66 THE DESCENT OF MAN. 



constituting the os coccyx, are quite rudimentary, being 

 much reduced in size and number. In the basal portion, 

 the vertebras are likewise few, are united firmly together, 

 and are arrested in development ; but they have been ren- 

 dered much broader and natter than the corresponding 

 vertebrae in the tails of other animals ; they constitute 

 what Broca calls the accessory sacral vertebrae. These are 

 of functional importance by supporting certain internal 

 parts and in other ways ; and their modification is directly 

 connected with the erect or semi-erect attitude of man and 

 the anthropomorphous apes. This conclusion is the more 

 trustworthy, as Broca formerly held a different view, which 

 he has now abandoned. The modification, therefore, of 

 the basal caudal vertebrae in man and the higher apes. may 

 have been affected, directly or indirectly, through natural 

 selection. 



But what are we to say about the rudimentary and 

 variable vertebrae of the terminal portion of the tail, form- 

 ing the os coccyx 9 A notion which has often been, and will 

 no doubt again be, ridiculed, namely, that friction has had 

 something to do with the disappearance of the external 

 portion of the tail, is not so ridiculous as it at first appears. 

 Dr. Anderson* states that the extremely short tail of Maca- 

 cus brunneus is formed of eleven vertebrae, including the 

 imbedded basal ones. The extremity is tendinous and 

 contains no vertebrae; this is succeeded by five rudimentary 

 ones, so minute that together they are only one line and a 

 half in length, and these are permanently bent to one side 

 in the shape of a "hook. The free part of the tail, only a 

 little above an inch in length, includes only four more 

 small vertebrae. This short tail is carried erect; but about 

 a quarter of its total length is doubled on to itself to the 

 left; and this terminal part, which includes the hook-like 

 portion, serves " to fill up the interspace between the upper 

 divergent portion of the calosities;" so that the animal sits 

 on it and thus renders it rough and callous. Dr. Anderson 

 thus sums up his observations : " These facts seem to me 

 to have only one explanation; this tail, from its short size, 

 is in the monkey's way when it sits down, and frequently 

 becomes placed under the animal while it is in this atti- 

 tude; and from the circumstance that it does not extend 



*"Proc. Zoolog.^Soc." 1872, p. 210. 



