unpaired. 



