The Ascent of Man 157 



anatomists have made out a list of over a hundred of these ves- 

 tigial structures, and though this number is perhaps too high, 

 there is no doubt that the list is long. In the inner upper corner 

 of the eye there is a minute tag but larger in some races than in 

 others which is the last dwindling relic of the third eyelid, used 

 in cleaning the front of the eye, which most mammals possess in 

 a large and well-developed form. It can be easily seen, for in- 

 stance, in ox and rabbit. In man and in monkeys it has become 

 a useless vestige, and the dwindling must be associated with the 

 fact that the upper eyelid is much more mobile in man and mon- 

 keys than in the other mammals. The vestigial third eyelid in 

 man is enough of itself to prove his relationship with the mam- 

 mals, but it is only one example out of many. Some of these are 

 discussed in the article dealing with the human body, but we may 

 mention the vestigial muscles going to the ear-trumpet, man's 

 dwindling counterpart of the skin-twitching muscle which we 

 see a horse use when he jerks a fly off his flanks, and the short tail 

 which in the seven-weeks-old human embryo is actually longer 

 than the leg. Without committing ourselves to a belief in the 

 entire uselessness of the vermiform appendix, which grows out 

 as a blind alley at the junction of the small intestine with the 

 large, we are safe in saying that it is a dwindling structure the 

 remains of a blind gut which must have been capacious and useful 

 in ancestral forms. In some mammals, like the rabbit, the blind 

 gut is the bulkiest structure in the body, and bears the vermiform 

 appendix at its far end. In man the appendix alone is left, and 

 it tells its tale. It is interesting to notice that it is usually longer 

 in the orang than in man, and that it is very variable, as dwindling 

 structures tend to be. One of the unpleasant expressions of this 

 variability is the liability to go wrong: hence appendicitis. Now 

 these vestigial structures are, as Darwin said, like the unsounded, 

 i.e. functionless, letters in words, such as the o in "leopard," 

 the b in "doubt," the g in "reign." They are of no use, but they 

 tell us something of the history of the words. So do man's ves- 



