65S 
In the fame way, when the retina is inflamed, a great num¬ 
ber of rays of light would occafion a painful fenfation; 
therefore the pupil is contracted : on the contrary, in dy¬ 
ing people, or in a beginning amaurofis, it is generally di¬ 
lated, as the eyes on Inch occafions are very difficultly af¬ 
fected, and as it were infenlible. 
The p'pderior part of the choroid coat, which is called 
tape turn, is of different colours in different creatures. For 
oxen, feeding jnoflly on grafs, have this membrane of a 
green colour, that it may reflect upon the retina all the 
rays of light which come from objects of that colour, 
while other rays are abforbed ; thus the animal lees its 
food better than it does other objeCts. Cats and owls 
have their tapetum of a whitifh colour; and for the fame 
reafons have the pupil very dilatable, and their organs of 
vi/ibn acute. And we fhall find, that all animals fee more 
or leis diltiuCtly in the dark, according as their tapetum 
approaches nearer to a white ot black colour. Thus dogs, 
who have it of a greyilh colour, diltinguilh objects better 
in the night than man, whole tapetum is dark brown, and 
who fees worlt in the dark of any creature. The diffe¬ 
rence then of the colour of the tapetum, as indeed the 
fabric of any other part indifferent creatures, always de¬ 
pends on fome particular advantage accruing to the animal 
in its peculiar manner of life from this Angularity.. 
The brain is proportionally much finaller in all quadru¬ 
peds than the human ; but, as in man, it is divided into ce¬ 
rebrum and cerebellum, and thefe two parts bear nearly 
the fame proportion to one another as in ns. There was 
no occafion for fo great a quantity of brain in thofe ani¬ 
mals as in man : lince in them all its energy is employed in 
their progreflion, while man has a great wade of ipirits 
in the exercife of his reafon and intellectual faculties. 
And, betides tins, a great bulky brain would be inconve¬ 
nient to thefe creatures, inafmuch as it would add confi- 
derably to the weight of the head; which, having the ad¬ 
vantage of a long lever to act with, would require a much 
greater force to fupport it than it now does ; for the heads 
of the greatelt part of quadrupeds are not near fo heavy 
as they would at firlt light leem to be, from the limts fron- 
tales being produced a great way upwards to enlarge the 
organs of fmelling. The pits in the anterior part of their 
ikulls are much more confpicuous than in the human cra¬ 
nium; which may be occalioned by the depending podure 
of thefe creatures heads while they gather their food ; the 
brain at this time gravitating much on the bones while 
they are as yet foft, will gradually make impreilions upon 
them at thefe places where it riles into eminences. This 
is prevented in man molfly by his ereft pofture. The fe- 
coiid procefs of the dura mater , or tentorium cerebellifuper- 
expanfum, is conliderably thicker and ftronger in molt 
quadrupeds than in man ; efpecially in fuch of them as are 
very fwift of foot, as hares and rabbits, and that moft 
when they are old. This membrane is generally oflified, 
or we find the place of it fupplied by a bone, that it may 
the more effectually keep off the fuperincumbent vein 
from the cerebellum in their rapid motions, which other- 
wife would be of bad confequence. 
The olfaCtory nerves are very large, and jultly deferve 
the name of procejfus mamillares. They are hollow, and 
conlilt of a medullary and cineritious fubltance, and at 
firlt fight appear to be the anterior ventricles of the brain 
produced ; but in man they are fmall, and without any 
difcernible cavity. The reafon of this is fufficiently evi¬ 
dent, if we confider how this animal’s head is fituated; 
for the lymph continually graviting upon the inferior part 
of the ventricles, may thus elongate and produce them ; 
but from this very inferior part the olfaftory nerves rife, 
and are fent immediately through the os ethmoides into the 
nofe. Hence the ancients, thinking they were continued 
hollow into the nofe, believed they were the emunCtories 
of tiie brain. In the brain of (heep, which, by its firm 
texture, is the bed fubjeCt of any lor fearching into the 
Itrufclnre of this part, we evidently fee, that the name of 
the figmoid cavity was very properly applied by the ancients 
[Comparative. 
to the lateral ventricles of the brain; which are really of 
a greater extent than they are ordinarily painted by’ the 
anatomills, reaching farther backwards, and forwards 
again under the fubltance of the brain. The cortical and 
medullary parts, as well as the corpus callofum, are firrti- 
lar to.thole parts in man. 
The nates and hjies deferve this name much better here 
than in the human body, with rel'peCt to each other. 
They are larger in the quadruped ; and hence we perceive 
that there is no great reafon for aferibing the different ope- 
rations'to any particular lize or lhapeof thefe parts. They 
are here alfo of different colours: the nates being of the 
colour of the cortical, and the teftes of the medullary, 
fubltance of the brain ; whereas in man they are both of 
one colour. The reafon of thefe differences, and others 
ot the like nature, we fhall not pretend to determine; for 
we have hitherto Inch an imperfefct knowledge of the brain 
itfelt, that we are entirely ignorant of the various ufes of 
its different parts. We may in general conclude, that the 
varying in one animal from what it is in another, is fitted 
to the creature’s particular way of living. 
The rcte mirabile Galeni, fituated on each fide of the fella 
turcica , about which there has been fo much difpute, is 
very remarkable in mod: quadrupeds. This plexus of vef- 
fels is nothing elle than a continuation of the internal ca¬ 
rotid arteries, which, entering the fkull, divide into a vaft 
number of minute branches running along the fide of the 
fella turcica, and, uniting afterwards, are fpent on the 
brain in the common way. Galen feems with jitdice to 
fuppole, that this plexus of velfels ferves for checking the 
impetuofity of the blood dellined for the brain. The 
drudture of the brain differing but very little in all quadru¬ 
peds, it will be needlefs to examine it in any other. 
ANA TO MY of a COW. 
The next fpecies of quadrupeds we propofe to confider, 
is the ruminant kind, of which we have an example in the 
cow ; and accordingly fhall take the foetus of the animal 
in utero, that we may firft remark lome things that are pe¬ 
culiar to it in that date, and afterwards proceed to exa¬ 
mine its vilcera as a ruminant animal. 
The form of a cow’s uterus differs from the human, in 
having two large cornua. This is common to it with other 
brutes ; for a bitch has two long cornua uteri. But thefe 
again differ (as being multiparous and uniparous) in this, 
that in the bitch’s cornua the foetufes are contained; 
whereas here there is only part of the fecundities, being 
modly the allantois with the included liquor. The muf- 
cular fibres of the uterus are more ealily difeovered; its 
internal furface has a great number of fpongy, oblong, 
protuberant, glandular bodies, fixed to it. Thefe are 
compofed of velfels of the uterus terminating here. In an 
impregnated uterus, we can ealily prefs out of them a chy¬ 
lous mucilaginous liquor;-they are compofed of a great 
many proceifes or digituli, and deep caverns, anfwering 
to as many caverns and proceifes of the placenta. Their 
refemblance has occafioned the name of papilla: to be given 
them; and hence it was that Hippocrates was induced to 
believe that the foetus fucked in utero. The papillae are 
found in all the different dages of life, in the various da 
ges of pregnancy, and likewife in the unimpregnated date. 
It is not eafy to determine whether the uterus grows thick¬ 
er or thinner in the time of gedation. The membranes, 
it is plain, (by the dretching of the parts,) mud be made 
thinner; but then it is as evident, that the vellels are at 
that time enlarged, upon which principally the thicknefs 
of any part depends ; fo there feems to be as much gained 
the one way as is loll the other. 
The os uteri is entirely {hut up by a glutinous mucila¬ 
ginous fubltance, that is common to the females of all 
creatures when with young ; by this the external air is ex¬ 
cluded, which would foon make the liquors corrupt; it 
alfo prevents the inflammation of the membranes and the 
hazard of abortion. By this means alfo the lips of the 
womb are kept from growing together, which they woijld 
otherwife 
ANATOMY. 
