EUDIMENTARY ORGANS OF ANIMALS 143 



There are thirteen dorsal vertebrae. With the 

 exception of that which has just been described, 

 they consist of : a centrum, neurapophyses, and a 

 pair of fully developed ribs ; the intercentra has 

 completely disappeared, and the hsemapophyses, 

 which form the head and neck of the rib, are in a 

 reduced condition. In the five lumbar vertebrae 

 which follow, the rib disappears, or to speak more 

 accurately, the transverse processes are all that 

 remain of what were the ribs, and have ossified 

 with the vertebra. 



The sacrum is a region profoundly modified to 

 support the pelvic basin. It is formed by the 

 fusion of five vertebrae, each consisting of a 

 centrum, neurapophyses, and short bicipital ribs. 

 The first three vertebrae are the true sacrals, as 

 these alone support the basin ; the two following are 

 really caudal vertebrae in process of fusion with the 

 sacrum. In monkeys other than anthropoids there 

 are really only three sacral vertebrae and these are 

 at once succeeded by the tail. In man, the tail 1 

 consists of six vertebrae of which the two first 

 which consist of a centrum and neurapophyses and 

 of bicipital ribs have fused with the sacrum, 

 while the four remaining lower vertebrae, which 

 consist of only the centra (the first still exhibits 

 rudimentary neurapophyses) have fused, and form 

 the coccyx. 



1 See Albrecht, La queue chez Vhomme (Bull. soc. Anthrop. 

 Brux., vol. iii., 1884-1885, 



