CH. XVIII.] 



COURSE OF THE CIRCULATION 



of fibrous tissue, is a small fibrous nodule, the corpus Arantii, and 

 from this and from the attached border fine fibres extend into every 

 part of the mid substance of the valve, except a small lunated space 

 just within the free edge, on each side of the corpus Arantii. Here 

 the valve is thinnest, and composed of little more than the endo- 

 cardium. Thus constructed and attached, the three semilunar 

 pouches are placed side by side around the arterial orifice of each 

 ventricle; they are separated by the blood passing out of the 

 ventricle, but immediately afterwards are pressed together so as to 



Pulmonary artery. 



Superior cava or vein 

 from head and neck. 



Right auricle. 

 Inferior vena cava- 



Right ventricle. 



Portal circulation. 



Second renal circu- 

 lation. 



Pulmonary capillaries. 



Pulmonary veins. 

 Aorta. 



Arteries to head and 

 neck. 



Left auricle. 



Left ventricle. 



Gastric and intestinal 

 vessels. 



...First renal circulation. 



_.Hystemic capillaries. 



FIG. 222. Diagram of the circulation. 



prevent any return (6, fig. 217, and 7, fig. 218). Opposite each of 

 the semilunar cusps, both in the aorta and pulmonary artery, there 

 is a bulging outwards of the wall of the vessel : these bulgings are 

 called the sinuses of Valsalva. The valves of the heart are formed 

 of a layer of closely woven connective and elastic tissue, over which, 

 on every part, the endocardium is reflected. 



Course of the Circulation. 



The blood is conveyed away from the left ventricle (as in the 

 diagram, fig. 222) by the aorta to the arteries, and returned to the 



