722 THE POPULAR SCIENCE MONTHLY, 



of the third eyelid, the rudimentary tail-bones, and many others, is 

 not satisfactorily accounted for on the theory of the plan of general 

 unity ; but if we look upon them as parts which have become func- 

 tionless and atrophied from want of use, and by heredity have been 

 transmitted from generation to generation, a bright light is thrown on 

 the reason of their existence. In the present paper I do not intend 

 to dwell on the significance of rudimentary organs which exist normal- 

 ly in man, but shall confine myself to those structures which occur as 

 variations. 



I might here mention that some parts, as for instance certain mus- 

 cles of the thumb, occur in man, but not in the lower animals ; these 

 we may take as indications of the advance of man to a still higher 

 development. 



To the study of embryology we owe much in elucidating many 

 morphological problems, and removing others from the domain of 

 theory. By our knowledge of this most intricate subject the signifi- 

 cance of many variations and rudimentary organs is made plain. 



It has been well said that " the development of the individual is 

 the compressed development of the race in the process of compression ; 

 some features are suppressed or modified, and others are thrown into 

 relief." In the development of the embryo we see the history of the 

 race, but the higher the form the more quickly does the embryo pass 

 through those stages and transformations which are the equivalent 

 of what is persistent in types below. In lower forms these stages are 

 much less rapid, and in fact are true metamorphoses. The changes 

 occurring in the development of the common frog will furnish a fa- 

 miliar example of this latter statement. The more we know of em- 

 bryology, the more the truth of the saying that " development means 

 descent " is apparent. 



It may not be generally known that no two individuals have ex- 

 actly the same anatomical structure, and that nearly every one has 

 in him some bony prominence, supernumerary muscle, or abnormal 

 blood-vessel, which tells the tale of his descent. During the past nine 

 years I have been teaching anatomy, and nearly three hundred sub- 

 jects have been dissected under my immediate supervision ; in these 

 I have carefully noted the variations occurring, with the result of find- 

 ing that scarcely one body is perfectly normal in every part — nay, 

 many are very abnormal, having as many as thirty to forty variations 

 in their bones, muscles, or arteries. I have found variations to occur 

 more frequently in negro and Indian subjects than in those of Euro- 

 pean descent. When a variation in a bone, muscle, or blood-vessel is 

 found, the first question asked is. What is its morphology ? and it is 

 the exception not to be able to make it out ; if one fails, it is concluded 

 that our knowledge is deficient, and that the variation has a history, 

 if we could only discover it. 



Many variations are explained when an appeal is made to compara- 



