554 
WING. 
for migration. That a few instances occur of their having* been found in 
old shafts of mines, and in similar situations, we will not dispute ; though 
it is somewhat extraordinary that those who have stated such as facts, 
do not mention which species of swallow was so found ; nor have we 
been able to find a sing-le person of g-ood authority who ever saw the 
fact. Why these birds should ever have been denied their migrative 
powers, we cannot conceive, when others, much less qualified for long 
flights, have not been doubted. That this bird, as well as the chimney 
swallow, is now and then seen flying about long after the general dis- 
appearance of these birds, we have more than once had ocular proof. 
But these instances must be attributed to some accident or individual 
defect, which prevented them from performing their usual autumnal 
flight. It is well known that in some animals, whose radical heat is sen- 
sibly affected by cold, the power of action is lost when the fluids become 
languid, and animal life is as it were suspended. The bat, the dor- 
mouse, and hedge-hog, become torpid in winter, when the mean state 
of the air is below 45 ° ; and their heat sems to keep pace nearly with 
the state of the atmosphere. But even at this season, the general 
warmth of the sun regenerates their benumbed limbs, and the bat is 
sometimes seen flying about at mid-day, but returns again to its former 
state for weeks, and perhaps months, if the air proves colder. 
Thus it is with the martin and swallow who have been accidentally 
detained in this northern climate ; they are roused by a certain degree 
of heat, and the calls of hunger induce them to fly abroad for food ; and 
it is much to be doubted, whether this sudden return of all the animal 
functions does not prove fatal, from not being able to find sufficient 
food to supply the natural excretions, which in a torpid state have been 
observed to be little or none. It cannot be supposed it was intended by 
nature, that birds, who have the power of shifting their quarters in so 
expeditious a manner, and with such ease, should ever repose during 
the colder season. It is therefore most reasonable to suppose such acci- 
dental migrative birds, who are detained in a climate unsuitable to their 
nature, perish before the return of the warmer months. We have 
known several instances of a single bird of this species, flying about in 
search of food after the middle of November, but never for two days 
together, nor after the latter end of that month. It is found in most parts 
of Europe, and in Asia. 
WING. — * The wing of a bird consists of five principal joints, with 
small auxiliary ones as represented in the annexed figure, and by a com- 
parison with the human arm, or the fore leg of a quadruped, we shall 
find there is considerable similarity. The joints a b and c answer to 
