MANNER OF DEVELOPMENT. 65 



I know, acquired any specialized means of relief. The 

 view which seems to me the most probable is that man, or 

 rather primarily woman, became divested of hair for orna- 

 mental purposes, as we shall see under Sexual Selection; 

 and, 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 degree in closely related forms. 



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 disap- 

 pearance does not 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, while in the mandrill there are ten very small 

 stunted caudal vertebrae, or, according to Cuvier,* some- 

 times 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 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 disappearance of the 

 tail. Prof. Broca has recently shownf 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 anthro- 

 pomorphous apes, and is constructed on exactly the same 

 pattern in both. In the terminal portion of the vertebrae, 



*Mr. St. George Mivart, " Proc. Zoolog. Soc.," 1865, pp. 562, 583. 

 Dr. J. E. Gray, "Cat. Brit. Mus.: Skeletons." Owen, "Anatomy 

 of Vertebrates," vol. ii, p. 517. Isidore Geoffroy "Hist. Nat. Gen." 

 torn, ii, p. 244. 



f " Revue d'Anthropologie," 1872 ; " La Constitution des Vertebres 

 cau dales," 



