Abraham Metz.

The anatomy and histology of the human eye online

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from irritants. The upper punctum has a diameter of J"', and
is always located a little further inward than the lower, which
is a little larger than the upper.

The lachrymal canals (canaliculi lacrymales] have a length of
3'" to 4'", and in diameter they are J'" to "'. They begin at
the puncta, the upper running a short distance vertically up-
ward, and the lower a short distance vertically downward,
and with their outer walls are attached to the tarsi, so that
they are not only kept in a state of tension, but are always
kept open. Their posterior walls are attached to the conjunc-
tiva of the lids. From this point they are enveloped in the
connective tissue of the lids, and form an angle, bending con-
vergently inward to open into the lachrymal sac, beneath the
lower half of the inner lid-band (ligamentum canthi internum),
sometimes separately, and sometimes united into one canal.
They enter it always quite obliquely, so that their mouths are
closed by a fold of mucous membrane. The lower is V" shorter
than the upper, and larger in diameter.

Their inner surface is lined by a mucous membrane, which
is tender, pale, smooth, with few mucous glands, and is covered
by a lamellated pavement epithelium. These canals are freely
surrounded by the fibres of the lachrymal portion of the orbic-
ularis, in the manner described when treating of that muscle.
As rare exceptions, two puncta have been observed in one lid.

The lachrymal duct (ductus lacrymalis) lies behind the frontal
process of the superior maxillary bone, in the canalis lacry-
malis, and opens into the inferior ineatus of the nose. In con-
sequence of its course backward, it forms, with the floor of the
nasal cavity, an angle of 65, and to the vertical meridian an
angle of 5 to 10. It is about V" in length, and is divided
into 3 parts. (1) The lachrymal sac (saccus lacrymalis}', (2),
the part surrounded by a bony canal, the pars maxillaris
ductus lacrymalis ; and (3), into the lower, nasal portion, the
canalis naso-lacrymalis.

The lachrymal sac is 5'" to 6'" in height, and 2'" to 3"' in



OF THE HUMAN EYE. 179

breadth, of an elongated, oval, or almond form, being flattened
from before backward to such an extent that often, in the
cadaver, the two walls are closely pressed together (Stellwag).
One-half lies in the fossa lacrymalis. More than one-half of its
vertical expansion is below the rim of the inner, lower border
of the orbit. The upper half of the sac is, for some distance,
crossed by the lid-band. The upper cul-de-sac, or fundus,
passes 1J ; " above the upper border of the lig amentum canthi
internum. Behind this ligament the lachrymal canals perfo-
rate its outer wall. According to Arlt (Compte rendu du Con-
gres, 1863), only the upper third of the sac is covered by the
fibres of the lachrymal portion of the orbicularis (Homer's
muscle). The inner wall of the portion of the sac within the
lachrymal fossa, passes down vertically, and without any
change, into the inner wall of the membranous portion of the
lachrymal duct. Arlt says, that in many instances, the outer
wall of the sac, before opening into the bony portion of the
duct, forms a sinus or recessus. In cases where this sinus does
not exist, then there is also no mark of division on the outer
wall. In some instances there is a marked projection of the
mucous membrane at the point of division between the sac and
nasal duct, so that there is a marked constriction at this point.
In such instances there is greater development of the perios-
teum, or of the aponeurosis of the sac, at the point of entrance
into the bony canal.

The maxillary portion of the lachrymal duct is surrounded by
a bony canal, and is connected in its whole extent by the peri-
osteum. It is most constricted in the middle in a length of
3'" to 4'", and has a diameter of f '" to f '" Like the lachry-
mal sac, it always seems to be filled with fluid.

The nasal portion. The lachrymal duct does not terminate
with the bony canal at the inferior meatus of the nose, but
runs along 2"' to 3'" between the bony wall and the mucous
membrane of the nose, and with an oblique, narrow opening it
perforates the nasal mucous membrane at an acute angle. The
nasal portion then is only covered by a fold of the mucous



180 THE ANATOMY AND HISTOLOGY

membrane of the nose. Its nasal mouth is 7 /;/ to 9"' from
the anterior border of the frontal process of the superior max-
illary, and is 3 /r/ to 5'" above the floor of the nose. The
mou-th into the nose is longer from above down than trans-
versely, and varies from a slit y fr long to f '" wide, to an oval
opening of 2'" long to V" to \\"' wide. It is always filled
with fluids.

It often happens that at the opening into the nasal passage,
small duplicatures of the mucous membrane exist, which pro-
ceed either from above, from before and behind, or from behind,
but always lie flat on the Schneiderian membrane. These
cause the slit-formed mouth to be either horizontal, oblique,
vertical, or bent in the form of a bow.

The ductus lacrymalis has a thick mucous membrane, which
is rough, and is lined by a simple epithelium ciliare; in the lower
part, however, it possesses a lamellated pavement epithelium,
and has numerous racemose mucous glands.

In its whole extent, the duct is surrounded by a network of
firm connective tissue, which possesses elastic fibres. This
network is unusually rich in bloodvessels. These vessels,
which are connected with the surrounding bone, also richly
supplied with blood, fill up the interspaces, and in the cadaver
they do not collapse, so that they can be seen with the naked
eye. This stratum of vessels -is thin at the lachrymal sac, but
becomes much thicker along the nasal duct, especially pos-
teriorly, so that the duct is narrowed, and the mucous mem-
brane is projected inward and thrown into folds.

Outward the connective tissue becomes firm and tendinous,
which envelops the duct as a sheath in its whole extent. As
far as the bony canal extends this sheath is loosely connected
with it, and performs the function of periosteum.

On the outer wall of the lachrymal sac it forms a kind of
aponeurosis, which is attached to the edge of the lachrymal
fossa, which makes of it a closed canal or cavity. This apo-
neurosis is in intimate connection with the processes of the
posterior surface of the lid-band, as well as with the sheath of



OF THE HUMAN EYE. 181

the lachrymal portion of the orbicularis, through which it is
strengthened.

The bloodvessels and nerves of the lachrymal apparatus are
mostly branches supplying neighboring organs. The lachrymal
gland has a branch from the arteria ophthalmica, the arteria
lacrymalis; also a corresponding vein, which empties into the
vena ophthalmica. The nerves are derived from the nervus
infra-trochlearis, a branch of the first ramus of the nervus
trigemini, which, when irritated mechanically from without,
or from within emotionally, causes the rapid secretion of tears.



INDEX.



PAGE

Acinus glands of the conjunctiva, ... . . . . . 174

Apparatus, Visual, . . . ,. .. .. ... .. ... ,. ... 17

Aqueous humor, . . ,. . . . . . . .... .-h*-,.^* . 102

Arteries :

Ofchoroid, '..'., . . . ,. ,. .. . . .'vi, . . 33

Corpus ciliare and iris, . . . * . . . . .49

Of the eye, . . . . ... . . . . .125

Bloodvessels J

Cornea, . . .. ... . ,...,. . , ,-,. . 26

Ketina, . . . . . . . . . . ... . . t . . 79

Optic nerve, ....'..'... . 125

Eyelid, . /. *. . . . . . . < . . . . . .163

Bonnet's capsule, . . . . . . -..;. 19, 106

Bowman, Stratum of, . . .... . . . . .24

Cartilages, Tarsal, .. ,. . T. .... . . . .147

Choroid, -. i ,. .. . .. . . ,^ ; v f r ... 32

Texture, . . . . : . . ... * . . . . 36

Cloquet, Canal of, . . . .....,.,. . ^ , -;* . . 96

Conjunctiva, . . . . .,.,.... . . 165

Cornea, . . ". .... .. .. .. . .. .. -y^ 18,32

Minute structure, . . , . , . ... , * . . . . . . 22

Bloodvessels, ........... 26

Nerves, .......... 27

Corpus ciliare, . . . . . . . . .40

Crystalline lens, . f . .... ... . . . 82

Descemet, Membrane of, . . i . . . . .25

Divisions of choroid, . '" . .. ".'...'. . . . 32

Eye, Description, . . . ^ . ' . . ,.. . . . 17

Eyeball, Description, . . . v , . . .17



INDEX. 183

PAOK

Eyelids, 145

Eyelid :

Bloodvessels, . . . . . . . . . . .163

Nerves, . . . . -. . . . . . . . . . 165

Eyelashes, . ... . , . . . . .. . . . 162

Ganglion cells, . ... . . . . . . . . 66

Granular layer of retina, . . . . . . . . .62

Homer's muscle, . .. . . . . . . . . . 155

Iris, . /.-. -. . -. ' . l j"4*fV',^ ( W 45

Bloodvessels, ........... 49

Jacob's membrane, ........ ; .; *''. 57

Lachrymal :

Canals, ... .... . . . . . .178

Duct, (*B& . 178

Gland, ...... . . . . <. . - -.-:>;- ''... 175

Lens, Crystalline, . . . . . .' ' ^?/. 82

Capsule, .=...,. . . . . -* . -. . 83

Lymphatic glands, V . 172

Vessels, . . . ". . ..,'.' . .'. -v . ;.. . 171

Macula lutea, . . . .77

Meibomian glands, .-*.. . . . . . J< v I . . 149

Membrana chorio-capillaris, . 35

Membrana limitans retina?, ......... 69

Morgagni, Liquor of, . '.,.,. . . . . ,^. . . 89

Muller, Fibres of, . . .;.,,* . . ,. . .. '.M. '- ,,-* 62

Muscle, Ciliary, . . ; . . : . . . ,.,.,. . ,.* 40

Of iris, . . <. ..... . ,. f .-.^-.-. '.-'-.ir .,-^-f* . 46

Muscles of eye, . . . . .. .. ,. -.** .-?.:-*.,>-. . 108

Action of, . . ,. .... -. . '-. . .. -^. 111,116

Nerves :

Cornea, . . . . . . . . . . .27

Iris and ciliary muscle, ......... 53

Optic, 118

Of eye, 134

Eyelid, . .165

Nervous tissue of retina, .......... 57



184 INDEX.

PAGE

Optic nerve, 118

Axis, 112

Fibres, lamina of, . . . . . . . . .68

Orbicularis palpebrarum, . . . . . . . . . 151

Orbit, 104

Papilla nervi optici, . . . . . . . . .79

Retina, . . . . ''.-. . . . . .65

Area, . . ; . . . ' . . . . ' . . . 76

Cellular tissue, . . . . . V . . . .70

Relations, . . . . ... - ... . . 76

Thickness, ... . .' . ... . 76

Rods and cones (Jacob's membrane), . . . .',..'. 57

Sclerotica, . . . , . . . . . . , .. 18,32

Scblemm, Canal of, . . . . . . . . .42

Tarsal cartilages, . . .... . . . . 147

Tears, Analysis of, . . . , . . . . . . . 177

Tenon's membrane, . . ..... . . . ' . . . 19

Capsule, .-...". . . . . . . . .106

Tunic, Fibrous, . ... . . .. .. . . . . 18

Uvea, . . . . . . . .47

Vascular tunic (choroid), . . . . ' . . . .32

Veins:

Choroid, . . . . . . f ' ; ' . . . .35

Corpus ciliare and iris, . . . . ... . .50

Of eye, . . -. ..... . . .128

Venae vorticosae, . . . . . . . . . . 35

Vitreum corpus, . . . . . . . . . .94

Zinnius, Zone of, . . . . ... . . .43,82,98





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Online LibraryAbraham MetzThe anatomy and histology of the human eye → online text (page 14 of 14)