APPENDIX. 527 



the moving powers should not have, been used in 

 fish, is probably not so easily answered ; but in 

 fish the muscles of the body are of nearly the same 

 length as the vertebrae. 



The depressor muscles of the tail, which are 

 similar in situation to the psose, make two very 

 large ridges on the lower part of the cavity of the 

 belly, rising much higher than the spine, and the 

 lower part of the aorta passes between them. 



These two large muscles, instead of being in- 

 serted into two extremities as in the quadruped, 

 go to the tail, which may be considered in this 

 order of animals as the two posterior extremities 

 united into one. 



Their muscles, a very short time after death, 

 lose their fibrous texture, and become as uniform 

 in texture as clay or dough, and even softer. 

 This change is not from putrefaction, as they 

 continue to be free from any offensive smell, and 

 is most remarkable in the pso^e muscles, and those 

 of the back. 



The mode in which the tail is constructed is 

 perhaps as beautiful, as to the mechanism, as any 

 part of the animal. It is wholly composed of 

 three layers of tendinous fibres, covered by the 

 common cutis and cuticle : two of these layers are 

 external; the other internal. The direction of 

 the fibres of the external layers is the same as in 

 the tail, forming a stratum about one third of an 

 inch thick ; but varying in this respect as the tail 

 is thicker or thinner. The middle layer is com- 

 posed entirely of tendinous fibres, passing directly 



