5 8 The Descent of Man. Taut I. 



became divested of hair for ornamental purposes, as we shall see 

 under Sexual Selection ; an J, according to this belief, it is not 

 surprising that man should differ so greatly in hairiness from all 

 other Primates, for characters, gained through sexual selection, 

 often differ to an extraordinary degive in closely-related foims. 



According to a popular impression, the absence of a tail is 

 eminently distinctive of man ; but as those apes which come 

 nearest to him are destitute of this organ, its disappearance does 

 aot relate exclusively to man. The tail often differs remarkably 

 in length within the same genus : thus in some species 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, whilst in the mandrill there are 

 ten very small stunted caudal vertebrae, or, according to Cuvier, 90 

 sometimes only five. The tail, whether it be long or short, almost 

 always tapers towards the end ; and this, I presume, results from 

 the atrophy of the terminal muscles, together with their arteries 

 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 dis- 

 appearance of the tail. Professor Broca has recently shewn 91 

 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 channelled and furnished with 

 apophyses like ordinary vertebrae ; whereas those of the terminal 

 portion are not channelled, 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 

 portion 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 animals : they constitute what 

 Broca calls the accessory sacral vertebras. These are of functional 

 importance by supporting certain internal parts and in other 

 ways; and tleir modification is directly connected with the erect 



90 Mi St. George Mivart, • Proc. Geoffrey, ' Hist. Nat. Gen.' torn. ii. 



Zoolog. Soc' 1865. yp. 56:J, 583. p. 244. 



Dr. J. E. Gray, 'Cat. Brit. Mus.J 91 'Revue d' Anthropologic,' 1872 ; 



Skeletons.' Owen, 'Anatomy of ' La Const, tv.t'on des Vertebras cau 



Vertebrates,' vol. ii. p, 517. Isidore d^lea.' 



