I 



62 



AORTAL ARTERIES 



Sect. V. 2. 



the lungs of air-breathing animals ; but the pulmonary vein, taking 

 the ftrudure of an artery, after having received the blood from the 

 gills, which there gains a more florid colour, diftributes it to the other 

 parts of their bodies. A fimilar ftrufture obtains in the livers of fifli, 

 as well as in thofe of air-breathing animals ; the blood is colleded 



proper 



\ 



from the mefentery and inteftines by the branches of their 

 veins, which unite on their entrance into the liver, branch out 

 again, and aflume the office of an artery, under the name of vena 

 portarum, diftributing the blood through that large vifcus for the 

 purpofe of the fecretion of bile; whence we fee in thefe animals 

 two circulations independent of the power of the heart. Firft, that 

 which begins in the mefentery and inteftines, and pafles through the 

 liver ; and fecondly, that beginning at the termination of the veins 

 of the gills, and paffing through the other parts of the body; both 

 which circulations are carried on by the adion of thofe refpedive ar- 



> 



teries and veins. Monro's Phyfiology of Fifh, p. 19, 



The courfe of the fluids in the leaves, and in the trunks and roots 

 of vegetables, is performed in a fimilar manner. Firft,,the abforbent 

 vefl!els of the roots, of the internal cells, and of the external bark, with 



the 



blood returning from thofe parts 



the foot-ftalk 



of the Jeaf; and then, like the vena portarum, an artery commence 

 without the intervention of a heart, and receiving the fap and venoi 

 blood fpreads it in numerous ramifications on the upper furface of th 

 leaf; here it changes its colour, and becomes vegetable blood ; and i 



and 



\ 



the under fu 



again colle6:ed by a pulmonary vein, 

 face of the leaf. This vein, like that which receives the blood from 

 the gills of fifli, affumes the oflBce of an artery, which correfponds 

 with the aorta of animals, and branching again difperfes the blood 

 ■upward to the plumula or fummit of th^ bud, from its caudex at the 

 fcot-ftalk of the leaf, and downward along the bark of the trunk to 

 the roots; where it is received by a vein correfponding to th 



©f animals, after having expended what 



quired for th 



fccre 



tions 



f 



