148 DARWINISM STATED BY DARWIN HIMSELF. 



ably in length within the same genus : thus in some spe- 

 cies of Macacus it is longer than the whole body, and is 

 formed of twenty-four vertebrae ; in others it consists of 

 a scarcely visible stump, containing only three or four 

 vertebras. In some kinds of baboons there are twenty-five, 

 while in the mandrill there are ten very small stunted cau- 

 dal vertebrae, or, according to Cuvier, sometimes only five. 

 The tail, whether it be long or short, almost always tapers 

 toward the end ; and this, I presume, results from the 

 atrophy of the terminal muscles, together with their ar- 

 teries and nerves, through disuse, leading to the atrophy 

 of the terminal bones. But no explanation can at present 

 be given of the great diversity which often occurs in its 

 length. Here, however, we are more specially concerned 

 with the complete external disappearance of the tail. 

 Professor Broca has recently shown that the tail in all 

 quadrupeds consists of two portions, generally separated 

 abruptly from each other ; the basal portion consists of 

 vertebrae, more or less perfectly channeled and furnished 

 with apophyses like ordinary vertebrae ; whereas those 

 of the terminal portion are not channeled, are almost 

 smooth, and scarcely resemble true vertebrae. A tail, 

 though not externally visible, is really present in man 

 and the anthropomorphous apes, and is constructed on 

 exactly the same pattern in both. In the terminal por- 

 tion the vertebrae, constituting the os coccyx, are quite 

 rudimentary, being much reduced in size and number. 

 In the basal portion, the vertebrae are likewise few, are 

 united firmly together, and are arrested in development ; 

 but they have been rendered much broader and flatter 

 than the corresponding vertebrae in the tails of other ani- 

 mals ; they constitute what Broca calls the accessory 

 sacral vertebrae. These are of functional importance by 

 supporting certain internal parts and in other ways ; and 



