414 



THE MECHANICAL FUNCTIONS. 



tant viscera are placed forwards, and crowded 

 towards the head. No room is allowed for a 

 neck ; and the abdomen may be almost regarded 

 as continuous with the head, there being properly 

 no intervening thorax ; for the respiratory organs 

 are situated rather beneath than behind the 

 head. All this has been done with a view to 

 leave ample scope for the prolonged expansion 

 of the coccygeal vertebrae, and of their muscles, 

 which compose more than half the bulk of the 

 animal. 



Having seen how all impediments to the free 

 motion of the tail have been carefully removed, 

 let us next inquire into the mechanism by which 

 mobility has been given to that organ. The first 

 peculiarity we meet with in the structure of 

 the spine of fishes is the mode in which the 

 vertebrae are connected together. The bodies of 



189 



each vertebra, as may be seen in Figures 186 

 and 187, are hollowed out, both before and 



