80 ORGANIC EVOLUTION 



which unquestionably correspond to those employed 

 by the lower animals in moving the tail ; though 

 this power has lapsed in man even more completely 

 than the power of moving the external ear by the 

 degenerate muscles which are still attached to it, 

 even in adult man. But this is not all. In man 

 and other mammals — and indeed in other orders 

 of vertebrates as well — the supply of blood to the 

 posterior (in man the lower) portion of the body, is 

 conveyed by a large artery known as the aorta, 

 which runs backwards (in man downwards) akmg 

 the lower (in man, the front) aspect of the spinal 

 column. This great artery ultimately terminates 

 by a Y-shaped division into two large vessels, one 

 of which passes sidewards towards the left, and 

 the other towards the right lower limb. In the 

 obviously tailed animals there proceeds from the 

 point of division, or from just above it, a much 

 smaller artery which runs straight downwards along 

 the lower surface of the tail, thus continuing, alon^r 

 this terminal portion of the spinal column, the 

 course which the great aorta pursued along its first 

 portion. In the tailed animals this artery is known 

 as the caudal artery (Lat. cauda — the tail). Now 

 in the higher apes and in man, the " tail-less," there 

 is found, proceeding from the aorta in the same 

 manner, a minute artery which takes the same 

 course towards the coccyx, and which, in human 

 anatomy, is called the coccygeal artery. But every 

 comparative anatomist knows full well that this 

 so-called coccygeal artery is none other than the 

 caudal artery of the tiger or the ox or the mar- 

 mozet. Recalling the terms already defined, we 



