41 



with the generality of mankind as the science of 

 unity of organic structure is at present; and 

 what has not the former doctrine, assiduously 

 prosecuted, done for chemistry ? It has con- 

 verted it, from a vague and unsatisfactory state- 

 ment of isolated facts, into a certain, a consistent, 

 and a determinate science ; and why may we 

 not hope, that the prosecution of the study in 

 question may do as much for anatomy, and teach 

 us not to be satisfied with knowing merely what 

 is the structure of each organ, unless we can 

 explain also why it has that structure, and why 

 it could not, consistently with certain established 

 laws, have had any other ? 



" All nature is but art unknown to thee ; 



All chance, direction which thou canst not see." 



It is only, however, as I have already observed, 

 when we take a full survey of the whole of ani- 

 mated nature, and observe the strict analogies 

 between certain organs in each of the various 

 tribes of animals, as we rise progressively in the 

 scale of creation to man, that we are struck with 

 the analogies which these same organs, as oc- 

 curing in the human body, also offer. No two 

 things, for instance, seem to be more unlike than 

 one of the vertebrse and the posterior bone of 

 the skull in the human skeleton ; but in some 

 fishes they are nearly entirely the same, and the 

 gradations in both, from a fish to man, are al- 

 most insensible. So also the similarity between 

 the ribs and either the lower jaw, on the one 



