48 THE DESCENT OF MAN. 



variations, makes the following pregnant remark: "Notable 

 departures from the ordinary type of the muscular struct- 

 ures run in grooves or directions, which must be taken to 

 indicate some unknown factor, of much importance to a 

 comprehensive knowledge of general and scientific an- 

 atomy."* 



That this unknown factor is reversion to a former state 

 of existence may be admitted as in the highest degree 

 probable, f It is quite incredible that a man should through 

 mere accident abnormally resemble certain apes in no less 

 than seven of his muscles, if there had been no genetic con- 

 nection between them. On the other hand, if man is de- 

 scended from some ape-like creature, no valid reason can 

 be assigned why certain muscles should not suddenly reap- 

 pear after an interval of many thousand generations, in the 

 same manner as with horses, asses, and mules, dark col- 

 ored stripes suddenly reappear on the legs, and shoulders, 

 after an interval of hundreds, or more probably of thous- 

 ands of generations. 



These various cases of reversion are so closely related to 

 those of rudimentary organs given in the first chapter, that 

 many of them might have been indifferently introduced either 

 there or here. Thus a human uterus furnished with cornua 



*The Rev. Dr. Haughton, after giving (" Proc. R. Irish. Academy," 

 June 27, 1864, p. 715) a remarkable case of variation in the human 

 flexor pollicis longus, adds : ' ' This remarkable example shows that 

 man may sometimes possess the arrangement of tendons of thumb 

 and fingers characteristic of the macaque ; but whether such a case 

 should be regarded as a macaque passing upward into a man, or a 

 man passing downward into a macaque, or as a congenital freak of 

 nature, I cannot undertake to say." It is satisfactory to hear so 

 capable an anatomist, and so embittered an opponent of evolutionism, 

 admitting even the possibility of either of his first propositions. 

 Prof. Macalister has also described (" Proc. R. Irish Acad.," vol. x, 

 1864, p. 138) variations in the flexor pollicis longus, remarkable from 

 their relations to the same muscle in the Quadrumana. 



f Since the first edition of this book appeared, Mr. Wood has pub- 

 lished another memoir in the "Phil. Transactions," 1870, p. 83, on 

 the varieties of the muscles of the human neck, shoulder, and chest. 

 He here shows how extremely variable these muscles are, and how 

 often and how closely the variations resemble the normal muscles of 

 the lower animals. He sums up by remarking: " It will be enough 

 for my purpose if I have succeeded in showing the more important 

 forms which, when occurring as varieties in the human subject, tend 

 to exhibit in a sufficiently marked manner what may be considered as 

 proofs and examples of the Darwinian principle of reversion, or law 

 of inheritance, in this department of anatomical science." 



