APPENDIX 



is shortened and the vertebrae have become thin and closely 

 packed together to support the large head, and how the 

 breast-bone is reduced and the ribs so loosely articulated to 

 the vertebral column that the huge lungs have full power 

 of expansion. All these are necessary modifications of the 

 mammalian skeleton which have been caused by the change 

 from a terrestrial to an aquatic existence. 



The lungs of the Cetacea are unlobulated and of extraor- 

 dinary size; the diaphragm, the muscular partition which 

 separates the thoracic from the abdominal cavity, is oblique, 

 and the brain greatly convoluted and of a high type; the 

 brain is especially notable for the loss of the olfactory, or 

 smelling portions, which are of no use to an aquatic mammal. 



Thus it is apparent in a review of only the most obvious 

 changes what a wonderful example of adaptation to environ- 

 ment is furnished by the Cetacea. 



