238 
F A R R I E RY. 
roides, from its refemblance to the chorion, which inclofes 
the foetus in the womb; this rifes from the pia mater, 
and forms the inner coat of the optic nerve. It is black 
on its infide, and open on its fore-part the whole breadth 
of the ptipilla; the fore-part of this coat is alfo diftin- 
guilhed from its back-part, by the name of uvea, from its 
refemblance to a grape. To this belongs the ligamentum 
ciliare, becaufe it confifts of {lender filaments, like the 
hairs of the eye-lid. The ufe of thefe filaments is to 
widen and conltringe the cryfiailine humour, by contract¬ 
ing or opening the perforation of the uvea. The inner- 
mod, or fourt h tiinicle, is an expanfion of the fubftance 
ot the optic nerve, and is called the retina, becaufe it en- 
ccmpafies the vitreous humour likea net ; by a combina¬ 
tion of the rays of light on the fine filaments of this coat, 
and Aie reflection which is caufed by the opaquenefs of 
the 1’clerctica, and blacknefs of the infide of the uvea, all 
external images are conveyed diftinCt to the imagination; 
whereas, if the rays were not thus collected on the retina, 
there could be no fuch thing as diftinct vifion. 
The humours of the eye are in number three. The 
outermoft is called the aqueous, or watery humour, being 
thin and fluid ; it fills up the fpace between the cornea 
and cryfiailine humour in the fore-part of the eye. The 
cryjlalline humour is fo called from its brightnefs, being 
clear and tranfparent, like cryftal ; it is inclol'ed in the 
vitreous humour, and is the chief inftrument whereby 
the rays of light are collected upon the filamentous ex- 
panfipn of the retina: in the largenefs and purity of the 
cryjlalline lens in horfes, conlifis the goodnefs of their 
eyes, which fiiould above all things be regarded ; and it 
is this valuable acquifition which gives him a fuperioiity 
over man, when travelling in the dark. The laft is cal¬ 
led the vitreous humour ; it is not fo folid as the cryfiailine, 
hut exceeds both it and the watery humour in quantity ; 
it is partly convex, excepting that cavity where it receives 
and (urrounds the cryfiailine. It is not fo bright as the 
cryfiailine, but yet tranfparent, that the vilible fpecies 
received into the cryfiailine humour might not be reflect¬ 
ed before tiiey reach the retina, but be tranfmitred to it 
pure and unmixed. 
The par. s within the mouth are the palate, uvula, and 
glands, (called the almonds of the ears), the tongue, and 
its muffles. The palate, fo called from its being fenced 
or paled in with teeth, forms the upper part of the mouth ; 
it extends from the back part of the mouth to the fore¬ 
teeth, but is not fo hollow in a horfe as in human fubjeCts ; 
it is compofed of eighteen bars, or rugm, and confifts of 
bones and peculiar glanduldus flefti which are covered 
with a thick coat, full of perforations, that afford a paf- 
fage to the faliva, which is feparated from the glands 
above-mentioned ; fee the palate, as placed in the mouth, 
in the Farriery Plate IV. at fig. 8. The uvula is a red 
fungous kernel, fomewhat long, feated at the back part 
of the palate, where the internal pafiage of the nofe opens 
into the mouth, hanging downward, with a fmall obtufe 
end over the chink of the larynx, as fhewn at fig. io, in 
the above-mentioned engraving. The ufe of the uvula is 
to moderate the coldnefs of the air before it paftes into 
tlie lungs, and to hinder'any thing from falling into the 
windpipe. In a horfe it is of further ufe, as it hinders 
the water from going into the nofe when he drinks. 
The tongue is of a flefhy fubftance, having veffels of all 
forts, viz. veins from an inward branch of the external 
jugulars, arteries from the carotids, and nerves from the 
fifth and ninth pair. Underneath the root of the tongue 
is a large gland, from whence two pipes, called the Jali- 
vqry dulls, fpring, one from the fore and the other from the 
hind part; -thele two are loon united into one, which runs 
toward the chin ; as delineated in the Farriery Plate VII. 
fig. 6. In a horfe there are other remarkable glands that 
hand on each fide thisduCI, and difeharge themfelves into 
it. This pipe ends in other fmall glands toward the 
fraenum, or bridle of the tongue, which difeharge part of 
the faliva that keeps the mouth continually moift. Be- 
fides this duCt, there are two others of the fame ufe, which 
rife out-of the glands under the ear, called the parotides, 
and run on the outfide of the jaw-bone to the middle of 
the check, where they open into the mouth. For this 
gland, fee the Farriery Plate VII. fig. 5 ; and for the pro¬ 
perties and office of the glands in general, lee Anatomy, 
vol. i. p. 527. 
The annexed Farriery Plate VIIT. exhibits the internal 
parts proper to the bend, as deferibed above. Fig. j, 
(hews the natural poiition of the brain in the (kull : a, 
the brain j. b, the hind part of the brain. Fig. 2, a lon¬ 
gitudinal feCtion ot the brain : a, the cortical fubftance ; 
b, the medullary fubftance ; c, the fornix or arch, with 
its fupporters ; d, beds of the optic nerves; e, anterior 
ventricle ; ./, glans pinealis ; g, the teftes ; h, the nates ; 
z, the infundibulum ; k, the cortical fubftance ; /, the 
arbor vitae ; m, the medullary fubftance ; n, communica¬ 
tion from the third to the fourth ventricle ; 0, the fpinal 
marrow. Fig. 3, a view of the brain, from the fide of the 
bottom of the cranium : a, the olfaCtory nerves; b, the 
optic nerves. Fig. 4, ereCt view of the globe of the 
eye, with the optic nerve. Fig. 5, interior conftruCtion 
of the uvea. Fig. 6, the cryfiailine lens. Fig. 7, repre- 
fents a vertical feCtion the head, to demonfirate the ac¬ 
tion of deglutition : a, the tongue cut vertically ; b, vela 
palatini, under and between which and the tongue Hides 
the food, to fall into the pharynx ; c, the trachea, or 
wind-pipe ; d, thejpharynx, oropeninginto theoefophagus. 
Of the THORAX, or CHEST. 
The thorax, or cheft, is formed fuperiorly, by the 
dorfal verterbrx ; inferiorly, by the fternum or breaft 
bone, and enfiform cartilage ; laterally, by the ribs; and 
pofteriorly, it is bounded by the diaphram or midriff. 
In figure it is rather conical, with its bale or largeft part 
towards the abdomen, and its apex oppofed to the neck. 
It is proportionably much fmalier than the human! and 
differing conliderably in form, being very much contracted 
at its lower part.near the fternum. The internal connec¬ 
tion formed between the head and the thorax, is by means 
of the trachea or wind-pipe, which is a cylindrical carti¬ 
laginous tube, extending from the throat to the cheft. 
This organ is not made up of one entire cartilage, but of 
feveral cartilaginous rings, which are united by ftrong 
membranes ; and fuch is the elafticity of thefe cartilages, 
that the tube is enabled to preferve its cylindrical form, 
even when it receives conliderable prelfure, and thereby 
affords free ingfefs and egrefs to the air in refpiratic-n. 
The upper part of the trachea is compofed of ftronger 
cartilages than the other parts of the tube, and is termed 
larynx ; to this is connected a ftrong valve, called epiglottis, 
which is always open, except in the aft of ( wallowing ; it 
is then forced down upon the larynx, fo as to prevent 
food, or any thing which may be pafiing over the throat, 
from falling into the wind-pipe. See the trachea, or wind¬ 
pipe, as connected with the head and cheft, in the Farriery 
Plates IV. and VII. Where the trachea joins the cheft, 
it divides into numerous branches, which, gradually be¬ 
coming fmalier, at length terminate in minute cells. 
The cavity of the cheft is not at all times of equal 
magnitude ; being alternately larger and fmalier. This 
dilatation and contraction, is for the receptionand expul- 
(ion of air; and is performed by means of in(ercoftal 
mufcles, which draw the ribs forward, and dilate the 
cheft from fide to fide. The diaphram allilts likewife 
by preiling the contents of the belly backwards, thereby 
enlarging the cavity. The cefihtion of thefe aCtions, 
produces the return of the cavity to its original fize. The 
reception of air into the cheft during its enlargement, is 
termed infpiration ; and its expulfion on its contraction, 
cxjpiration ; which aCtions form the function we call re- 
Jpiration , which lee fully explained under Anatomy, 
vol. i. p. 611. 
On opening the cheft, there appears a fmooth polhhed 
membrane, called the pleura, attached to its upper lurface, 
a This 
