CONSPECTUS OF ORGANS MENTIONED IN THE TEXT 205 



On glancing through this summary, it will be seen that the 

 arrangement of the subject matter is not altogether a natural 

 one; indeed, in introducing it, I have only sought to give a 

 classified survey of the contents of this book. 



Physiological considerations must determine the ultimate 

 method of grouping the facts, especially because, as was pointed 

 out in the introduction, the term vestigial is, as a rule, 

 only applied to such organs as have lost their original physio- 

 logical significance. Eetrogressive organs, on the contrary, are 

 such as may still remain functional, though, as a rule, only to 

 a limited extent. It has further been seen that both these 

 conditions in the process of degeneration may be, in different 

 individuals, realised in one and the same organ. The palmaris 

 longus and plantaris muscles furnish a case in point ; for while 

 these, and especially the former, are not infrequently so well 

 developed that there can be no doubt of their being functional, 

 cases occur in which one or the other of them has become quite 

 transformed into tendinous tissue and really vestigial. And in 

 yet other cases these muscles may altogether have disappeared. 

 On this subject Osborn makes the following appropriate remark : 

 " Both in the muscular and skeletal systems we find organs so 

 far on the down grade that they are mere pensioners of the body, 

 drawing pay (i.e. nutrition) for past honourable services without 

 performing any corresponding work the plantaris and palmaris 

 muscles for example." l 



Many similar examples might be given. Confining our 

 attention to muscles alone, it may suffice to recall the pyramidalis 

 and certain muscles of the head. 



1 Cf. this author's Cartwright Lectures, Lect. I. "The Contemporary Evolution 

 of Man," Medical Record, Feb. 20, 1892. 



