the retina to fall apart.
348 MANUAL OF HISTOLOGY.
The optic nerve, after leaving the optic canal, passes through
the orbit surrounded by three coverings, continuations of the
The dural coat, composed of dense connective tissue with a
few elastic fibres, forms the outer covering ; the fibres are at-
tached to the periosteum, where the nerve leaves the bony canal,
and where it enters the eyeball they are continued directly into
the outer layers of the sclera.
Within this covering, and separated from it by a very nar-
row space, are the delicate fibres of the arachnoidal coat,
and the lymph-space between the two is called the subdural
Within the arachnoidal coat, and separated from it by a
wide lymph-space, is the pial coat closely surrounding the
nerve-fibres, and sending processes of connective-tissue be-
tween their bundles. This membrane passes into the inner
layers of the sclera, and also sends numerous fibres to the la-
mina cribrosa. Its outer surface is covered with endothelium,
and between it and the arachnoid coat is the subaraclinold
space, which reaches to the inner layers of the sclera, and is
continuous with the same space in the brain.
The optic nerve itself, closely surrounded by its vagina
fibrosa, passes forward through the orbit, receiving the central
artery and vein at about 15 to 20 mm. from the sclera. These
vessels pass to the centre of the nerve and lie in a connective-
tissue sheath until they emerge on the inner surface of the eye-
ball to branch over the retina.
On cross-sections of the nerve, bundles of connective tissue
are seen to pass inward from the pial sheath and form a cross-
network, through the openings of which the nerve-fibres pass.
On longitudinal sections the connective tissue appears in
irregular fenestrated sheaths ; this tissue can also be demon-
strated by macerating thick sections in a J per cent, solution
of chromic acid and then brushing out the nerve-elements.
These nerve-filaments themselves are extremely small, but
vary somewhat in size. They consist of an axis-cylinder sur-
rounded by its medullary sheath; they are grouped in large
bundles which pass through the meshes of the connective tis-
sue. The fibres appear to be held fogether by a kind of homo-
geneous albuminous substance neuroglia, and have on their
surface occasional nucleated corpuscles, distinguished from
THE EYE. 349
those of the connective tissue by being larger and more irregu-
lar in shape.
Blood-vessels are found not only in the centre of the nerve,
but also scattered through various parts of the connective tis-
At the lamina cribrosa there is an anastomosis with the ves-
sels of the circle of Holler, which, coming from the short poste-
rior ciliary arteries, forms a vascular circle in the sclera, about
the entrance of the optic nerve.
Where the nerve-fibres pass through the sieve-like openings
of the lamina cribrosa they lose their medullary sheath, and
from that point pass on to the nerve-fibre layer of the retina
as transparent axis- cylinders ; but in rare cases the sheaths are
continued from the optic disk some little distance over the
retina, and are seen with the ophthalmoscope as very white
patches radiating out from the disk, or following the vessels
and gradually fading into the general color of the f undus by
a fine, fringe-like border.
The vitreous body is a transparent, jelly-like mass, of spher-
ical shape, with a depression at the anterior part, in which the
lens rests. It is bounded behind and on the side by the retina,
in front by the lens with its attachments, and appears to have
no true hyaloid limiting-membrane of its own. It is very diffi-
cult to demonstrate any definite structure in this substance ;
toward the periphery it appears to be arranged somewhat in
concentric layers, but in the centre is more homogeneous.
From the optic disk to the lens there is a small canal about
1 mm. wide in front and spreading out behind ; it is lined
with very transparent cells, and filled with a substance more
fluid than the rest of the vitreous ; it marks the position of the
arteria hyaloidea^ which is usually obliterated at about the
seventh foetal month.
The vitreous body also contains numerous corpuscles, espe-
cially near the periphery ; these consist of round lymph- cells,
stellate cells, with one or more nuclei, and irregular arms, and
of branching cells which seem to have a transparent vesicle
filling up a part of their interior. The vitreous contains no
nerves, and after birth no blood-vessels ; it may be examined
fresh or hardened in a \ per cent, solution of chromic acid.
Sections may be colored blue with aniline, and preserved in
MANUAL OF HISTOLOGY.
The lens (Fig. 158) is a transparent, biconvex body, sur-
rounded by a structureless, elastic capsule, which is thicker in
front where it touches the iris, and thinner behind where it
rests in the fossa patellaris of the vitreous.
The inner surface of the anterior capsule is covered with a
single layer of hexagonal epithelial cells, which become longer
near the equator of the lens, and gradually pass over into the
After birth these fibres consist of long, transparent tubes, on
section resembling flattened hexagons closely joined together
by their serrated edges; they are
arranged in concentric meridional
layers with their broad side out-
ward. They do not pass around
the entire circumference of the lens,
but arise on the anterior surface
from three lines, which, uniting at
the axis, make a figure like an in-
verted Y, with the arms set at an
angle of about 20 to each other ;
on the posterior surface this star
is reversed, the Y standing upright.
In adult life the rays are more
numerous, and the fluid contents
of the tubes become more solid and
of greater refractive power, espe-
cially toward the centre of the lens.
On a meridional section of the
lens one sees the concentric ar-
rangement of the lens-fibres, and near the equator a collection
of nuclei (the nuclear zone). These nuclei belong to the lens-
fibres, each one of which originally had one, although in
adult life they are found more abundantly in the peripheral
The fibres of the supporting ligament of the lens (the zonula
ciliaris) are attached to the anterior and posterior capsule near
the equator ; from here they converge to the apex of the ciliary
body, to which they are fastened.
The fibres form for the most part an anterior and posterior
layer, and have occasional nuclei, especially toward the ora
serrata ; between these layers is the canal of Petit, the result
Fio. 158. Meridional section through
axis of the human lens.
THE EYE. 351
of post-mortem changes, which quickly destroy the delicate
fibres that ordinarily lill this space.
Specimens for study may be made in the following way :
harden an eye for fourteen days in Muller's fluid ; then open,
remove the lens, and preserve in alcohol. Sections may be
made in any direction ; they should be colored with hema-
toxylon and mounted in glycerine.
To examine the epithelium under the anterior capsule, a
piece of capsule should be peeled oif from a fresh lens and ex-
amined with or without previous staining. Single lens-fibres
or groups of fibres may be obtained by macerating a portion
of lens in dilute sulphuric acid ( per cent.), or in a -J per
cent, solution of chromic acid, after which it can be easily
separated into its elementary parts.
The lachrymal gland is situated under the upper and outer
edge of the orbital wall, resting partly in a shallow fossa of the
frontal bone, to which it is attached by r firm bands of connec-
It is an acinous gland, divided into a larger upper portion
(glandula Galeni), some 20 mm. long, 10 wide, and 5 thick, and
a lower part of about half the size (glandula Monroi) ; they are
supplied with blood by a branch of the ophthalmic artery, and
with nerves from the fifth pair.
The connective tissue which envelops the gland also ramifies
through its substance, dividing it into numerous small alveoli,
in which are the true secreting cells of the gland, and from
which fine ducts pass out to coalesce, and finally discharge on
the free surface of the conjunctiva fornicis at its upper and
The upper part of the gland is quite dense, but in the lower
portion the alveoli are less closely packed, and often near-
ly surrounded by the orbital fat. The alveoli are covered
by a fine membrane composed of flat cells with numerous
branches or processes, which spread in various directions and
serve to unite the cells of the investing membrane, and also the
different alveoli ; they form a shell which is surrounded on its
outer side by a distinct lymph-space, and on its inner surface
is Jined by the secreting cells of the gland.
If these lymph-spaces have been injected with Berlin blue,
and especially if the blood-vessels are injected with some other
color, the arrangement of the lymph-spaces can be very well
352 MANUAL OF HISTOLOGY.
seen. The openings from the alveoli are at first lined with
fine, fiat cells ; then, as the tube grows larger, they assume the
character of cylindrical epithelium.
GRAEFE u. SAEMISCH. Handbuch der gesammten Augenheilktmde. Vol. I,
J. ORTH. Cursus der normalen Histologie. Berlin, 1878.
A. ALT. Lectures on the Human Eye. New York, 1880.
BY DRS. WILLIAM F. WHITNEY AND CLARENCE J. BLAKE, OF BOSTON.
FOLLOWING the natural order are to be considered, first, the
external ear with the meatus externus ; secondly, the middle
ear with the Eustachian tube; and thirdly, the internal ear
(membranous labyrinth and cochlea).
External ear. This includes the auricle, the meatus exter-
nus, and the membrana tympani.
The auricle is formed by a cartilaginous plate, 1-2 mm. in
thickness. The fine elastic fibres of this plate, which is of the
reticular variety of cartilage, can be traced into the perichon-
drium, and even into the subcutaneous tissue. Both perichon-
drium and subcutaneous tissue are rich in elastic fibres, the
latter varying greatly in amount in different parts of the ear,
being very sparingly developed on the concave surfaces, where
the skin is closely adherent to the perichondrium, and immov-
able in consequence, but more abundant on the convex sur-
faces, where the skin is movable ; it forms, together with the
fat enclosed in its meshes, the bulk of the lobule.
The cutis covering the auricle is a direct continuation of
that covering the face, and is well provided with downy hairs
and sebaceous glands. These latter reach their greatest devel-
opment in the depressions of the auricle, especially the concha.
The external meatus consists of a cartilaginous and an os-
seous portion. The former only differs in structure from the
auricle into which it passes, in the presence of the ceruminous
glands. These are tubular glands, having a coil at the bottom.
They consist of a membrana propria, on which is a layer of
cubical epithelium, and are the analogues of the sweat-glands.
In the osseous portion of the meatus the glands are sparingly
found, and the hairs are fewer and finer. Otherwise there is
354 MANUAL OF HISTOLOGY.
no difference between the two portions, except that the carti-
lage is replaced by bone.
The ear of a new-born child can be easily removed with the
cartilaginous part of the meatus, and when hardened in Miil-
ler's fluid and afterward in alcohol, and imbedded in parafnne
or hardened liver, furnishes sections which, when colored with
hsematoxylon, show the different relations very clearly. The
osseous portion must first be decalcified by allowing the bone
to hang freely in a weak (-J- per cent.) solution of chromic
acid, often renewed, during several months. The specimens
are then to be well washed, hardened in alcohol, and prepared
At the inner end of the external meatus, and separating it
from the middle ear, is stretched the membrana tympani. The
tympanic ring, with the membrane attached to it, is to be care-
fully separated from the surrounding parts by means of bone-
scissors, and placed for five to fifteen minutes in a weak solu-
tion (two to five per cent.) of formic or acetic acid. It shoiild
then be well washed in distilled water, and the external layer
of epithelium removed by a camel' s-hair brush, arid finally
stained with hsemotoxylon and mounted in glycerine. In spe-
cimens thus prepared there are to be distinguished three lay-
ers, viz.: an external or cuticular layer, a middle or fibrous
layer (membrana propria), and an internal or mucous layer.
The cuticular layer is composed of simple pavement-epithe-
lium, without glands or hairs. It is thickest at the periphery,
and over the handle of the hammer, and along its edge.
The fibrous layer (membrana propria) consists of two sets
of flattened, spindle-shaped fibres, with long, thin connective-
tissue corpuscles imbedded in them, and which have a close
analogy with the fibres of tendons. The outer series, lying
directly beneath the cutis, radiates from the handle of the
hammer toward the periphery, while the inner series circles
about the handle. At the periphery the two series interlace
with each other and with a few fibres coming from the cuticu-
lar and mucous layers to form the so-called tendinous ring, in
which are also to be found a few scattered cartilage-cells. This
ring is joined to the annulus tympanicus by a thin periosteum.
(The handle of the hammer is joined to the membrana tympani
by a cartilaginous formation which stands in close relation to
the membrana propria. This is a shallow groove of hyaline
THE EAR. 355
cartilage, in which the handle of the hammer lies, kept in place
by the mucous layer which passes over and is firmly adherent
to it ; the upper part of this furrow ends in a sort of cartilagi-
nous cap, into which the processus brevis fits.) Transverse
sections made after hardening the membrane in Muller' s fluid
and alcohol, and then imbedding, give the best idea of these
The inner or mucous layer is formed of flat epithelium, sup-
ported on a reticulated layer of connective tissue, and directly
continuous with the epithelial lining of the middle ear. The
arterial supply is furnished by a small arteriole, which follows
the handle of the malleolus, and gives off lateral capillaries
anastomosing with others coming from small branches which
enter at the periphery. The blood is collected into venous
trunks which pass out in a similar manner. Fine nerves are
said to be found in close connection with the vessels. They
apparently come from the sympathetic system.
The middle ear. In order to obtain a clear idea of the rela-
tions and structure of the middle ear a fresh temporal bone,
with the soft parts still adherent, must be decalcified by soak-
ing for a long time in a i per cent, solution of chromic acid,
which should be frequently changed; it is then to be washed
in distilled water for twenty-four hours, and hardened in alco-
hol, when it will be ready for cutting.
A section from a specimen thus prepared shows that the
whole middle ear is lined by a layer of pavement-epithelium,
supported upon two layers of connective tissue, one serving as
a submucous layer and the other as a periosteum. This tis-
sue is thrown into ridges corresponding to the bony promi-
nences, in the hollows of which the vessels and nerves lie. Ac-
cording to Kessel the submucous layer is provided with oval
expansions, recalling the Pacinian bodies found in the mesen-
tery of the cat. The existence of muciparous glands in the
human tympanum has yet to be confirmed. A plex"us of nerves
is described as distributed in the subepithelial tissue, in the
nodal points of which are found scattered ganglion-cells. The
lining of the tympanum passes directly into that of the mastoid
cells, and has there the same general arrangement.
Tlie Eustachian tube. In direct communication with the
tympanum stands the Eustachian tube, composed like the ex-
ternal ear of a cartilaginous and an osseous portion. The car-
MANUAL OF HISTOLOGY.
til age, which gives the name to the anterior part of the tube
that stands in connection with the pharynx, is in the form of
a hook (Fig. 159, 2), with its short end directed downward and
inward. At the bend of the hook the opposing surfaces of car-
tilage cannot quite apply themselves to each other, and there
is thus left a little air-space between them, which Ruedinger
has termed the safety- tube (Fig. 159, 9). The cartilage is of the
hyaline variety, with small cells, which are much smaller and
more numerous at the periphery, thus forming a sort of peri-
Fio. 159. Transverse section of Eustachian tube and surrounding parts : 1, median cartilaginous plate ;
2, lateral cartilaginous hook : 3, muscnlus dilator tubae ; 4, musculus levator veli palatini ; 5. fibro-carti-
lago basilaris : 6 and 7, acinous glands ; 8, deposit of fat in the lateral wall : 9, safety-tube ; 10, accessory
fissure ; 11, fold of the mucous membrane ; 12, adjacent tissues. Ruedinger.
chondrium. The cartilage is joined to the osseous portion by
a narrow band of fibro-cartilage.
The musculus dilator tubse (Fig. 159, 3), which goes to form
the membranous (muscular) portion of the tube, is joined to
the short end of the hook along the whole length of the carti-
laginous portion. The muscle is of the striped variety, and is
inserted into the perichondrium by means of a very short, flat
The entire tube is lined with a mucous membrane (Fig. 159,
11), continuous at one end with that of the pharynx, and at the
THE EAR. 357
other with, that of the tympanum. This membrane consists of
several layers of cylindrical epithelial cells, the upper or inner
of which have their broad surfaces directed inward and carry
cilia. In the other layers the epithelia are wedge-shaped. The
epithelium rests upon a basement-membrane, beneath which is
a layer of connective tissue (Fig. 159, 5), in which lie the muci-
parous glands (Fig. 159, 6, 7), which are similar to those of
the pharynx and oesophagus, and lined with wedge-shaped
epithelium. These glands are absent in the safety-tube. A
plexus of nerves arising from the pharyngeal and tympanic
plexuses has been demonstrated, the final distribution of which
to the glands is probable.
Before leaving the middle ear a short mention of the os
sicula and their mode of articulation is in place. The bones
are composed of an internal spongy and an external compact
portion. The former is very rich in blood-vessels. These
bones are covered in early life by the mucous membrane only,
but in later life there is also a thin periosteum to be seen.
Their articulation with each other is constructed similarly to
that of the larger joints; i.e., their articular ends are sur-
rounded by a capsule in which is a synovial fluid. The method
of union of the foot- plate of the stapes with the fenestra ovale
is a little more complicated. The bottom and edges of the plate
are covered with a thin film of hyaline cartilage. The edges of
the window are also covered with cartilage, which is united to
that of the plate by means of a fine network of elastic tissue.
The base of the plate rests upon a firm connective-tissue layer,
a continuation of the periosteum lining the inside of the scala
tympani, and called the ligamentum baseos-stapedis.
The muscles connected with the ossicula belong to the
striped variety, and are connected to the bones by tendons,
which are covered by the mucous membrane wherever they
pass through the tympanum.
The internal ear. The internal ear consists of two portions,
to which the auditory nerve is finally distributed, and which
are the essential parts concerned in the perception of sound.
These are the membranous labyrinth and the cochlea.
In man and the higher vertebrates both of these parts are
enclosed within bony walls, a circumstance which makes their
histological study a matter of considerable difficulty. In fishes,
however, although the cochlea is represented merely by a small
358 MANUAL OF HISTOLOGY.
diverticulum (the lagena), the membranous labyrinth is fully
developed, and, as it is large and easy of access, has always
been a favorite object for demonstration. Its method of prep-
aration will be given here, while that for the cochlea will be
described farther on.
The membranous labyrinth. Our knowledge of this part
has been chiefly derived from studies upon the pike (esox lu-
cius), perch (perca fluviatilis), or cod (gadus morrhua). The
head is divided longitudinally in the median line, and the brain
carefully removed by means of the handle of a scalpel, when
there is seen directly behind the eye a second cavity filled with
a grayish translucent mass, composed principally of fat and a
sort of mucous tissue. This can be removed with the aid of
fine forceps, and there is usually drawn out at the same time
more or less of the semicircular canals with their ampullse and
the remains of the utricle and saccule. With a little practice,
and by carefully freeing the canals from the short, bony chan-
nels by which they are held in place, the membranous laby-
rinth, with a portion of the acoustic nerve, can be removed
Within the utricle and saccule are found the otoliths, con-
cretions of lime. After the lime has been removed by means
of a weak acid, they show a coarse, fibrillated structure on
section. These serve as a ready means of distinguishing be-
tween the saccule and utricle, as the largest otolith (called
sagitta) and the smallest (asterix) occupy the saccule, the
former lying on the expansion of the acoustic nerve in the sac-
cule proper, while the latter lies on the expansion of the nerve
in that part of the saccule called the lagena, and which corre-
sponds to the cochlea of the higher animals. The medium-sized
stone (lapillus) lies upon the expansion of the nerve in the utri-
cle. The otoliths are embedded in a mucilaginous mass lying
directly upon the termination of the nerve. In the higher ani-
mals they are represented by cretaceous particles in the macula
The labyrinth thus removed is to be placed, during twenty-
four hours, in a 1 per cent, solution of osmic acid, and then
carefully washed in distilled water. In order to obtain the
separate cells, the point where the nerve enters (known by its
darker color) is to be carefully teased with fine needles and
examined in glycerine. To obtain good sections, the por-
THE EAR. 359
tions of the canal where the nerve terminates, and the simi-
lar portion of the saccule and utricle, are to be placed for
twenty-four hours in a saturated solution of gum arabic in
water, and then directly into strong alcohol for twenty-four
hours longer, when they will be ready for embedding. The
sections, made with a sharp razor, kept well wet with alcohol,
are to be deprived of their gum by passing a stream of distilled
water beneath the cover-glass, the water being replaced by a
solution composed of one part of a saturated solution of ace-
tate of potash and four parts each of glycerine and water.
The structure and arrangement of the semicircular canals,
except at the points of expansion of the nerve, is as follows :
In the osseous fishes the canals lie embedded in a mass of adi-
pose tissue, and are held in place by very short bony tubes ;
in the cartilaginous fishes (shark, skate) they lie in canals hol-
lowed out in the cartilage, while in man and the higher verte-
brates they are surrounded by bony walls.
In man the membranous part does not entirely fill up the
bony canals, but is adherent to the lining periosteum at one
point, and to the rest of the wall by bands of connective tissue
(called ligamentum labyrinth! canaliculorum et sacculorum), in
the interstices of which the perilymph circulates. In the fishes
the walls of the tubes and ampullae, as well as of the utricle
and saccule, are composed of what has been termed spindle-
cartilage. This consists of a homogeneous ground-substance,
like that of ordinary cartilage, in which lie embedded long,
spindle-shaped connective-tissue corpuscles, anastomosing with
each other in all directions, like the corpuscles of the cornea.
The whole is lined with a pavement-epithelium. In man the
structure is different. Here there are to be distinguished three
layers, viz., externally, a layer of connective tissue, composed
of fibrous tissue with numerous nuclei. This is connected at
one point with the periosteum, and passes into the ligamenta