378 INTEODUCTION TO ZOOLOGY. 



Bearing these facts in mind, let any one but look at the re- 

 presentations here given of the skulls and teeth of three of the 

 most common quadrupeds, and he will at once be struck with 

 the diversity of form and arrangements they exhibit, and the 

 modifications of internal structure they indicate. 



Fig. 300.— Skull of a Horse. 



"We are desirous, even at the risk of some repetition, that 

 this matter should be clearly understood. The researches of 

 the zoologist and the comparative anatomist, have proved the 

 perfect dependence of one part of the animal form upon another. 

 To this there is no exception ; all living beings testify the same 

 truth, and estabUsh the unity of plan evinced by their organiz- 

 ation. The geologist, in bringing to light the remains of the 

 animals that in former ages were monarchs of the earth, adduces, 

 amid aU their diversity of form, no example that is not in ac- 

 cordance with the same great truth. 



Hence, it is obvious that if there are structural laws, to 

 which all are subject, the comparative anatomist may from 

 portions of the frame infer the size, the structure, and the 

 functions of all the rest, and describe the conditions under 

 which the animal had lived. 



To the genius of Cuvier we are indebted for pointing out 

 this mode of investigation, and showing the important results 

 to which it leads. The path which he thus opened has been 

 successfully explored, and has revealed much that was pre- 

 viously unknown. It has brought to light forms and propor- 

 tions too strange for Fancy to imagine, but not for Science to 

 delineate. The fossil bone has in the hands of the zoologist 

 become instinct with life, and told the tale of its existence. It 

 has furnished him with a spell moi*e potent than the " open 

 sesame" of the eastern tale, and unlocked the portals within 

 which the history of a former world lay recorded. 



The necessary dependence of one part of the animal frame 



