20 



^re called the spine), not solidly but by the inter- 

 vention of muscles; so that, although the arms 

 must, in all completed motions, finally conform to 

 the movements of the back-bone, they have yet a 

 certain liberty of action, superior to that of the legs, 

 and which is determined rather by their connec- 

 tions with the head and neck, than by their union 

 with other parts. The arms are therefore more 

 particularly Jiead-limbs,^ while the legs may be 

 called body limbs. 



§ 9. We, therefore, assume that, so far as the 

 skeleton is concerned, motion originates in the spine, 

 is directed by the head, and is only followed up by the 

 limbs. 



§ 10. The researches of comparative anatomists 

 have demonstrated, that the closest analogy exists 

 between relative parts of all the animals classed 

 as vertebratse (viz., such as have a spine composed 

 of bony blocks, or vertebrae, joined by Hgaments 

 into one flexible rod). For example, that the fore- 

 legs and fore-feet (heads-Umbs of quadrupeds) 

 answer to the arms and hands of a man, to the 

 wings of birds, and to the pectoral fins of fishes. 



* Comparative anatomists have shown the propriety of the name 

 " Head-limbs" by tracing analogues of the shoulder-blades in some of 

 the lower animals (as fishes &c.,) in actual and close attachment to the 

 head. 



