OF THE SPERM WHALE. 
89 
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 inserted into 
two extremities, as in quadrupeds, 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 structure, 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 un- 
pleasant smell, and is most remarkable in the psose 
muscles and those of the back. 
OF THE CONSTRUCTION OF THE TAIL® 
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 ten- 
dinous 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 composed entirely of tendinous 
fibres passing directly across between the two external 
ones above described, their length being in proportion 
to the thickness of the tail; a structure which gives 
