312 



AN INTRODUCTION TO ZOOLOGY 



previously been pointed out that the internal jugular vein leaves 



the cranial cavity through the 

 foramen lacerum posterius in 

 company with the ninth, tenth 

 and eleventh cranial nerves. 

 From this point it runs back 

 along the side of the trachea 

 to enter the external jugular 

 vein just before this joins the 

 sub-clavian, and the trunk 

 formed by the union of these 

 two vessels is sometimes 

 designated the common jugu- 

 lar vein. 



The leit pre-caval 

 vein (vena cava anterior 

 sinistra) 'is constituted in a 

 similar way to the right, 

 with the one important ex- 

 ception that it receives no 

 azygos vein. After its for- 

 mation in front of the first 

 rib it enters the thoracic 

 cavity, passes back along the 

 inner side of the left lung and 

 crosses between the heart and 

 the root of the left lung to 

 enter the left dorsal wall of 

 the right atrium. 



The post-caval vein 

 (vena cava posterior) is a large 

 trunk formed at the posterior 

 end of the abdominal cavity 

 by the union of the two in- 

 ternal iliac veins. Thence it 

 runs forward beneath the 

 vertebral column slightly to 

 one side of and close to the 

 aorta up to the liver, in the 

 dorsal surface of which it 

 becomes embedded. It enters 

 the thorax through an aper- 

 ture in the central tendon of 

 the diaphragm, and runs forward slightly to the right of the middle 



FIG. 105. Diagram of the venous 

 system of Lepus. 



A., azygos ; A.F., anterior facial ; E.I., external 

 iliac ; F., femoral ; G., genital ; H., hepatic ; I., in- 

 tercostals ; 1. 1., internal iliac ; I.L., ilio-lumbar ; 

 L.E., left anterior epigastric ; L.Ex., left external 

 jugular ; L.I., left internal jugular ; L.P., left 

 pre-caval; L.S., left sub-clavian; P., phrenics ; 

 P.C., ppst-caval ; P.P., posterior facial; R., renal; 

 R.A., right anterior intercostal ; R.E., right anterior 

 epigastric ; R.Ex., right external jugular ; R.I., 

 right internal jugular ; R.P. , right pre-caval ; R.S., 

 right sub-clavian ; V., vesicular. 



