THE SCAFFOLDING LEFT IN THE BODY 117 



flies from the skin, or for erecting the hair of the 

 scalp, are common among quadrupeds, and these 

 are represented in the human subject by the still 

 functioning muscles of the forehead, and occasion- 

 ally of the head itself. Everyone has met persons 

 who possess the power of moving the whole scalp 

 to and fro, and the muscular apparatus for effect- 

 ing it is identical with what is normally found in 

 some of the Quadrumana. 



Another typical vestigial structure is the plica 

 semi-lunariSy the remnant of the nictitating mem- 

 brane characteristic of nearly the whole vertebrate 

 sub-kingdom. This membrane is a semi-transparent 

 curtain which can be drawn rapidly across the ex- 

 ternal surface of the eye for the purpose of sweeping 

 it clean. In birds it is extremely common, but it 

 also exists in fish, mammals, and all the other 

 vertebrates. Where it is not found of any functional 

 value it is almost always represented by vestiges of 

 some kind. In Man all that is left of it is a little 

 piece of the curtain draped at the side of the eye. 



Passing from the head to the other extremity of 

 the body one comes upon a somewhat unexpected 

 but very pronounced characteristic — the relic of 

 the tail, and not only of the tail, but of muscles 

 for wagging it. Everyone who first sees a human 

 skeleton is amazed at this discovery. At the end 



