PARTS OF ANIMALS, III. v.-vi. 



this is excessive ; and this excess may be due either 

 to the quantity of it or (since some substances are 

 less patient of concoction than others) to its quaUty. 

 (Haemorrhage occurs most where the passages are 

 widest, as from the nostrils, the gums and the 

 fundament, and occasionally from the mouth. At 

 these places it is not painful ; when, however, it 

 occurs from the windpipe, it is violent.) 



The Great Blood-vessel " and the Aorta, which in 

 the upper part are some distance from each other, 

 lower down change sides, and thus hold the body 

 compact. That is to say, when they reach the place 

 where the legs diverge, they divide into two, and 

 the Great Blood-vessel goes over to the back from 

 the front, and the Aorta to the front from the back ; 

 and thus they unite the body together, for this 

 changing over of the blood-vessels binds together 

 the front and the back of the body just as the cross- 

 ing of the strands in plaiting or twining makes the 

 material hold together more stoutly. A similar 

 thing occurs in the upper part of the body, where 

 the blood-vessels that lead from the heart are inter- 

 changed. For an exact description of the relative 

 disposition of the blood-vessels, the treatises on 

 Anatomy and the Researches upon Animals ^ should be 

 consulted. 



We have now finished our discussion of the heart 

 and the blood-vessels, and we must go on to consider 

 the remaining viscera on the same lines. 



VI. First the Lung. The reason why any group of Lung, 

 animals possesses a lung is because they are land- 

 creatures. It is necessary to have some means for 

 cooling the heat of the body ; and blooded animals 

 are so hot that this cooling must come from outside 



255 



