THE ABDOMINAL WALLS 



243 



into an upper and a lower group. The upper veins join the 

 internal mammary, intercostal, and lateral (long) thoracic veins, 

 and so return their blood to the heart via the vena cava superior. 

 The lower veins join the femoral, and consequently drain into 

 the vena cava inferior. These two groups communicate freely 

 with one another through the thoraco-epigastric vein, which 

 ascends from the groin to the region of the axilla. Owing to 

 their position these veins are capable of considerable increase 

 in size. In obstruction of the vena cava inferior this anastomosis 



Cerebral cortex in 

 connection with skin 



Cerebral cortex 

 in connection 

 with viscus 



Cells in anterior column of 

 spinal medulla 



FIG. 73. Diagram to illustrate the Viscero - Sensory and Viscero-Motor 

 Reflexes. The arrows indicate the passage of the afferent impulses from 

 the viscus to the cortex, and show how they may overflow so as to 

 stimulate the neighbouring cells in the spinal medulla. 



provides a new channel for the return of blood from the lower 

 limbs, and the thoraco-epigastric vein becomes specially enlarged. 

 Further, the para-umbilical vein (of Sappey) passes from the left 

 branch of the portal vein along the ligamentum teres to the 

 umbilicus, where it communicates with both groups. Varicosity 

 of the superficial abdominal veins may therefore occur in 

 portal obstruction, but in this case the blood -flow in the 

 distended veins is from the umbilicus both upwards and down- 

 wards, whereas in obstruction of the vena cava inferior the 

 blood-flow is in an upward direction only. 



The Lymph Vessels of the whole abdominal wall, below 

 the level of the umbilicus, join the superficial sub-inguinal lymph 



