Xect. III.] CROCODILE, BIRD, AND OPOSSUM. 77 



region, which forms the rudiment of the excavated part 

 that enlarges the drum cavity on its inner side, is 

 developed in the same manner in all the three types. 

 There is much difference in detail, but the mode of 

 growth, as well as the primordial condition, is alike in 

 all these — Crocodile, Bird, and Opossum. 



Nature, who has framed strange fellows in her time, 

 must have gone to the limits of her power in growing a 

 Crocodile, a Nightingale, and an Opossum out of germs 

 as like to each other as the right hand is to the left. 

 These forms had, undoubtedly, an hereditary some- 

 thing in them that determined each along its own 

 diverging line. The angle of divergence is very acute, 

 but ultimately the distance has become wide enough. 



Character 5. — This character, the entrance of the 

 internal carotid artery through the substance of the 

 basi-sphenoid, seems at first sight to l^e a very little 

 matter. It is, however, a character correlated with a 

 lesser brain and a lower intelligence than we find in the 

 better sorts of the Eutheria. I see an approach to this 

 state of things in the little Ant-eater, a very ancient 

 kind of creature, of a very non-intelligent sort. 



No doubt, if anyone w^ould carefully give himself up 

 to the investigation of the modes of arterial supply, he 

 would find that there is a most orderly series of changes 

 in the development and distribution of these vessels, 

 and of all the arteries in the body. But the interest 

 attached to those which go to form the " circle of AYillis " 



