4 DEFINITIONS. SECT. II. i. 6. 



their correfpondent veins. The pulmonary artery receives the 

 blood from the right chamber of the heart, and carries it to the 

 minuce extenfive ramifications of the lungs, where it is expoied 

 to the a&ion of the air on a furface equal to that of the whole 

 external fkin, through the thin moift coats of thofe veiTels, which 

 are fpread on the air-cells, which conftitute the minute terminal 

 ramifications of the wind-pipe. Here the blood changes its 

 colour from a dark red to a bright fcarlet. It is then collected 

 by the branches of the pulmonary vein, and conveyed to the 

 left chamber of the heart. 



6. The aorta is another large artery, which receives the blood 

 from the left chamber of the heart, after it has been thus aera- 

 ted in the iungs, and conveys it by afcending and defcending 

 branches to every part of the fyftem ; the extremities of this ar- 

 tery terminate either in glands, as the falivary glands, lachrymal 

 glands, &c. or in capillary veflels, which are probably lefs invo- 

 luted glands ; in thefe fome fluid, as falva, tears, perfpiration, is 

 fe^arateu from the blood j and the remainder of the blood is 

 abiorbed or drank up by branches of veins correfpondent to the 

 branches of the artery ; which are furnifhed with valves to prevent 

 its return ; and is thus carried back, after having again changed 

 its colour to a dark red, to the right chamber of the heart. The 

 circulation of the blood in the liver differs from this general fyf- 

 tem ; for the veins which drink up the refluent blood from thofc 

 arteries, which fpread on the bowels and mefentery, unite into 

 a trunk in the liver, and form a kind of artery which is branch- 

 ed into the whole fubftance of the liver, and is called the vena 

 portarum 5 and from which the bile is feparated by the numer- 

 ous hepatic glands, which conftitute that vifcus. 



7. The glands may be divided into three fyftems, the convo- 

 luted glands, fuch as thofe above defcribed, which feparate bile, 

 tears, faliva, c. Secondly, the glands without convolution, as 

 the capillary veflels, which unite the terminations of the arteries 

 and veins and feparate both the mucus, which lubricates the cel- 

 lular membrane, and the perfpirable matter, which preferves the 

 fkin moift and flexible. And thirdly, the whole abforbent fyftem, 

 confiding of the ladeals, which open their mouths into the ftom- 

 ach arid inteftines,andof the lymphatics, whichopen their mouths 

 on the external furface of the body, and on the internal linings of all 

 the cells of the cellular membrane, and other cavities of the body. 

 Thefe lacteal and lymphatic veflels are furnifhed with nu- 

 merous valves to prevent the return of the fluids, which they 

 abforb, and terminate in glands called lymphatic glands, and 

 may hence be confidered as long necks or mouths belonging to, 

 thefe glands. To thefe they convey the chyle and mucus, with 



