Comparative.] A' N A 
fition of thefe creatures, If all the inteftines were not co¬ 
vered, there would be no favourable derivation of the 
fluid to the guts lying in the poftcrior part of the abdo¬ 
men, which i's the higheft; and befides, had the omentum- 
reached much farther down in us, it would not only have 
fupplied too great a quantity of oil to the lower part of 
the abdomen, but we (liould have been in continual dan¬ 
ger of herniae; and even at prefent the omentum fre¬ 
quently pall'es down with fome of the other vifcera, and 
forms part of thefe tumours. To thefe, however, the 
dog is not fubjedl, as his vifcera do not prefs fo much on 
the 5 rings of the abdominal mufcles, and befides are pre¬ 
vented from palling through by a pendulous flap of fat. 
The inferior and anterior lamella of the omentum is fixed 
to the fpleen, fundus of the ftomach, pylorus, liver, &c. 
in the fame way as the human; but the fuperior, having 
no colon to pafs over, goes direftly to the back-bone. 
This ferves to explain the formation of the fmall omen¬ 
tum in the human body ; which is nothing but the large 
omentum, having loft its fat, paftingover the ftomach and 
colon, where it re-affumes its pinguedo, fo proceeds, and 
is firmly attached to the liver, fpine, &c. 
This animal’s ftomach, though refembling the human 
in its fliape, is fomewhat differently fituated. It lies more 
longitudinal, as indeed all the other vifcera do, to accom¬ 
modate themfelves to the fhape of the cavity in which 
they are contained; that i9, its inferior orifice is much 
farther down with refpedl to the fuperior than the human : 
by this means the grofs food has an eafier paflage into the 
duodenum. Again, the fundus of the human ftomach, 
when diftended, ftands almoft diredtly forwards, which is 
occafioned by the little omentum tying it fo dofe down 
to the back-bone, Sec. at its two orifices ; but, it not being 
fixed in that manner in the dog, the fundus remains al¬ 
ways pofterior: this alfo anfwers very well the fliape of 
the different cavities, the diftance between the cardia and 
fundus being greater than that between the two tides. It 
feems to be much larger in proportion to the bulk of the 
animal than the human, that it might contain a greater 
quantity of food at once ; which was very neceffary, tince 
this animal cannot at any time get its fuftenance as men 
do. The turbilion is not fo large, nor is there any coarc- 
tion forming the antrum Willefii, as in the ftomach of man. 
It is contiderably thicker and more mufcular than ours, 
for breaking the cohefion of their food, which they lwal- 
low without fufficient chewing. Hence it is evident the 
force of the ftomach is not fo great as fome anatomifts 
would have it, nor its contraction fo violent; otherwife 
that of dogs would be undoubtedly wounded by the ftiarp 
bones, &c. which they frequently fwallow ; for the con¬ 
traction is (till greater than in the human ftomach, which 
is much thinner. The rugae of the tunica villofa are 
neither fo large, nor fituated tranfverfely, as in the hu¬ 
man, but go from one orifice to the other: the reafon of 
which difference is, perhaps, that they might be in Id’s 
danger of being hurt by the hard fubftances this creature 
frequently feeds on; and for the lame reafon there is not 
the like coardlion at their pylorus. 
The inteftines of this animal are proportionally much 
ftiorter than ours; for the food which thefe creatures meft- 
ly ufe, foon diffolves, and then putrefies; on which ac¬ 
count there was no occafion for a long tra£I of inteftines; 
the food being required to be quickly thrown out of the 
body. The fame is to be obferved of all the carnivorous 
animals. The mufcular coat of the inteftines is alfo thick¬ 
er and ftronger than the human, to protrude the contents 
quickly and accurately. The valvulse conniventes are lefs 
numerous, and in a longitudinal direftion; and the whole 
traCt of the alimentary canal is covered with a flime, which 
lubricates the inteftines, faves them from the acrimony of 
the excrementitious part, and facilitates its paflage. 
The duodenum differs contiderably in its fituation from 
the human. For in man it firft mounts from the pylorus 
upwards, backwards, and to the right fide; then paffes 
down by the gall-bladder; and, going over the right kid- 
Voii, I. No. 41. 
- O M Y. 4 653 
ney and fuperior part of the pfoas mufcles, makes a cur¬ 
vature upwards; and paffes over the back-bone and vena 
cava inferior, to the left hypochondrium, where it gets 
through the omentum, mefentery, and mefocolon, to com-_ 
mence jejunum , being firmly tied down all the way, the 
biliary and pancreatic ducts entering at its mold depending 
part. Whereas in the dog, the duodenum is fixed at the 
pylorus to the concave furface of the liver, and hangs 
loole and pendulous with the mefentery backvvards into 
the cavity of the abdomen; then turning up again, is fix¬ 
ed to the back-bone, where it ends in the jejunum; the 
bile and pancreatic juice are poured into it at the moft de¬ 
pending part. Therefore the fame intention feems to 
have been had in view in the formation of this part in 
both, viz. the giving the chyle, after the liquors of the 
liver and pancreas are poured into it, a difadvantageous 
courfe, that fo it might be the more intimately blended 
with the humours before its entry into the jejunum, where 
the lafteals are very numerous. And thus, by reafon of 
their different pofture, the fame defign (though by a very 
different order, of the parts) is brought about in both. 
The other fmall guts are much the fame with ours, on¬ 
ly fhorter. The great guts are alfo lhorter and lefs capa¬ 
cious than in the human body; and we take it for a gene¬ 
ral rule, that all animals that live on vegetable food have 
not only their fmall guts confiderably longer, but alfo their 
great guts more capacious, than fuch creatures as feed on 
other animals. Hence man, from this form of his intef¬ 
tines, and that of the teeth, feems to have been originally 
deligned for feeding on vegetables chiefly ; and (till the 
moft of his food, and all his drink, Is of that clafs. The 
reafon of this difference feems to be, that as animal food 
is not only much more ealily reduced into chyle, but alfo 
more prone to putrefaction, too long a remora of the 
juices might occafion the worft confequences. So it was 
neceffary that their receptacles fhould not be too capaci¬ 
ous; but, on the contrary, being ftiort and narrow, might 
conduce to the feafonable difeharge of their contents. 
Whereas, vegetable food being more difficultly dilfolvcd 
and converted into an animal nature, there was a necefiity 
for fuch creatures as fed on it to be provided with a long 
inteftinal canal, that this food in its paflage might be con¬ 
fiderably retarded, and have time to change its indoles in¬ 
to one more agreeable to our nature. 
The appendix vermiformis juftly enough deferves the 
name of an intejlinum caecum in this fubjeti, though, in the 
human body it does not; and it has probably been from 
the largenefs of this part, in this and fome .other animals, 
that the oldeft anatomifts came to reckon that fmall ap- 
pendicle in man one of the great guts. On its internal 
furface we obferve a great number of mucous glands. 
As all thefe throw out flime, their principal office would 
feem to be the procuring a fufficient quantity of that 
matter for the purpofes above-mentioned. Still, however, 
there feems to be fome unknown ufe for this organ in other 
animals; for the appendicula vermiformis in them is ei¬ 
ther of great fize or of great length. In a rat, it is ra¬ 
ther larger than the ftomach; in others, as fwine, and 
fome of the animals which live on vegetables, it has long 
convolutions, fo that the food tr.uft be lodged in it for a 
long time. Thus, probably, fome change takes place in 
the food, which requires a confiderable time to eftedfuate, 
and, though unknown to us, may anfwer very ufeful pur¬ 
pofes to the animal. 
The colon, in the dog, has no longitudinal ligaments; 
and confequently this gut is not purled up in different bags 
or cells as the human : nor does this inteftine make any 
circular turn round the abdomen ; but pall'es diredtly acrofs 
it to the top of the os facrum, where it gets the name of 
reElum. 
The mefentery is confiderably longer than in the human 
body; that, in his horizontal fituation, the inteftines may 
reft fecurely on the foft cufhion of the abdominal mufcles. 
The fat is here difpofed in the fame way, and for the fame 
reafon, as in the omentum. The interftices between the 
8 D fat 
