eyas 
Il.t . Unfledged. 
* hauke up mounts unto the skies, 
His newly-budded pineons to assay. 
^,,-nxer, F. Q., I. xi. 34. 
Ere flitting Time could wag his eyas wings. 
Spenser, Hymn of Heavenly Love, 1. 24. 
eyas-muskett (ras-rnus // ket), . 1. A young 
unfledged male hawk of the musket kind, or 
sparrow-hawk. 2. Figuratively, a pet term 
for a young child. 
Mrs. Page. Here comes little Robin. 
Mrs Ford How now, my eyas-musket ! What news with 
you? Shale., M. W. of W., iii. 3. 
eydent (a'dent), a. Same as ithand. 
eye 1 (I), ; pi- eyes (Iz), obsolete or archaic eyen, 
<-i/m: [Early mod. E. also eie; < ME. eye, eghc, 
eighe, ege, eie, ehe, ee, etc., pi. eyen, eghen, eigh- 
eu, egen, eien, eene, ein, iyen, ine, etc., also later 
eyes, etc., < AS. edge, pi. cdgan = OS. oga = 
OFries. age, oge = MLG. LG. oge = D. oog = 
OHG. ouga, MHG. ouge, G. auge = Icel. auga = 
OSw. auga, Sw. oga = Dan. die = Goth, auqo, 
eye. The Teut. forms do not quite agree with 
the other Aryan forms, which are somewhat ir- 
regular: L. oculus (> It. occhio = Sp. ojo = Pg. 
olho = Pr. olh = F. ceil: see ceiliad, eyelet, ocu- 
lar, etc.), dim. of an assumed "ocus; = Gr. oaae, 
dual of an assumed *daoof for "onyof (&KKO( in 
Hesychius) (cf. Boeotian 6/cra/Mof or oKKaMof, 
reg. Gr. oj>8a^6f, eye) ; = OBulg. Bulg. Serv. Bo- 
hem. Pol. oko = OPruss. agins Lith. akis = 
Lett, acs = Skt. akshan, eye; appar. from tlie 
root (Gr. *6/c, *6;r) of Gr. oaaeoBai, see ; ot^eaOat. 
fut. associated with opav, see, oiraira, I have 
seen, oirn/co'f, pertaining to sight, 'cmrrjp, one 
who sees, oi/j (OTT-), aty (UJT-), the eye, coun- 
tenance, etc. ; cf . Skt. y iksh, see. The word 
eye appears disguised in dais-y and wind-ow, 
q. v. See ocular, etc., ophthalmia, etc., optic, 
etc.] 1 . The organ of vision ; the physiological 
mechanism of the sense of sight ; an anatomi- 
cal arrangement of parts by which optical im- 
ages may be formed; in general, any part of 
an animal body by means of which the faculty 
of vision is exercised, or the impact of the light- 
rays is sensed as a visual impression or optical 
image. In most of the higher animals, as nearly all ver- 
tebrates, the eye is developed as a very special sense-organ 
of great structural complexity and functional delicacy. 
But from the point of view of comparative anatomy an 
eye is any part of an animal body which responds more 
readily than other parts to the special stimulus of light, 
or whose activity is specially excited by the impact of 
light-rays. Thus, an extremely rude eye in the form of a 
mere spot, often a pigment-spot sensitive to light, is com- 
mon in low animals, as in infusorians, and may be situ- 
ated anywhere on the body, and may be indefinitely mul- 
tiplied in number. These rudiments of eyes are commonly 
described as eye-specks, eye-points, or eye-spots. (See cut 
under Balanoglossus.) In various ccelenterates and echi- 
noderms organs apparently responsive to the action of 
light occur in various parts of the body and in varying 
numbers. Somewhat higher in the scale of evolution, 
eyes become unmistakable in structural character, how- 
ever dim or uncertain their actual visual function may be, 
as in worms, snails, etc. But in some of the Mollusca, as 
cuttlefishes, eyes are highly specialized as visual organs of 
conspicuous character, comparable to those of vertebrates, 
though constructed on a different plan. In the vast as- 
semblage of arthropods, as crustaceans, insects proper, 
and arachnidans, constituting a large majority of the ani- 
mal kingdom, eyes as a rule are well developed under one 
or both of two main modifications, namely, the simple eye 
or ocellus and the compound eye or oculus. (See compound 
eye, below, and cut under falx.) Such eyes are usually 
only two, but may be four, six, or eight in number. These 
higher numbers of eyes occur chiefly in arachnidans, as 
spiders. Crustaceans have normally a single pair, often 
mounted on movable eye-stalks or ophthalmites, which 
are modified limbs of one of the cephalic segments. (See 
cut under stalk-eyed.) A few crustaceans have a single 
median eye. In vertebrates, where the eyes are normal- 
ly never more nor fewer than one pair, these organs are 
received in special formations of the skull, the sockets or 
orbits of the eyes ; and the eyes are usually further defend- 
ed from accidental injury by various contrivances, as eye- 
lids, eyelashes, and eyebrows. (See these words.) Other ap- 
pendages of the eye namablo among its " defenses" are the 
lacrymal apparatus, which secretes tears to moisten the 
organ, and the glandular structures (Meibomian follicles), 
which serve for its lubrication by secreting a greasy sub- 
stance. The front of the eye has usually a special mucous 
membrane, the conjunctiva. The most essential or inti- 
mate parts of the organ of vision are contained in a globe 
or disk, the eyeball (which see), which is freely movable in 
its socket in the higher vertebrates, and rolled about by 
the action of various muscles, as the four recti and two 
obliqui of man and the choanoid muscle of some mam- 
mals. Externally the eyeball consists for the most part 
of a tough opaque membrane, the sclerotic; but in front, 
of a hard transparent structure, the cornea. These toge- 
ther are the outermost of three tunics or coats of the eye; 
the second tunic consists of the choroid coat and ciliarti 
processes and the iris, and the third and innermost of the 
retina, the expanded end of the optic nerve, which enters 
the ball from behind and spreads out upon the choroid to 
a varying extent. The retina receives optical impressions 
focused upon it by the crystalline lens, which are trans- 
mitted by the optic nerve to the brain, where they are 
sensed as visual images. The hollow eyeball with its sev- 
2103 
eral tunics forms a kind of camera filled with certain solid 
and fluid refractive media. Directly in the axis of vision in 
tin- interior of the ball is suspended a solid biconvex body, 
the crt/xld/lin' 1 tens, serving to bring rays of light to a focus 
on the retina. The lens, inclosed in its capsule, also di- 
vides the interior of the eye into two compartments. The 
larger rear compartment is tilled with a glassy fluid, the 
V 
Human Eye, in Median Vertical Anleroposterior Section. (Ciliary 
processes shown, though not all lying in this section.) 
A, anterior, and A', posterior chambers of aqueous humor ; a, cen- 
tral artery of retina ; C, cornea ; Ch, choroid ; </, conjunctiva ; cm, 
ciliary muscle ; cp. ciliary processes ; H, hyaloid ; /, iris ; L, crystal- 
line lens in its capsule f the reference-line passes through the pupil ) ; 
' 
/, /', insertion of tendon of superior and inferior rectus muscles ; t>, 
optic nerve ; P, canal of Petit ; R, retina ; 5, sclerotic ; s, s ', circular 
sinus or canal of Schlemm ; y, vitreous body filling back part of the 
eye. 
vitreous humor, inclosed in a delicate hyaloid membrane, 
which may also send prolongations through its substance. 
In front of the lens, between this structure and the cornea, 
the space is filled with a more watery fluid, the aqueous 
humor. This anterior space is partly divided into an an- 
terior and a posterior chamber by the iris, which hangs in 
front of the lens like a curtain with a hole in the middle, 
the pupil. Besides the optic nerve, or special nerve of 
sight, the eye is supplied with other motor, sensory, and 
sympathetic nerves, and has its appropriate blood-vessels. 
In man both eyes look directly forward, their axes being 
parallel, though the orbits in which they are contained 
present a little outward, or away from each other. The 
optic nerve follows the axis of the orbit, and consequent- 
ly pierces the eyeball behind, a little on the inner side 
that is, toward the nose. The muscles which move the 
ball are six, the rectus superior, rectus inferior, rectus ex- 
ternus, rectus interims, obliquus superior, and obliquus 
inferior. These muscles are innervated by three motor 
nerves, the oculomotor, trochlear or pathetic (distributed 
to the obliquus superior), and abducent (distributed to 
the rectus externus). The ball is embedded in a quantity 
of adipose tissue forming a soft cushion, but is also some- 
what isolated by means of a thin membranous sac called 
the vaginal tunic or sheath of the eye. The ball is near- 
ly spherical or globular, but is a little deeper and wider 
across than from before backward, measuring about an 
inch in each of the former axes 
and T% of an inch in the latter. 
(For the structure of the sev- 
eral tunics, see sclerotic, cor- 
nea, choroid, ciliary, iris, and 
retina.) The retina is an ex- 
pansion of the optic nerve into 
a large, circular, concavo-con- 
vex sheet, which rests upon 
the choroid with its inner sur- 
face in contact with the body 
of vitreous humor in the back 
of the eye. In the middle of 
it and in the axis of the eye is 
a little rounded elevation, the 
iica semilunaris; 6, pupil; 7", yellow spot, or macula lutea, 
with a depression at its sum- 
mit, the fovea centralis. To 
the nasal side of the yellow spot is the entrance of the op- 
tic nerve and of the central retinal artery ; and here the 
retina lacks the visual function which characterizes all 
the rest of its surface. The lens is suspended in a transpa- 
rent capsule in the axis of vision ; it is biconvex, and more 
convex on its posterior than on its anterior surface. It is 
about J of an inch across and } of an inch deep, and its 
structure presents concentric laminations. It tends to 
flatten with age. (See crystalline lens, under crystalline.) 
The vitreous humor fills the hollow of the eyeball behind 
the lens. It is a glassy or jelly-like substance, consisting 
chiefly of water, with a little saline and albuminous ma- 
terial, inclosed in a delicate hyaloid membrane continuous 
in front with the capsule and suspensory ligament of the 
lens, and behind resting upon the retina. Some prolonga- 
tions of the hyaloid enter the substance of this humor, 
and one of these is called the canal of Stilling . The quan- 
tity of vitreous humor, or hulk of the vitreous body, is 
about J of the entire mass of the eyeball. The aqueous 
humor is the slightly saline watery fluid which fills the 
eye in front of the lens, between this and the cornea, on 
both sides of the iris, consequently occupying the whole 
of the anterior and posterior chambers of the eye. Its 
bulk is very small. (See conjunctiva, lacrymal, Meibomian, 
nasal, ocular, ophthalmic, optic, palpebral, superciliary, 
tarsal, etc.) The eye agrees with other sense-organs in de- 
velopment in the embryo, in being partly formed by the 
inversion or involution of a portion of epiblast from with- 
out, anil partly by protrusion or evolution from within of 
a primitive ocular vesicle, the two coming together in the 
situation where the lens is to be developed. The result is 
that a portion of epiblast from the back of the embryo, 
which had been shut into the hollow of the cerebrospinal 
tube, pushes out from one of the cerebral vesicles to meet 
another portion of epiblast from the face of the embryo. 
Thus, the retina and associate parts are an outgrowth from 
Exterior of Left Human Eye. 
r, supercilium, or eyebrow ; 
2, palpebra superior, or upper 
eyelid ; 3, 3, cilia, or eyelashes ; 
4, caruncula lacrymalis; 5, 
I 
eye 
the undeveloped brain, while the lens and associate epi- 
thelial structures are an ingrowth of epidermis. In uther 
mammals with well-formed eyes the structure is substan- 
tially the same as in man, though minor and incidental 
variations are numerous. Theeyesof quadrupeds usually 
present laterally, and not directly forward. 'Jlit-y are usu- 
ally relatively larger and probably much more effective 
organs of vision than those of man. They frequently de- 
velop a special choanoid muscle or retractor of the eye- 
ball. The iris is commonly black, brown, or of some dark 
tint, seldom bluish or pale. It often contracts in such a 
way that the pupil is linear, elliptical, or narrowly oval, 
instead of circular, as in man. This is well seen in the 
cat. In birds several modifications occur. The eyeball 
is strengthened and its shape molded by a set of splint- 
bones or small bony plates disposed in a circle in the 
sclerotic around the cor- 
nea. The ball is hemi- 
spherical with an anteri- 
or projection, somewhat 
like a short acorn In a 
large cup, and the cornea 
is very convex. The pu- 
pil is always circular, 
though the iris may be 
so motile as to present 
only a narrow ring round 
the pupil, or to reduce 
the pupil to a mere 
point. These changes are 
well seen in the eyes of 
owls. There is also in 
the vitreous humor a pe- 
culiar plaiting or folding Right Eyeball of Bird, seen from 
of the choroid, called behind, showing the following mus- 
the marsupiuin or pec- cles : a, rectus superior ; *, rectus ex- 
ten. The visual range and ? ernus ; ' re s inferior; rf, rectus 
power of the eye in some qims inferior; f" quadratic; A.'rW 
birds, if not in all, are midalis, with its tendon, *, passing 
much greater than in through a pulley in the quadratus(as 
mn Allhlrrlshavprhrep shown by dotted line) to keep it off 
":,?,,, * V the optic nerve, ,', then passing around 
eyelids, the third very theec^eof the ball to its insertion in 
fully developed and ar- the nictitating membrane. 
ranged so as to sweep en- 
tirely across the front of the eye by means of special mus- 
cles and tendons upon the back of the eyeball. No birds 
are eyeless. In reptiles the eyes are structurally more like 
those of birds than of mammals. Some reptiles are eye- 
less, or have very rudimentary eyes. Most have eyelids, 
but these are wanting in ophidians, a transparent cuticle 
being continued directly over the ball, and shed with the 
rest of the cuticle. In fishes the eyes are generally sym- 
metrically lateral, but not infrequently dorsal and closely 
approximated to each other, and rarely inferior ; in one 
type, the heterosomes or flat-fishes, they are, however, 
both on one side, that belonging to the side which rests 
on the ground being in the very young in the normal po- 
sition, but soon actually penetrating through the integu- 
ment, and with the circumocular cranial region twisting 
to the opposite side and assuming a permanent position 
above the regular eye of the colored or uppermost side. 
The accessories of the eyes of mammals are undeveloped 
in fishes, but the eyes themselves are sometimes covered 
by a fold of the integument, and sometimes, as in some 
sharks, by a peculiar nictitant membrane. Among the 
most characteristic features are the flattening of the cor- 
nea and the sphericity of the crystalline lens. In one 
group (Anableps) a remarkable deviation from all other 
forms occurs, in that the cornea is divided by a horizontal 
band of the conjunctiva into upper and lower halves, and 
two pupils are developed, the species consequently being 
known as four-eyed fishes. In the lowest of the verte- 
brates (Branchiostoma) the eye is represented by a very 
small spot, coated with dark pigment and receiving the 
end of a short nerve. See vision. 
For he beholdethe every man so scharply, with dread- 
fulle Eyen, that ben evere more mevynge and sparklynge, 
as Fuyr. Mandemlle, Travels, p. 282. 
Our yeen ar made to looke ; whi shulde we spare? 
Political Poems, etc. (ed. Furnivall), p. 60. 
Thane the worthy kynge wrythes, and wepede with his 
enghne. Morte Arthure (E. E. T. S.), 1. 1920. 
There was he aware of a jolly beggkr, 
As ere he beheld with his eye. 
Robin Hood and the Beggar (Child's Ballads, V. 252). 
2. In a restricted or specific use, some part or 
appurtenance of the physical eye, taken as rep- 
resenting the whole, (a) The hole in the iris through 
which light enters ; the pupil : as, owls' eyes contract in 
daylight ; circular or oval eyes. (6) The socket of the eye ; 
the orbit : as, the empty eyes of a skull, (c) The opening 
between the eyelids ; the palpebral fissure : as, to close or 
shut the eyes. 
Figuratively 3. Vision; the act of seeing, or 
the field of sight; hence, observation; watch. 
Here will shee crosse the riuer ; stand in her eye, 
That she may take some notice of our neglected duties. 
Heywood, If you Know not Me, i. 
After this jealousy he kept a strict eye upon him. 
Sir R. L'Estrange. 
Then said Evangelist, Keep that light in your eye, and 
go up directly thereto, so shalt thou see the gate. 
Bunyan, Pilgrim's Progress, p. 86. 
The eye of the master will do more than both his hands. 
Franklin. 
4. The power of seeing; range or delicacy of 
vision; appreciative or discriminative visual 
perception : as, to have the eye of a sailor ; he 
has an eye for color, the picturesque, etc. 
I have a good eye, uncle ; I can see a church by daylight. 
Shak., Much Ado, H. 1. 
5. Mental view or perception ; power of men- 
tal perception ; opinion formed by observation 
or contemplation. 
