on muscular Motion . 
*7 
muscle on the thirteenth. This unsuccessful experiment was 
made with the hope of ascertaining the changes produced in 
water by the respiration of aquatic animals, but the water had 
not undergone any chemical alteration. 
Animals of the class mammalia which hybernate, and become 
torpid in the winter, have at all times a power of subsisting 
under a confined respiration, which would destroy other ani- 
mals not having this peculiar habit. In all the hybernating 
mammalia there is a peculiar structure of the heart, and its 
principal veins ; the superior cava divides into two trunks ; the 
left, passing over the left auricle of the heart, opens into the 
inferior part of the right auricle, near to the entrance of 
the vena cava inferior. The veins usually called azygos, 
accumulate into two trunks, which open each into the branch 
of the vena cava superior, on its own side of the thorax. The 
intercostal arteries and veins in these animals are unusually 
large. 
This tribe of quadrupeds have the habit of rolling up their 
bodies into the form of a ball during ordinary sleep, and they 
invariably assume the same attitude when in the torpid state : 
the limbs are all folded into the hollow made by the bending 
of the body ; the clavicles, or first ribs, and the sternum, are 
pressed against the fore part of the neck, so as to interrupt the 
flow of blood which supplies the head, and to compress the 
trachea: the abdominal viscera, and the hinder limbs are 
pushed against the diaphragm, so as to interrupt its motions, 
and to impede the flow of blood through the large vessels 
which penetrate it, and the longitudinal extension of the cavity 
of the thorax is entirely obstructed. Thus a confined circu- 
lation of the blood is carried on through the heart, probably 
mdcccv. D 
