136 AEISTOTLE S ANHOMCEOMBEIA 



newt, have no scutes, and the chamseleon, which Aristotle 

 knew so well, is covered by granules which can be very 

 easily scraped off by means of a knife. 



For some time past attempts have been made to ascer 

 tain the ages of fishes by an examination of their scales. 

 Aristotle also refers to changes in the nature of the scales of 

 fishes with advancing age, saying that they become harder 

 and thicker, and much harder in fishes which are old and 

 wasted.* 



B. THE HEART AND BLOOD-VESSELS. 



Aristotle s description of the heart and the arrangement 

 of the blood-vessels constitutes his most valuable contri 

 bution to anatomical knowledge. Before his time it was 

 generally believed that the origins of the blood-vessels were 

 in the head, and in his H. A. iii. c. 2, he gives the arrange 

 ments of the blood-vessels according to Syennesis of Cyprus, 

 Diogenes of Apollonia, and Polybus, w r ho scarcely mention 

 the heart. He was the first to explain, in clear language, 

 that the blood-vessels arise from the heart, but he cannot 

 be regarded with certainty as the originator of this dis 

 covery, for Plato says that the heart is the bond of union of 

 the blood-vessels, and the fountain of the blood coursing 

 through the limbs, t 



Aristotle s reasons for believing that the heart is the 

 origin of the blood-vessels are given in P. A. iii. c. 4, where 

 he says that the blood-vessels necessarily have one origin, 

 for, where it is possible, it is better that there should be one 

 and not many. This origin, he says, is in the heart, for the 

 blood-vessels extend from it and not through it, and it 

 occupies a very important or controlling position in the 

 body. Then, after asserting that those are mistaken who 

 believe that the blood-vessels have their origins in the head, 

 he shows that the heart should be in a hot part of the body, 

 and that it is so situated and is well adapted to be the origin 

 and to form part of the arrangement of blood-vessels, for it 

 has thick walls to prevent loss of heat, and is of the nature 

 of a reservoir, the blood passing from it to the vessels, but 

 not returning. All this, he says, is clearly proved by means 

 of dissections and the phenomena of development, for the 

 heart is the first part to be formed and contains blood as 

 soon as it is formed. 



* H. A. iii. c. 10, s. 10. f Timasus, 70. 



