Rudiments. 47 



wanting in some individuals. Fig. 66 shows the most important of the 

 ear muscles. Occasionally we meet with a person who can work his 

 ears. I know one who can throw off his plug hat I suppose with the 

 attrahens alone; for it is said that while a few can use that muscle and 

 the retrahens, no one can use any of the rest. 



The lower apes as well as the other mammals generally, still use these 

 muscles. The anthropoid apes, however, do not as a rule. 



The anthropoid apes, as a rule, also share with man the round-edged 

 folded ear shell with its flap. Darwin has shown that the embryo of 

 some of the anthropoid apes has a long pointed ear, which is rounded 

 off afterwards. In many cases the faint hint of this point can still be 

 detected on the upper margin of the human ear. According to Darwin, 

 the drooping of dog's ears is due to the atrophy of the muscles through 

 disuse, since their domestication. 



The remains of a third eyelid is found in the inside corners of the 

 eyes of men and apes. It is simply in them a crescent-shaped fold of 

 membrane, covering a ve^ small part of the eye-ball. The fully de- 

 veloped membrane occurs in the primitive fishes, sharks, and some 

 other animals. In them it is used to cover and protect the eyeball. The 

 scrap of it left to man and ape is quite useless and immovable. 



The panniculus carnosus consists of a thin muscular sheet immedi- 

 ately under the skin, which the quadrupeds use for shaking the skin to 

 drive off flies. In man this muscle has largely disappeared, only three 

 pieces of it being left, viz. , the occipito frontalis, or muscle for moving 

 the skin of the forehead, the cremaster muscle, and the platysma my- 

 oides or skin muscle, situated on the sides of the neck. We have no 

 control, of this last muscle, the office of which would be, if we could use 

 it, to wrinkle the skin of the neck transversely. The risorius, however, 

 which helps us to laugh, is reckoned to be an active part of the other- 

 wise functionless platysma myoides. (See fig. 66 1, 3, 23, 24.) 



The thymus gland is a body which is formed near the base of the 

 heart. It is largely developed in the foetus, and it continues to grow 

 for two or three years after birth. After that time it remains without 

 change for a period of from 7 to 12 years. Fatty degeneration then be- 

 gins at the outer part of each lobule and proceeds inwards, and the or- 

 gan loses its activity. 



While the organ is functional it appears to be a lymph gland. In 

 reptiles and amphibians, which do not possess other lymph glands, this 

 seems to be sufficient in itself, and it remains active through their lives. 

 It forms colorless corpuscles identical with the colorless corpuscles 

 found in the blood. Useful in infancy, it is soon outgrown, and be- 

 comes a mere useless rudiment. It has become superseded by a more 

 complete apparatus, and is in process of total abolition. It is an inherit- 



