378 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



side and the venous trunks on the other. This is merely 

 for convenience of diagrammatic representation. Real- 

 ly they lie close together 

 along the backbone, as if 

 the diagram were folded 

 along the middle backward. 

 Again, of course, the aorta 

 in its lower part divides 

 into two branches to sup- 

 ply the legs, and similarly 

 the great branches going 

 upward divide to supply the 

 arms and head. These are 

 not represented. 



For pure purposes of 

 physiology the formula ex- 

 pressed in these diagrams 

 is sufficient. But there is 

 so peculiar a significance in 

 relation to evolution in the 

 great outgoing (not incom- 

 ing) vessels of the heart 

 that a more particular ac- 

 count of these is necessary. 

 The aorta coming out of 

 the left ventricle (Fig. 260), 

 as already seen, makes an 

 arch to the left and goes 

 down to form the abdomi- 

 nal aorta. From the top 

 of the arch it sends off up- 

 ward three branches. The 



pv- 



Fig. 259. — Diagram showing course 

 of circulation, more in detail : T 

 and T\ tissues ; h, hepatic artery ; 



sfi, splenic artery ; m. mesenteric £;-,,*. :„ 4.1 ■ i_.. • 1 r 



1; r, renal " rSt 1S 0n tne n g nt Side of 



artery ; pv, portal vein 

 artery ; I/, heart ; L, lu: 

 arrows show the cour 

 circulation. (After Dalton.) 



artery ; H, heart ; L, lungs. The the arch (left in the dia- 

 arrows show the course of the . v 



gram). This again divides 



