EVIDENCE FURNISHED BY SCIENCE OF LIKENESSES. 135 



foreign to the reptile class. The boxlike body of the animal is, in 

 short, formed by so much of its skeleton, and by so many of its scales, 

 altered and modified to suit the animal's way of life. It presents 

 us, thus, with no new thing in the way of stnicture, but with an 

 elaboration of the common elements of the reptile body. 



More interesting, perhaps, because more complex in their re- 

 lations, are the changes which occur in the lower jaw and ear, as we 

 ascend from the fishes as the lowest vertebrates to Man and 

 quadrupeds as the highest. We could not find a better example of 

 the manner in which Nature moulds the same elements into widely 

 different forms than the latter subject. Homology teaches us clearly 

 enough that in the elaboration of the skull, as in the modification of 

 the tortoise- skeleton as a whole, new parts and new organs are evolved 

 simply and for the most part by the alteration and higher develop- 

 ment of the original type. When we examine the lower jaw and 

 its connections with the skull in any vertebrate animal below the 

 rank of the quadruped, we find that the jaw is attached to the skull 

 by the intervention of a special bone called the "quadrate bone." 

 The manner in which lower jaw and skull are connected in Man 

 and quadrupeds is very different from the latter arrangement. In 

 Man, as every one knows, the lower jaw works upon the skull directly 

 and of itself, and the " quadrate bone," which one sees so distinctly in 

 the reptile, bird, frog, or fish, is apparently wanting in higher verte- 

 brate life. Is the skull of the quadruped, then, modelled,, as regards 

 its lower jaw and articulations thereof, on a different type from that 

 seen in the lower vertebrate? Comparative anatomy supplies the 

 answer in a highly interesting fashion. 



Attend for a moment to the disposition of the parts of the 

 internal ear, which in quadrupeds we find to exist within the 

 skull and just above the lower jaw. We find three small bones 

 (Fig. 6 1, A, m, /, c,) to connect the "drum" of the ear with the 

 internal hearing apparatus. Of these three bones, one shaped 

 somewhat like a hammer is named, the mal/eus (m\ and to this 



FIG. 61. JAWS OF VERTEBRATA. A,. Quadruped ; B, Lizard; C,' Fish; 



bone our attention must be specially directed. For when we trace 

 this bone downwards through the reptiles and birds towards the 

 fishes, we discover that it alters its relations to the ear and assumes 

 new ones with the lower jaw. In reptiles- and birds, for example, we 



