AND THEIR FUNCTIONS. 151 



tained air rather than blood. It was against this belief 

 that Galen directed his attacks, when he contended that the 

 arteries were filled with blood, However, according to Sir 

 M. Foster, the Galenic philosophy set forth that, when the 

 heart expands, it draws air from the lungs, through what 

 are now known as the pulmonary veins, into the left ventricle, 

 and this air mixes there with blood which has passed 

 through invisible pores in the septum between the ventricles.* 

 This shows how lasting was Empedocles' conception of the 

 minute passages. 



Aristotle says that, in oviparous animals, such as birds, 

 and oviparous quadrupeds, the parts of the lungs are separ- 

 ated so much from each other that there appear to be two 

 distinct lungs,! and that, in snakes, there is a single lung 

 divided by a long " fibrous " tube.t 



Except that the trachea is only partly fibrous, this is 

 true of the lungs of the viper and grass-snake, which were 

 those best known to Aristotle. Some snakes, like the boa 

 and python, have two functional lungs, unequally developed. 



He says that the lungs of oviparous animals, e.g., lizards, 

 tortoises, and birds, are small and dry but capable of great 

 expansion, when inflated. § This assertion is qualified by a 

 passage in P. A. iii. c. 8, 671a, where he says that the 

 marine tortoises have flesh-like lungs containing blood, like 

 the lungs of oxen, and that the lungs of land tortoises are 

 larger proportionally than those of other oviparous quad- 

 rupeds. Compared with those of many oviparous animals, 

 the lungs of marine and also land tortoises are large and 

 fleshy, but they are not nearly as fleshy as those of an ox. 

 Aristotle's statement about the lungs of birds is inaccurate, 

 for the lungs of birds are rather large and contain much blood. 

 They are hidden to a large extent in recesses on each side of 

 the backbone, and it is probable that he never removed them 

 in order to examine them. 



By means of the currents of water bathing the gills, 

 Aristotle believed that fishes were cooled, but this was not 

 the only function of the gills, for he says that they serve 

 also as organs of smell. |i 



His descriptions of the gills of fishes are often difficult 

 to understand. He says correctly that the gills are either 

 single or double, and that the numbers of gills are equal on 



'- Led. on the Hist, of Physiology, 1901, pp. 12 and 13. 

 // \ H. A. i. c. is; s. 7. I Ibid. n. c. 12, s. 12. 



^ P. A. iii. c. 6, 669a. || Ibid. ii. c. 16, 659&. 



