si FATHERS OF BIOLOGY. 



in blood in man than in any other animal ; and in men 

 than in women. This again explains why man alone 

 of animals stands erect. For the heat, overcoming any 

 opposite inclination, makes growth take its own line of 

 direction, which is from the centre of the body upwards. 

 . . . Man again has more sutures in his skull than any 

 other animal, and the male more than the female. The 

 explanation is to be found in the greater size of the 

 brain, which demands free ventilation proportionate to 

 its bulk. . . . There is no brain in the hinder part of 

 the head. . . . The brain in all animals that have one 

 is placed in the front part of the head . . . because the 

 heart, from which sensation proceeds, is in the front part 

 of the body," 



Although it would perhaps be difficult to find anywhere 

 as many errors in as few words, yet it should be observed 

 that Aristotle here shows himself to have been aware of 

 the existence of the membranes of the brain the pia 

 mater and the dura mater ; and elsewhere 1 he says more 

 explicitly, " Two membranes enclose the brain ; that 

 about the skull is the stronger; the inner membrane is 

 slighter than the outer one." And further, it should be 

 noted that he describes the latter membrane as a vascular 

 one. The fact of the brain substance being insensible to 

 mechanical irritation was known to Aristotle, and may 

 have been learnt from the practice of Hippocrates. 

 1 " History of Animals," i. 16. 



