4 ON THE SKELETON. 



because the head will not be adapted for the progressive motion of the 

 animal, as in fish : the organ of smell is not so large, and mastication 

 is not carried on in the head, as in quadrupeds. 



Pishes have fewer and smaller bones than any other animal, and, 

 except the bones of the spine and head (but what we call head, is head, 

 mouth, lungs, and thorax), the others bear no sort of proportion to the 

 size of body. 



The reason of this is very evident ; first, they have no extremities ; 

 secondly, the ribs in most of them have no motion for respiration, so 

 that they only serve for fixed points for muscles for the motion of the 

 trunk, independently of respiration ; and, thirdly, the body does not 

 require that support which it does in land-animals, because sea-animals 

 float in a medium of the same gravity with their bodies : the blubber 

 [Medusa] is an instance of this. A body will float easily in water, 

 or a fluid nearly of its specific gravity, without the assistance of bones, 

 which would collapse in air ; so that the ribs of fishes that breathe are 

 smaller in proportion. However, the spine is much larger in fishes than 

 in any other animal. This does not seem to be for the support of the 

 soft parts, as many fishes have no spine [i. e. no ossified vertebrae], 

 but for the progressive motion and quick turns of the animal ; for the 

 body is the chief cause of its own motion, therefore requires a strong 

 centre-pin to regulate all its motions. But, upon the whole, I should 

 suppose that there was not so much bony matter in a fish as in a qua- 

 druped. The cetaceous fishes would seem to grow to the largest size 

 of any animal : the shark comes nearest [to them] 1 , 



From what has been said of the bones of fishes, we may see that 

 quadrupeds have more in number, and the reason is that their progress- 

 ive motion is different. The motion of their body contributes little to 

 it, therefore they are obliged to have parts for this purpose, whose 

 strength is to counterbalance the different specific gravity between 

 animals and air — the medium they move in. If an animal were light 

 as air, there would be no occasion for legs. As quadrupeds move in a 

 medium much more rare than themselves, and therefore have a greater 

 tendency to the earth, and likewise to themselves, it was necessary to 

 have bones or hard parts to support each part, so as to overcome this 

 attracting power. The solidity of the earth in some measure compen- 

 sates for the rareness of the air. However, many of the bones of the 

 quadruped that are in some measure similar to those of the fish, are 

 smaller in proportion. The spine of the quadruped has nothing to do 



1 [The basking-shark ( Selache maxima, Cuv.) has been captured in the British 

 channel 36 feet in length ; fossil teeth of the Carckarodon from the ' Red Crag' of 

 Suffolk indicate individuals of this extinct shark of 60 feet in length.] 



