MAMMALIA 



313 



Fig. 255. Skull and spinal col- 

 umn and single vertebra of a com- 

 mon cotton-tail rabbit (Le'pus syl- 

 vat'icus) . (Cleaned and mounted by 

 students.) 



Fig. 256. Pelvic girdle of Jack-rab- 

 bit. (From dissection.) 



All mammals have ribs. They vary in number in different 

 groups, or, it may be, in different species. The greater number 



