Page:Popular Science Monthly Volume 25.djvu/740

722 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 functionless 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 normally in man, but shall confine myself to those structures which occur as variations.

I might here mention that some parts, as for instance certain muscles 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 significance 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 familiar example of this latter statement. The more we know of embryology, the more the truth of the saying that "development means descent" is apparent.

It may not be generally known that no two individuals have exactly 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 subjects have been dissected under my immediate supervision; in these I have carefully noted the variations occurring, with the result of finding 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 European 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