108 THE VITAL FUNCTIONS. 



inner surface of the intestines, whence they 

 absorb, or drink up the chyle. They may be 

 compared to internal roots, which unite as they 

 ascend along the mesentery (m), or membrane 

 connecting the intestines with the back ; forming 

 larger and larger trunks, till they terminate in 

 an intermediate reservoir (u), which has been 

 named the Receptacle of the Chyle. From this 

 receptacle there proceeds a tube, which, from its 

 passing through the thorax, is called the Tho- 

 racic duct (t) : it ascends along the side of the 

 spine, which protects it from compression, and 

 opens, at v, into the large veins which are pour- 

 ing their contents into the auricle^ or first cavity 

 of the heart (u) ; whence it immediately passes 

 into the ventricle^ or second cavity of that 

 organ (h). Such, in the more perfect animals, 

 is the circuitous and guarded route, which every 

 particle of nourishment must take before it can 

 be added to the general mass of circulating 

 fluid. 



By its admixture with the blood already con- 

 tained in these vessels, and its purification by 

 the action of the air in the respiratory organs (b), 

 the chyle becomes assimilated, and is distri- 

 buted by the heart through appropriate chan- 

 nels of circulation called arteries (of which the 

 common trunk, or Aorta, is seen at a), to every 

 part of the system ; thence returning by the veins 

 (v, V, V,) to the heart. The various modes in 



