196 ANATOMY AND PHYSIOLOGY 



Collateral Circulation. An important descending branch of the occipital 

 artery runs down under the deep muscles of the neck to unite with one de- 

 rived from a branch of the subclavian, thus making a short route between the 

 subclavian and the external carotid; the blood can flow in this indirect way 

 to the head if the external carotid be ligated. 



PRINCIPAL ARTERIES OF THE TRUNK 



The thoracic aorta extends from the fourth dorsal vertebra 

 to the diaphragm (Fig. 135). 



Branches. Intercostal, n pairs, to the intercostal spaces; 

 bronchial to lung tissues; 1 pericardial to pericardium; esophageal 

 to esophagus, and mediastinal to glands and tissues between the 

 lungs (in the mediastinum, p. 365). 



Note.- These aortic intercostal arteries run rather more than half way to 

 the front, in grooves under the borders of the ribs, accompanied by inter- 

 costal nerves and veins to meet intercostal branches of the internal mammary 



The abdominal aorta extends from the opening in the dia- 

 phragm to the body (lower border) of the fourth lumbar vertebra 

 a little above the level of the umbilicus (Fig. 134). 



Branches. Phrenic to the diaphragm and lumbar (4 pairs) to 

 the abdominal wall, sacral to sacrum and rectum. 



Branches to viscera: The celiac artery, dividing into gastric, for 

 the stomach; hepatic, for the liver; 2 splenic (or lienaT), for the 

 spleen. 



Superior mesenteric, to the small intestine and these parts of 

 the large intestine, namely cecum, ascending colon, transverse 

 colon. 



Inferior mesenteric, to the remainder of the large intestine, 

 namely descending colon, sigmoid colon, rectum. 



Two renal arteries, to the kidneys. 



Adrenal arteries, to the adrenal bodies. 



The ovarian arteries, to the ovaries, or the spermatic arteries to 

 the testes. 



1 Bronchial arteries have very little to do with respiration; they are the nutrient 

 arteries of the lungs. 



* The hepatic circulation is a double one: Both venous and arterial blood enter 

 the liver. The portal vein (with products of digestion for the liver to work over) and 

 the hepatic artery (with the oxygen with which this work is to be done) enter together 

 through the portal fissure. (The venous blood of both leaves the liver by hepatic 

 veins, page 209.) 



