80 MOTION OF THE 



indeed, and that the blood may not regurgitate upon the pul- 

 monary veins, and thus the force of the ventricle in propelling 

 the blood through the system at large come to be neutralized, 

 it is that these mitral valves excel those of the right ventricle in 

 size and strength, and exactness of closing. Hence, too, it is 

 essential that there can be no heart without a ventricle, since 

 this must be the source and storehouse of the blood. The same 

 law does not hold good in reference to the brain. For almost 

 no genus of birds has a ventricle in the brain, as is obvious in 

 the goose and swan, the brains of \vhich nearly equal that of a 

 rabbit in size; now rabbits have ventricles in the brain, whilst the 

 goose has none. In like manner, wherever the heart has a single 

 ventricle, there is an auricle appended, flaccid, membranous, 

 hollow, filled with blood ; and where there are two ventricles, 

 there are likewise two auricles. On the other hand, however, 

 some animals have an auricle without any ventricle ; or at all 

 events they have a sac analogous to an auricle ; or the vein it- 

 self, dilated at a particular part, performs pulsations, as is seen 

 in hornets, bees, and other insects, which certain experiments 

 of my own enable me to demonstrate have not only a pulse, but 

 a respiration in that part which is called the tail, whence it is 

 that this part is elongated and contracted now more rarely, now 

 more frequently, as the creature appears to be blown and to 

 require a larger quantity of air. But of these things, more in 

 our Treatise on Respiration. 



It is in like manner evident that the auricles pulsate, con- 

 tract, as I have said before, and throw the blood into the ven- 

 tricles ; so that wherever there is a ventricle an auricle is ne- 

 cessary, not merely that it may serve, according to the general 

 belief, as a source and magazine for the blood : for what were 

 the use of its pulsations had it nothing to do save to contain ? 

 No ; the auricles are prime movers of the blood, especially the 

 right auricle, which is " the first to live, the last to die '" as 

 already said ; whence they are subservient to sending the blood 

 into the ventricle, which, contracting incontinently, more readily 

 and forcibly expels the blood already in motion; just as the 

 ball-player can strike the ball more forcibly and further if 

 he takes it on the rebound than if he simply threw it. 

 Moreover, and contrary to the general opinion, since neither 

 the heart nor anything else can dilate or distend itself so as to 



