394 INTRODUCTION TO ZOOLOGY. 



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

 representations here given of the skulls and teeth of three 

 of the most common quadrupeds, and he will at once he struck 

 with the diversity of form and arrangements they exhibit, 

 and the modifications of internal structure they indicate. 



Fig. 299. SKULL OF A HORSE. 



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

 this matter should he 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 establish the unity of plan evinced 

 by their organization. The geologist, in bringing to light the 

 remains of the animals that in former ages were monarchs 

 of the earth, adduces amid all their diversity of form, no 

 example that is not in accordance 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 more potent than the 

 " open sesame' 7 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 



