Comparative,] 
wards; whence it would at fird view appear, that their 
: heads would be ere£t, and their pofterior parts mod de¬ 
pending when railed in the air : but by ftretchingout their 
heads, which aft upon the lever of a long neck, they alter 
their centre of gravity contiderably; and alfo by filling 
the lacs or bladders in the in fide of their abdomen with 
air, and expanding their tail, they come to make the 
pofterior part of their bodies confiderably higher ; and 
thus they fly with their bodies nearly in an horizontal li- 
tuation. Hence we find, that if their necks are kept from 
being ftretched out, or their tails cut away, they become 
incapable of flying any confiderable diftance. The large- 
'nefs of the wings in different fowls varies according to the 
-occalions of the creature. Thus birds of prey, who mull 
fly a confiderable way to provide their food, have large 
Uxong wings; whereas domeftic birds, who find their nou- 
fllhment almoft every where, have very Ihort and but 
fmall wings. 
Carnivorous animals are provided with ftrong crooked 
claws for catching their prey: water-fowls ufe them for 
fwimining; and, principally for this purpofe, have a ftrong 
firm membrane interpoled between the toes. There is a 
beautiful mcchanifm to be obferved in the toes of fowls, 
which is of confiderable ufe to them. For their toes are 
naturally drawn together, or bent, when the foot is bent: 
this is owing to the Ihortnefs of the tendons that pafs over 
them, which is analogous to our heel: and that the toes 
are let in the circumference of a circle, as our fingers are : 
hence, when the foot is bent, the tendons mult conlequent- 
ly be much ftretched; and, fince they are inferted into the 
toes, muft of necefiity bend them when the foot is bent; 
and, when the foot is extended, the flexors of the toes are 
again relaxed, and the toes therefore expanded. This is 
alfo of great ufe to different kinds of fowls; thus the hawk, 
defcending with his legs and feet extended, fpreads his ta¬ 
lons over his prey; and, the weight of his body bending 
his feet, the toes are contrafted, and the prey is feized by 
the talons. This is alfo of great ufe to water-fowls; for, 
had there been no fuch contrivance as this, they muft have 
Igft as much way when they pulled their legs in as they 
had gained by the former ftroke ; but, as the parts are 
now framed, whenever the creature draws in its foot, the 
toes are at the fame time bent and contraited into lefs 
fpace, fo that the refiftance made againft the water is not 
near fo great as before; on the contrary, when they ftretch 
their foot, their toes are extended, the membrane between 
them expanded, and confequently a greater refiftance made 
to the water. Again, fuch fowls as live moftly in the air, 
or have occalion to fuftain theml'elves on branches of trees 
in windy weather, and even'in the night-time whenallcep, 
while all their mufcles are fuppofed to be in a ftate of re¬ 
laxation; fuch have no more to do but lean down the 
weight of their bodies, and their toes continue bent with¬ 
out any nnifcles being in aftion ; and whenever they would 
difentangle themfelves, they raife up their bodies, by which 
their foot, and confequently their toes, are extended. 
The roftrum, bill, or beak, of fowls, is compofed of two 
mandibulae, and, as in quadrupeds, the upper one has no 
motion but what it pofieffes in common with the head. 
But parrots are an exception to this rule; for they can 
move the upper mandible at pleafure : this is exceedingly 
convenient, as it enables them to lay hold of whatever 
comes in their way. Carnivorous fowls have their beaks 
long, fharp, and crooked ; domeftic fowls, fuch as the hen 
kind, See. have ftrong ihort beaks, commodiouily fitted to 
dig up and break their food ; the water-fowls, again, have 
long, or very broad fcoop-like beaks, which is moll conve¬ 
nient for them. The fternum of fowls is much larger pro¬ 
portionally than the human, and has a ridge riling in its 
middle for the more commodious origin of the mufcles 
that move the wings. It is alfo lefs moveable than ours; 
for, had it been very moveable, a great deal of the for,ce 
employed for moving the wings would at every contraftion 
of the mufcles have been loft, or eife feme other mufcles 
muft have come in play to keep the fternum firm; but 
Vol. 1 . No, 42. 
661 
this additional weight would have been inconvenient for 
their progrefiion. 
ANATOMY of a COCK. 
Though this kind of birds lives upon food -fomewhat 
fimilar to that of man, yet, as they have no teeth to fepa- 
rate or break down this food, we Ihould expeft to find 
fomething to compenfate. the want of teeth, fomethrng 
remarkable in tine organs of digeftion: we (hall there¬ 
fore begin with thefe parts. The ccfophagvs of the cock 
runs down its neck, fomewhat inclined to the right lide ; 
and terminates in a large membranous lac, which is the 
Lngluvies or- crop, where the food is macerated and dif- 
foived by a liquor feparated by the glands, which arc eafily 
obferved every where on the internal furface of this'bag. 
The eft'eft of this maceration may be very well obferved in 
pigeons, who are fornetimes in danger of being fuft'oeated 
by the peafe, See. they feed upon, (welling to fuch an inn- 
nnenle buik in their ingluvies, that they can neither get 
upwards nor downwards. If it be a favourite fowl, it 
might be preferved by opening the fac, taking out the 
peafe, and fewing up the wound. The food, getting out 
of this fac, goes down by the remaining part of the cefo- 
phagus into the vmtriciilus fuccenturialus , or infundibulum 
Peycri, which feems to be a continuation of the gullet: it 
has feveral glands, for feparating a liquor to dilute the 
food (till more before it comes into the true ftomach or 
gizzard, ventriculus callofus. The gizzard confifts of two 
very ftrong mufcles, covered externally w ith a tendinous 
aponeurofis, and lined on the inlide by a very thick firm, 
membrane, which we evidently difeover to be a produc¬ 
tion of the cuticula. This might have been proved ia 
fome meafure a priori , from obferving, that this mem¬ 
brane, which in chicks is only a thin, (light pellicle, by 
degrees turns thicker and firgnger the more attrition it 
fullers: but there is no other animal fubftance, fo far as 
we know', which grows more hard and thick by being (ob¬ 
jected to attrition, except the cuticula. Hence may be 
draw n forne kind of proof of what has been affirmed con¬ 
cerning the tunica villofa of the ftomach and inteftines ia 
the hitman body, viz. that it was in part a continuation of 
the epidermis ; nay, all the hollow parts of the body, even 
arteries, veins, &c. feem to be lined with a produftion of 
this membrane, or one analogous to it. The ufe of the in¬ 
ternal coat of the ftomach of fowls, is to defend the more 
tender parts of that vifeus from the hard grains and little 
ftones thefe creatures fvyallow. The ufe of the gizzard is 
to compenfate for the want of teeth ; and it is well fitted 
for this purpofe from the great ftrength it poileffes. 
The digeftion of thefe animals is performed merely by 
attrition, as is evinced by many experiments ; and it i «5 
further affifted by the hard bodies they fwallow. We fee. 
them daily take down confiderable numbers of the molt 
folid little rugged flints they find ; and thefe can ferve for 
no other purpofe than to help the trituration of their ali¬ 
ments. After thefe pebbles, by becoming fmooth, are 
unfit for this office, they are thrown up by the mouth. 
Hence fowls that are long confined, though ever fo well 
fed, turn lean for want of tilde ftones to help their digef¬ 
tion. But this was put beyond all difpute by Mr. Tauvry, 
who gave a piece of metal to an oftrich, convex on one 
(ide, and concave on the other, but carved on both; and, 
opening the creature’s body fome time after, it was found, 
that the carving on the convex (ide was all obliterated, 
while the engraved charafter remained the fame as before, 
on the concave fide, which was not fubjefted to the (to- 
mach’s prcft’ure: this circumftance could not have hap - 
pened had digeftion been performed by a menftruum, or 
any other way whatfoever; but may be eafily (dived by 
allowing a (irnple mechanical prelfure to take place. We 
are, however, by no means to conclude from this, as fome 
have too raflily done, that in the human body digeftion is 
performed by fimple attrition; othervvife we may, with 
equal ftrength of reafon, by as good arguments drawn, from 
what is obferved in fifties, prove that the aliments are dif- 
8 F folveti 
ANATOMY. 
