254 THE VITAL FUNCTIONS. 



with quadrupeds ; for in the latter the heart is 

 placed directly in the middle of the chest, with the 

 point towards the abdomen, and not occupying any 

 portion of the diaphragm ; but in man, the heart 

 lies obliquely on the diaphragm, with the apex 

 turned towards the left side. 



The communications of the capillary arteries with 

 the veins are beautifully seen, under the micro- 

 scope, in the transparent membranes of frogs or 

 fishes. The splendid spectacle, thus brought within 

 the cognizance of our senses, of unceasing activity 

 in the minutest filaments of the animal frame, and 

 of the rapid transit of streams of fluid, bearing 

 along with them minute particles, which appear to 

 be pressing forwards, like the passengers in the 

 streets of a crowded city, through multitudes of 

 narrow and winding passages, can never fail, when 

 first beheld, to fill the mind with astonishment ;* 

 a feeling, which must be exalted to the highest ad- 

 miration on reflecting that what we there behold is 

 at all times going on within ais, during the whole 

 period of our lives, in every, even the minutest por- 

 tion of our frame. How inadequate, then, must be 

 any ideas we are capable of forming of the incal- 

 culable number of movements and of actions, w hich 

 are conducted in the living system ; and how infi- 

 nite must be the prescience and the wisdom, by 



* Leuwenhoeck, speaking of the delight he experienced on viewing 

 the circulation of the blood in tadpoles, uses the following ex- 

 pressions. " This pleasure has oftentimes been so recreating to me, 

 that 1 do not believe that all the pleasure of fountains, or water- 

 works, either natural or made by art, could have pleased my sight 

 so well, as the view of these creatures has given me." — Phil. Trans, 

 xxii. 453. 



