62 PHILOSOPHY OF ZOOLOGY. 



torpid, than in others. He supposes, that, in consequence 

 of this arrangement, there is only as much blood transmit- 

 ted to the brain during summer as is necessary to excite 

 that organ to action. In winter, when the circulation is slow, 

 the small quantity of blood transmitted to the brain is in- 

 adequate to produce the effect. This circumstance, acting 

 along with a reduced temperature and an empty stomach, 

 he considers as the cause of torpidity. By analogy, he 

 infers, that the same cause operates in producing torpidi- 

 ty with all the other hybernating animals of the other 



Mr CARLISLE, in his Croonian Lecture on Muscular 

 Motion, asserts, that " 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 animals not having this peculiar 

 habit. In all the hybernating mammalia there is a pecu- 

 liar structure of the heart and its principal veins : the supe- 

 rior 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 *." 



We cannot refrain from observing, that these general 

 views do not appear to be the result of a patient investiga- 

 tion of a number of different kinds of torpid animals, but 

 a premature attempt to theorise from a few insulated par- 

 ticulars. Passing, therefore, from these attempts of the 

 anatomist to illustrate the phenomena in question, let us 



* Phil, Trans. 1805, p, 17, 



