282 THE EVOLUTION OF MAN. 



parent-form, from some Promammal whicli had seven neck- 

 vertebrte. If each animal species had been a distinct crea- 

 tion, it would have been far more to the purpose to have 

 furnished the long-necked Mammalia with a larger, and the 

 short-necked with a smaller number of neck-vertebrte. The 

 neck-vertebr£e are immediatelyfollowed by those of the breast 

 or thorax, which, in Man and most other Mammals, number 

 twelve or thirteen (usually twelve). Attached to the sides 

 of each breast- vertebra (Fig. 255) is a pair of ribs — long 

 curved processes of bone lying in and supporting the wall of 

 the thorax. The twelve pairs of ribs, with the connecting 

 intercostal muscles and the breast-bone (sternum) constitute 

 the breast -body (tJiorax, Fig. 252, p. 279). In this elastic 

 and yet firm thorax lie the double lung, and between the 

 two halves of this, the heart. The chest-vertebras are 

 followed by a short but massive section of the vertebral 

 column, formed by five large vertebrae. These are the 

 lumbar-vertebrae (Fig. 256), which bear no ribs and have 

 no perforations in their lateral processes. Next comes the 

 cross-bone (sacrum), which is inserted between the two 

 halves of the pelvic girdle. This cross-bone consists of five 

 fixed and amalgamated cross-vertebrte. Last comes a small 

 rudimentary tail- vertebral column, the rump-bone (coccyx). 

 This bone consists of a varying number (usually four, more 

 rarely three or five) of small aborted vertebrae ; it is a 

 useless rudimentary organ, retaining no physiological sig- 

 nificance either in Man or in the Tail-less Apes or Anthro- 

 poids. (C£ Figs. 204-208.) Morphologically it is, however, 

 very interesting, as affording incontrovertible evidence of 

 the descent of Man and of Anthropoids from Long- tailed 

 Apes. For this assumption affords the only possible 



