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fibrillar. These fibrillar processes give rise to the chain which connects the  
 
fibrillar. These fibrillar processes give rise to the chain which connects the  
 
ganglia, and also to the grey rami communicantes and the various visceral  
 
ganglia, and also to the grey rami communicantes and the various visceral  
branches.  
+
branches.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
CHAPTER XVI
 
 
 
 
 
THE EYE
 
 
 
 
 
The eyeball is almost spherical. It consists of the segments of two
 
spheres—namely, a large posterior or sclerotic segment, which is
 
opaque, and a small anterior or corneal segment, which is transparent.
 
The sclerotic segment forms five-sixths of the eyeball, and the corneal
 
segment one-sixth. The centre of the corneal segment is called the
 
anterior pole, and the centre of the sclerotic segment is known as
 
the posterior pole. The sagittal (antero-posterior) axis, or axis of
 
vision, of the eyeball is represented by a line connecting the anterior
 
and posterior poles. The equator is represented by a line encircling
 
the centre of the eyeball in a coronal plane, the diameter of the circle
 
being about I inch. The plane of this circle would therefore divide
 
the eyeball into two halves—an anterior half, consisting of the corneal
 
and the front part of the sclerotic segment, and a posterior half, consisting of the back part of the sclerotic segment. The meridian is
 
represented by a line encircling the eyeball horizontally at right
 
angles to the equator, and passing through the anterior and posterior
 
poles.
 
 
 
Posteriorly the eyeball receives the optic nerve, which pierces
 
the sclerotic coat at a point about J inch to the inner side of and
 
about -f T inch below the posterior pole.
 
 
 
The eyeball is composed of three coats concentrically arranged:
 
(i) an external coat, consisting of an opaque part, called the sclera,
 
and a transparent part, called the cornea; (2) a middle coat, which is
 
vascular, pigmented, and muscular, and consists of (a) a posterior
 
part, called the choroid coat, (b) an anterior part, the iris, and (c) an
 
intermediate part, representing the ciliary body; and (3) an internal
 
 
 
coat , called the retina. .
 
 
 
These three coats enclose the following refracting media : (1) a fluid,
 
called the aqueous humour, which lies between the cornea and the
 
crystalline lens, where it occupies the anterior and posterior chambers,
 
into which this region is divided by the iris; (2) a solid body, called
 
the crystalline lens, which lies behind the aqueous humour, and (3) a
 
soft gelatinous body, called the vitreous body, which occupies the laige
 
space behind the crystalline lens.
 
 
 
 
 
Coats of the Eyeball.
 
 
 
External=sclera and cornea.
 
 
 
Middle =choroid, ciliary body, and iris.
 
Internal = retina.
 
 
 
 
 
Refracting Media.
 
 
 
Aqueous humour.
 
Crystalline lens.
 
Vitreous body.
 
 
 
 
 
T64T
 
 
 
 
 
1642
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
External Coat.
 
 
 
Sclera (or Sclerotic Coat).—The sclera (white of the eye) is a strong
 
white fibrous coat of great density, which surrounds the posterior
 
five-sixths of the eyeball, and maintains the shape of the organ. Anteriorly it unites, and becomes continuous with the cornea, which it
 
slightly overlaps. The junction of the two is indicated by a slight
 
groove, called the sulcus sclerce, and the union is known as the corneoscleral junction . Posteriorly, as has been shown above, the sclera is
 
pierced by the optic nerve a little below and to' the inner side of the
 
centre. The part of the sclera corresponding to the optic entrance
 
 
 
Levatoi Palpebras Superioris
 
 
 
 
 
Fornix Conjunctive
 
 
 
Fig. 1005.—Vertical Sagittal Section of the Eye and its
 
Appendages (Hirschfeld and Leveille).
 
 
 
is pierced by a number of openings for the passage of the fasciculi
 
of the optic nerve, and hence is called the lamina cribrosa.
 
 
 
Around the optic entrance there are numerous minute openings
 
for the ciliary vessels and nerves, and here the dura matral sheath of
 
the optic nerve blends with the sclerotic coat. About midway between
 
the optic entrance and the corneo-scleral junction the sclera is pierced
 
by four openings for the passage of the vence vorticosce of the choroid.
 
 
 
The sclera is thickest posteriorly around the optic entrance. It
 
is also thick near the sclero-corneal junction, where it receives the
 
insertions of the recti muscles.
 
 
 
The outer surface of the sclera is covered by a membranous investment, called the fascial sheath of the eyeball (fascia bulbi or capsule
 
of Tenon), and between the two there is the episcleral lymph-space (or
 
 
 
 
 
Hyaloid Canal
 
(Canal of Cloquet)
 
 
 
 
 
Hyaloid Membrane
 
 
 
 
 
Retina
 
 
 
>
 
 
 
 
 
Sinus Venosus Sclera?
 
 
 
 
 
Anterior
 
Chamber \
 
 
 
 
 
. Choroid
 
 
 
 
 
Rectus Superior
 
i „--Sclera
 
 
 
 
 
Arteria
 
z Centralis
 
 
 
 
 
 
 
/ Retinas
 
 
 
 
 
Cornea
 
 
 
Ciliary / y.
 
Processes'’ ft
 
 
 
Zonuiar Space
 
 
 
 
 
Rectus Inferior
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1643
 
 
 
 
 
Tenon’s space), which is broken up into a reticulum by processes of
 
connective tissue which pass between the sheath and the sclera.
 
This space communicates with the subdural and subarachnoid spaces.
 
The inner surface of the sclerotic coat is dark brown, and has grooves
 
for the ciliary vessels and nerves. It is lined with connective tissue
 
containing pigment-cells, forming the lamina fusca. Processes from
 
this layer pass to the choroid coat, and these, together with vessels
 
and nerves, traverse an interval, which represents the perichoroidal
 
lymph-space. This space communicates with the episcleral lymphspace through the vascular openings in the sclera. Anteriorly the sclera
 
blends with the cornea at the sclero-corneal junction, the sclera slightly
 
overlapping the cornea. Posteriorly around the optic entrance the
 
sclera blends with the dura matral sheath of the optic nerve.
 
 
 
Structure.—The sclera is composed of fibrous tissue mixed with
 
elastic fibres, and contains many connective-tissue corpuscles. The
 
fibres are arranged in bundles, which are disposed longitudinally and
 
transversely, and interlace with one another. The connective-tissue
 
corpuscles occupy spaces between the fibres, which may be regarded
 
as lymph-spaces.
 
 
 
Arteries.—These are the short ciliary group of posterior ciliary
 
arteries, and the anterior ciliary arteries, which are branches of the
 
ophthalmic. The vessels belonging to the former group are disposed
 
in the form of capillary networks; whilst the vessels derived from the
 
latter form a ring near the sclero-corneal junction beneath the conjunctiva, to which ring they converge in the substance of the
 
sclerotic coat.
 
 
 
The sclerotic veins open into the anterior ciliary veins, and into
 
the vencB vorticosce of the choroid. There is also a slight drainage
 
into the sinus venosus sclerce , a minute channel running deeply at the
 
sclero-corneal junction.
 
 
 
Nerve-supply.—The ciliary nerves.
 
 
 
Cornea.—The cornea is the transparent part of the external coat
 
of the eyeball, of which it forms the anterior sixth, and serves to
 
transmit light. It is almost circular, its transverse measurement being
 
slightly greater than the vertical. At its circumference it is continuous with the sclera, by which it is slightly overlapped. The anterior
 
surface is convex. The posterior surface is concave, and forms the
 
anterior boundary of the anterior chamber of the eye.
 
 
 
Structure.— The cornea consists of the following five layers, from
 
 
 
before backwards: .
 
 
 
1. The conjunctival epithelium.
 
 
 
2. The anterior elastic lamina.
 
 
 
3. The substantia propria.
 
 
 
4. The posterior elastic lamina.
 
 
 
5. A layer of endothelium.
 
 
 
The conjunctival epithelium is stratified, there being not less than
 
five strata of cells, and is continuous with the epithelium, which covers
 
 
 
 
 
1644
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
^ \ Stratified Epithelium of
 
/ Conjunctiva
 
Membrane of Bowman
 
or Anterior Elastic
 
Lamina
 
 
 
 
 
the free surface of the conjunctiva. The cells of the deepest stratum
 
are columnar; succeeding these there are layers of polygonal cells;
 
and these in turn are overlaid by layers of squamous cells.
 
 
 
The anterior elastic lamina (Bowman) is probably of the same
 
nature as the fibrous portion of the substantia propria. It is closely
 
connected with the substantia propria, is thin, and contains no
 
corpuscles.
 
 
 
The substantia propria is composed of modified connective tissue
 
arranged in bundles which form superimposed laminae. These laminae
 
amount in number to about sixty. The fibres of alternate laminae
 
cross each other at right angles, and at the circumference of the cornea
 
 
 
they are continuous with
 
 
 
 
 
the fibres of the sclerotic.
 
The successive laminae are
 
connected by cement substance, and within this
 
substance are branched
 
spaces, called the corneal
 
spaces or lacunae, which
 
communicate with each
 
other by very delicate
 
canaliculi. Each of these
 
spaces contains a nucleated connective-tissue corpuscle, called the corneal
 
corpuscle. These corpuscles, like the spaces which
 
they occupy, are branched,
 
and the offsets of adjacent
 
corpuscles communicate
 
with one another. As seen
 
in vertical sections of the
 
cornea, the corpuscles are
 
spindle - shaped, but in
 
 
 
 
 
 
 
Substantia Propria
 
 
 
 
 
Posterior Elastic
 
Lamina or
 
 
 
Membrane of Descemet
 
'Single Layer of Squamous
 
Epithelium lining
 
Descemet’s Membrane
 
 
 
 
 
Fig. 1006.—Vertical Section of the Cornea
 
 
 
(magnified) .
 
 
 
 
 
horizontal sections they appear flattened out, and give off their
 
branches.
 
 
 
The posterior elastic lamina (or membrane of Descemet) covers
 
the posterior surface of the substantia propria. It is thicker than the
 
anterior elastic lamina, and .is composed of an elastic homogeneous
 
membrane, which is very brittle. When stripped from the substantia
 
propria it comes away in shreds, and these curl up at their ends in
 
such a manner that the anterior or attached surface of each shred is
 
turned inwards. At the circumference of the cornea the posterior
 
elastic lamina becomes broken up into fibres. The most posterior of
 
these fibres pass in a radiating manner into the iris, and they form the
 
ligamentum pectinatum iridis, the intervals between the fibres of
 
which represent the spaces of the irido-corneal angle.
 
 
 
The layer of endothelium lines the posterior surface of the posterior
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE 1645
 
 
 
elastic lamina, and consists of one stratum of cells. It is continued
 
over the front of the iris, and into the spaces of the angle.
 
 
 
The cornea in the adult is non-vascular, except at the circumference, in which situation there are the conjunctival and sclerotic
 
capillaries, which terminate in loops. Being destitute of blood-vessels,
 
the nourishment of the cornea is maintained by the flow of lymph
 
through its surface. It is about 1 mm. thick, slightly more peripherally.
 
 
 
Nerve-supply.—The nerves are derived from the ciliary nerves,
 
and are very numerous. They enter the deep surface of the anterior
 
part of the sclera, and form a plexus round the corneo-scleral junction.
 
Offsets from this plexus enter the cornea, and form what is known
 
as the plexus annularis. From this plexus delicate offsets are given
 
off, which traverse the substance of the cornea and pass through
 
the anterior elastic lamina. They then give rise to a fine plexus upon
 
the surface of that lamina, called the subepithelial plexus. From
 
this plexus, in turn, minute fibrils are given off, which pass amongst
 
the cells of the conjunctival epithelium, and almost reach the surface,
 
forming an intra-epithelial plexus.
 
 
 
Pectinate Ligament of Iris.—It has been seen that the posterior
 
elastic lamina at its circumference breaks up into fibres. The most
 
posterior of these pass in a radiating manner into the iris, constitute
 
the ligamentum pectinatum iridis, and are covered by a prolongation
 
of the endothelial layer of the cornea.
 
 
 
Spaces of Irido-corneal Angle (or Spaces of Fontana).—These spaces
 
represent the irregular intervals which lie between the radiating fibres
 
of the pectinate ligament. They are lined by a prolongation of the
 
endothelial layer of the cornea, and they communicate internally with
 
the anterior chamber and the lymph-spaces within the iris, and
 
externally with the sinus venosus sclerae.
 
 
 
Sinus Venosus Sclerse.—This canal (formerly known as the canal
 
of Schlemm) is situated deeply in the sclerotic, close to the corneo-scleral
 
junction. It communicates internally with the anterior chamber
 
through the spaces of the irido-corneal angle, and externally with
 
anterior ciliary veins of the sclera. It encircles the outer margin of
 
the cornea, and has a little projecting rim of sclerotic on its deep
 
surface, called the ‘ scleral spur/ from which the ciliary muscle takes
 
 
 
origin.
 
 
 
Middle Coat.
 
 
 
1. Choroid Coat.— This is a very vascular, deeply pigmented tunic
 
of a dark brown colour, which lies between the sclera and the retina.
 
It extends over the posterior five-sixths of the eyeball, and reaches as
 
far forwards as the ora serrata of the retina. Anteriorly it is connected
 
with the circumference of the iris, and posteriorly it is pierced by the
 
optic nerve. Its outer surface is connected to the inner surface of the
 
sclera by means of the lamina fusca and its processes, as well as by
 
vessels and nerves which cross the ‘ perichoroidal lymph-space.
 
Its inner surface is in contact with the pigmentary- layer of the retina.
 
 
 
 
 
1646
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Structure.—The choroid coat consists of connective tissue, bloodvessels, and branched pigment-cells. It is composed of three layers,
 
which are as follows, from without inwards: (1) the lamina supra choroidea; (2) the choroid proper; and (3) the lamina basalis, or
 
membrane of Bruch.
 
 
 
The suprachoroid lamina is composed of delicate, non-vascular
 
lamellae, each of which is made up of elastic fibres arranged in a reticular
 
manner, and of branched pigment-cells.
 
 
 
The choroid proper consists principally of bloodvessels and pigmentcells supported by connective tissue. The bloodvessels are arranged
 
partly as arteries and veins, and partly as capillaries. The choroid
 
proper is therefore composed of two layers—external or lamina vasculosa, and internal or lamina chorio-capillaris.
 
 
 
The lamina vasculosa (arterio-venous layer) is composed of
 
(1) branches of the short ciliary group of the posterior ciliary arteries,
 
which pass forwards before they turn inwards to end in capillaries;
 
 
 
Suprachoroid Lamina
 
 
 
 
 
Arterio-Venous Layer
 
 
 
 
 
Membrana
 
Chorio-capillaris
 
 
 
Basal Lamina (Bruch’s Memb.)
 
 
 
Pigmentary Layer of the Retina
 
 
 
Fig. 1007.—Vertical Section of the Choroid Coat.
 
 
 
The pigmentary layer of the retina is also shown.
 
 
 
and (2) veins, which form the chief part of the lamina vasculosa,
 
and are called the vense vorticosae. These veins are very closely set,
 
and are arranged in a whorled manner. They ultimately converge
 
and form four or five vessels, which pierce the sclerotic nearly midway
 
between the optic entrance and the corneo-scleral junction at points
 
equally distant from each other. Scattered throughout the lamina
 
vasculosa are branched pigment-cells.
 
 
 
The lamina chorio-capillaris is composed of a plexus of capillary
 
bloodvessels, the arteries leading to it being derived from the short
 
ciliary arteries.
 
 
 
The lamina vasculosa and lamina chorio-capillaris are connected
 
by fine elastic fibres, which form what is known as the stratum intermedium.
 
 
 
The lamina basalis, or membrane of Bruch, is situated on the inner
 
surface of the lamina chorio-capillaris, which it separates from the
 
pigmentary layer of the retina. It is a very delicate membrane without any very definite structure.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1647
 
 
 
 
 
Tapetum. —This is present in certain animals. It lies between the lamina
 
vaseulosa and the lamina chorio-capillaris in the stratum intermedium, and it
 
gives rise to an iridescent or rainbow-like appearance. In some animals it is
 
fibrous in structure, and in others cellular.
 
 
 
2. Ciliary Body.—The ciliary body connects the anterior part of
 
the choroid to the circumference of the iris. It is composed of
 
(1) the orbicularis ciliaris, (2) the ciliary processes, and (3) the
 
ciliary muscle.
 
 
 
The orbicularis ciliaris, or ciliary ring, is a narrow zone which lies
 
immediately in front of the anterior part of the choroid, with which
 
it is continuous. In it are folds which are radially disposed, and it
 
separates the ciliary processes from the ora serrata of the retina.
 
 
 
The ciliary processes, about seventy in number, are infoldings
 
(Fig. 1005) of the anterior part of the choroid, and consist of the choroid
 
proper and the basal membrane (of Bruch). They constitute a series
 
 
 
 
 
Conjunctiva
 
 
 
Choroid
 
 
 
Sclera
 
 
 
 
 
Optic Nerve
 
 
 
 
 
 
 
Retina
 
 
 
 
 
Ciliary Body
 
Iris
 
 
 
Cornea
 
" Lens
 
 
 
'Anterior Chamber
 
Posterior Chamber
 
 
 
— Sinus Venosus Scleras
 
. Ora Serrata
 
 
 
 
 
Vitreous
 
 
 
 
 
Fig. 1008.—Diagram of Section through the Eyeball to show
 
the Main Layers mentioned in the Description.
 
 
 
S, S, suspensory ligament of lens.
 
 
 
 
 
of rays arranged in a circular manner, and converge as they pass inwards and forwards to the periphery of the crystalline lens on its
 
anterior aspect. They are somewhat conical in outline.. Their bases
 
or free extremities, which are round and prominent, lie behind the
 
circumference of the iris upon the anterior aspect of the periphery of
 
the crystalline lens. Their apices are connected with the orbicularis
 
ciliaris Anteriorly they are related to the posterior chamber of the
 
eyeball at its circumference. Posteriorly they are related to and
 
connected with the suspensory ligament of the lens.
 
 
 
Structure._The ciliary processes are similar in structure to the
 
 
 
choroid, but the pigment-cells are not so numerous. On their deep
 
or posterior surfaces the processes are covered by the ciliary part
 
of the retina, which is prolonged from the pigmentary layer of the
 
retina, and is continuous with the pars iridica retinae (uvea) on the
 
posterior surface of the iris.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1648
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
The arteries of the ciliary processes are derived from those of the
 
anterior part of the choroid, and from the anterior ciliary arteries.
 
The veins pass to those of the choroid.
 
 
 
Ciliary Muscle. —This muscle is composed of unstriped fibres. It
 
forms a greyish-white ring, about T V inch broad, which is situated at
 
the anterior part of the choroid opposite the ciliary processes. The
 
fibres are arranged in two sets—radial and circular. The radial
 
fibres arise from the calcar sclerae close to the corneo-scleral junction
 
and behind the sinus venosus of the sclera. From this origin they
 
pass backwards in a radiating manner, and are inserted into the
 
orbicularis ciliaris and the attached ends of the ciliary processes. The
 
circular fibres form a ring around the circumference of the iris internal
 
to the radial fibres.
 
 
 
 
 
Pupil
 
 
 
 
 
 
 
Fig. 1009.—The Iris and Ciliary Processes (Posterior View)
 
 
 
(Hirschfeld and Leveille).
 
 
 
The ciliary muscle is supplied by the short ciliary nerves, which are
 
branches of the ciliary ganglion, and derive their fibres from the
 
motor oculi nerve.
 
 
 
Action. —The ciliary muscle is the muscle of accommodation , and
 
adjusts the eye to the vision of near objects. When it contracts it
 
draws forwards the choroid and the ciliary processes; the suspensory
 
ligament of the crystalline lens is thereby relaxed, and, as a consequence, the anterior surface of the lens is rendered convex.
 
 
 
The circular fibres of the ciliary muscle are well developed in
 
cases of hypermetropia, but are deficient in cases of myopia.
 
 
 
3. Iris. —The iris forms the anterior part of the middle coat of the
 
eyeball. It is a coloured contractile diaphragm, which is suspended
 
in the aqueous humour between the cornea and the crystalline lens.
 
It is perforated by an almost circular aperture, called the pupil, which
 
is situated slightly to the nasal or inner side of its centre, and serves
 
for the transmission of light. The margin which surrounds the pupil
 
is known as the pupillary margin. Its circumference is continuous
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1649
 
 
 
with the ciliary body, and is connected with the posterior elastic
 
lamina of the cornea by means of the ligamentum pectinatum iridis
 
 
 
 
 
Anterior Wall of Capsule of Lens..(I
 
 
 
 
 
Sphincter Pupillae ...
 
 
 
 
 
Membrane
 
of Descemet —
 
 
 
 
 
Epithelium .
 
of Cornea
 
 
 
 
 
Sinus Venosus
 
Scleras
 
 
 
 
 
Suspensory
 
Ligament
 
Middle Portion of
 
Suspensory Ligament
 
 
 
Posterior Portion of
 
Suspensory Ligament
 
 
 
 
 
Margin of Cornea
 
 
 
Conjunctiva —
 
 
 
 
 
 
 
Ciliary Muscle
 
"Radiating Fibres)
 
 
 
 
 
Fig. ioio.—Meridional Section through the Anterior Portion of
 
 
 
the Eye (magnified 16X1) (Fuchs).
 
 
 
C.P., C.P., zonular spaces.
 
 
 
at the iridial angle. The circumference is known as the ciliary margin.
 
The surfaces of the iris are anterior and posterior. The anterior
 
 
 
TO4
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1650
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
surface is directed towards the cornea. Its colour varies in different
 
individuals, and it presents a striated appearance, the striae converging
 
towards the margin of the pupil, and being produced by the underlying vessels. The posterior surface is directed towards the crystalline
 
lens and ciliary processes. It has a purple colour, and is covered by
 
two layers of columnar epithelium, the cells of which contain dark
 
pigment. These two layers of pigmented cells constitute the pars
 
iridica retinae (uvea), which is continuous with the pars ciliaris retinae.
 
 
 
_ The iris divides the space between the cornea and the crystalline lens
 
into two compartments, the anterior chamber and posterior chamber,
 
both of which contain the aqueous humour.
 
 
 
Structure. —The component parts of the iris are (1) a layer of
 
endothelium; (2) a connective-tissue stroma, with branched pigmentcells; (3) muscular tissue; and (4) pigment.
 
 
 
The layer of endothelium covers the anterior surface of the iris,
 
and is continuous with the endothelium which lines the posterior
 
elastic lamina of the cornea.
 
 
 
 
 
Long Ciliary Artery
 
 
 
 
 
 
 
Fig. ioii.—The Arteries of the Choroid and Iris (Lateral View).
 
 
 
The connective-tissue stroma is composed of fibres which for the
 
most part pass in a radiating manner towards the pupillary margin.
 
Some, however, are disposed circularly at the ciliary margin. They
 
support the bloodvessels and nerves, and scattered between their
 
bundles there are branched cells. These cells contain pigment in darkcoloured eyes, but in blue eyes there is little pigment here.
 
 
 
The muscular tissue is of the unstriped variety, and its fibres are
 
arranged in two sets, circular and radiating. The circular fibres form
 
a ring round the pupil, and are nearer the posterior surface than the
 
anterior. They are known as the sphincter pupillse. The radiating
 
fibres converge from the ciliary margin of the iris towards the pupillary
 
margin, where they blend with the circular fibres. The radiating
 
fibres constitute the dilator pupillse. Some authorities regard the
 
radiating fibres as elastic, and not muscular.
 
 
 
The pigment of the iris is variously situated, according to the
 
colour of the eye. In the eyes of albinos there is no pigment. In
 
other eyes pigment is contained in the cells of the two layers of columnar
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1651
 
 
 
epithelium which line the posterior surface of the iris, and form the
 
pars iridica retinae (uvea). In blue eyes the pigment is largely confined to this region, but in other coloured eyes it is also present in the
 
branched cells of the connective-tissue stroma.
 
 
 
Blood-supply—Arteries. —The arteries of the iris are derived from
 
(1) the long ciliary, and (2) the anterior ciliary vessels.
 
 
 
The long ciliary arteries are two in number, and belong to the
 
posterior ciliary group of branches from the ophthalmic artery. They
 
pierce the back part of the sclera, one on each side of the optic
 
nerve, and pass forwards between the sclera and the choroid towards
 
the ciliary margin of the iris. Here each vessel divides into two
 
branches, upper and lower, which anastomose with those of the
 
opposite side to form an arterial ring round the ciliary margin of the
 
iris, called the circuius arteriosus major. This ring is joined by some
 
of the anterior ciliary arteries, and it gives offsets to the ciliary muscle
 
 
 
 
 
Pupil
 
 
 
; Iris
 
 
 
 
 
 
 
Fig. 1012. —The Choroid and Iris, showing the Ven,e Vorticose
 
and Ciliary Nerves (after Hirschfeld and Leveille).
 
 
 
The sclera and cornea have been removed.
 
 
 
and iris. The branches which enter the iris are supported by the
 
connective-tissue stroma, and converge towards the pupillary margin,
 
near which they form by their anastomoses another arterial ring,'
 
called the circulus minor.
 
 
 
The anterior ciliary arteries are about six in number, and are
 
derived from the muscular and lacrimal branches of the ophthalmic
 
artery. They are of small size, and pierce the anterior part of the
 
sclera close to the corneo-scleral junction. Some of them supply the
 
ciliary processes, and others join the circulus major (see Fig. ion).
 
 
 
The veins of the iris accompany the arteries, and are in communication with the sinus venosus sclerse.
 
 
 
Nerves of the Choroid Coat and Iris. —These are derived from the
 
ciliary nerves, short and long, the former coming from the ciliary
 
ganglion, and the latter from the naso-ciliary branch of the ophthalmic
 
or first division of the fifth cranial nerve. They are about sixteen
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1652
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
in number, and pierce the back part of the sclera around the optic
 
nerve. They then pass forwards between the sclerotic and choroid,
 
giving branches to the latter coat, which become disposed in a plexiform manner amongst the bloodvessels. Having reached the corneoscleral junction, the nerves enter the ciliary muscle, in which they form
 
a plexus. From this plexus branches enter the iris at the ciliary
 
margin. These branches accompany the vessels, and by their subdivisions and communications they form a copious plexus of nonmedullated fibres in the connective-tissue stroma of the iris. The
 
sphincter pupillse is supplied by fibres which are derived from the oculomotor or third cranial nerve by means of the motor root of the ciliary
 
ganglion. The dilator pupillae is supplied by fibres which may be
 
traced to the second thoracic ganglion through the sympathetic root
 
of the ciliary ganglion (see p. 1637).
 
 
 
Membrana Pupillaris. —During intra-uterine life the pupil is closed by a
 
delicate membrane, called the membrana pupillaris. This disappears shortly
 
before birth, but remnants of it are sometimes found.
 
 
 
 
 
Internal Coat.
 
 
 
Retina.—The retina is the internal or nervous tunic of the eyeball. It is soft in consistence, translucent, and of a pinkish colour.
 
Its internal surface is in contact with the hyaloid membrane, which
 
 
 
 
 
 
 
Fig. 1013.—The Posterior Portion of the Right Retina
 
 
 
(Anterior View).
 
 
 
 
 
encloses the vitreous body, and its external surface is in contact with
 
the choroid coat. Posteriorly it receives the fibres of the optic
 
nerve. Anteriorly it extends almost to the ciliary body, where there
 
is a notched border, called the ora serrata. Here its nervous elements
 
cease, but its pigmentary layer is continued over the deep or posterior
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1653
 
 
 
 
 
surfaces of the ciliary processes on to the posterior surface of the iris,
 
forming, with the addition of a layer of columnar epithelial cells,
 
the pars ciliaris retinae and pars iridica retinae (uvea) respectively.
 
The retina diminishes in thickness from behind forwards.
 
 
 
The external surface is formed by a stratum of hexagonal pigmentcells, which send processes into the adjacent layer. When the choroid
 
is separated from the retina these processes are torn, and the stratum
 
of pigment-cells remains attached to the choroid, being apparently
 
a part of it. The pigmentary layer, however, really belongs to the
 
retina.
 
 
 
The internal surface shows, in the line of the visual axis of the
 
eyeball, the macula lutea or yellow spot, where vision is most distinct.
 
This spot is transversely oval, and measures about X V inch from side
 
 
 
 
 
 
 
Fig. 1014.—Longitudinal Section through the Head of the Optic
 
 
 
Nerve (14X1)
 
 
 
 
 
r. Retina
 
 
 
b. Centre of Porus Opticus
 
ch. Choroid
 
 
 
s. Sclera
 
 
 
so. Outer Part of Sclera
 
si. Inner part of Sclera
 
ci. Ciliary Artery (in longitudinal section)
 
sd. Subdural Space
 
 
 
nasal, Medial Side
 
 
 
 
 
(Fuchs).
 
 
 
sa. Subarachnoid Space
 
n. Bundles of Nerve-fibres
 
se. Septa between the Nerve-bundles
 
a. Arteria Centralis Retinae
 
v. Vena Centralis Retinae
 
p. Sheath formed by Pia Mater
 
ar. Sheath formed by Arachnoid
 
du. Sheath formed by Dura Mater
 
 
 
temporal, Lateral Side
 
 
 
 
 
to side. At its centre is a slight depression, called the fovea centralis.
 
In this situation the retina is thinnest, and the dark colour of the
 
hexagonal pigment-cells is visible through it, giving it the appearance
 
of a foramen. About inch to the inner side of the posterior pole
 
of the eyeball, and about iucb below its level, is the porus opticus,
 
or optic disc. This is circular in outline, and its circumference is
 
slightly elevated. It is the point of entrance of the fibres of the optic
 
nerve, and the centre of the disc is pierced by the arteria centralis
 
retinae which immediately divides into two branches upper and
 
lower. * The optic disc consists entirely of nerve-fibres, and is known
 
as the ‘ blind spot,’ vision being absent in this situation.
 
 
 
Structure of the Retina.— The retina consists of eight superimposed layers, seven of which are nervous and one pigmentary.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
1654
 
 
 
 
 
In addition to these, there are sustentacular fibres. The eight layers
 
are as follows, from within outwards:
 
 
 
 
 
1. Stratum opticum, or layer of nerve-fibres.
 
 
 
2. Ganglionic layer, or layer of nerve-cells.
 
 
 
3. Inner plexiform (inner molecular) layer.
 
 
 
4. Inner nuclear or granular layer.
 
 
 
5. Outer plexiform (outer molecular) layer.
 
 
 
6. Outer nuclear or granular layer.
 
 
 
7. Layer of rods and cones.
 
 
 
8. Pigmentary layer.
 
 
 
 
 
 
 
Pigmentary Layer
 
 
 
 
 
1 Layer of Rods and Cones
 
 
 
 
 
A. Membrana Limitans Externa
 
 
 
 
 
> Outer Nuclear Layer
 
 
 
 
 
„_Outer Plexiform Layer
 
 
 
 
 
. Inner Nuclear Layer
 
 
 
 
 
In addition to the foregoing layers, there are two very delicate
 
membranes, which really belong to the sustentacular fibres of the
 
 
 
retina, but are known
 
as the membrana limitans interna and externa. The membrana
 
limitans interna covers
 
the retina on its internal surface, and the
 
membrana limitans externa intervenes between the outer nuclear
 
layer and that of the
 
rods and cones. The
 
layers of the retina
 
are supported by fibres
 
called the sustentacular
 
fibres.
 
 
 
1. Stratum Opticum.
 
 
 
—This layer consists of
 
the fibres of the optic
 
nerve, and it extends
 
from the optic disc to
 
the ora serrata. The
 
fibres are non-medullated, and are chiefly
 
centripetal, but some
 
are centrifugal. The
 
 
 
centripetal fibres arise
 
Fus ioi 5. Diagrammatic Section of the Human mainly as the axons of
 
 
 
• R =mIT LTZE) COPIED FR0M QUAIN ’ S the “ lls of the S an 8
 
lionic layer. The centrifugal fibres pass towards the inner plexiform and inner nuclear
 
layers.
 
 
 
2. Ganglionic Layer.—This consists of large, somewhat flaskshaped, multipolar ganglion-cells, which for the most part form a
 
single layer. In the macula lutea, however, they form several layers.
 
 
 
 
 
> Inner Plexiform Layer
 
 
 
 
 
Layer of Nerve-cells
 
(Ganglionic Layer)
 
 
 
I Layer of Nerve-fibres
 
 
 
Membrana Limitans Interna
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1655
 
 
 
 
 
The round ends of the cells rest upon the stratum opticum, and from
 
each of these ends an axon is given off, which enters the stratum
 
opticum obliquely, and forms one of its component fibres. The
 
tapering end of each cell sends off several dendrites, which enter the
 
inner plexiform layer, within which they arborize.
 
 
 
3. Inner Plexiform (Inner Molecular) Layer contains the arborizations of the dendrites of (1) the cells of the ganglionic layer, and
 
(2) the bipolar cells of the inner nuclear layer. The intercommunications between these two sets of dendrites give rise to five strata, according to Ramon y Cajal. Besides these, there are the arborizations. of
 
the processes of the spongioblasts of the inner nuclear layer, which
 
are likewise arranged in strata.
 
 
 
4. Inner Nuclear or Granular Layer.—This layer consists of cells
 
which are arranged in three groups: (1) bipolar cells, (2) horizontal
 
cells, and (3) spongioblasts, or amacrine cells. The bipolar cells are
 
the most numerous, and are nucleated. Each cell gives off two processes—internal and external. The internal processes of the cells enter
 
the inner plexiform layer, and end at different levels in arborizations.
 
The external processes pass into the outer plexiform layer, and form
 
arborizations in its outermost part, which are closely related to the
 
terminal parts of the rods and cones of the bacillary layer. According to Cajal, the bipolar cells are of two kinds—rod-bipolars and conebipolars. The external processes of the rod-bipolars ramify round the
 
terminal parts of the rod-fibres, and the internal processes arborize
 
round the cells of the ganglionic layer. The external processes of
 
the cone-bipolars form horizontal arborizations round the ends of
 
the cone-fibres, and the internal processes terminate in arborizations
 
in the inner plexiform layer at different levels.
 
 
 
The horizontal cells occupy the outer part of the inner nuclear
 
layer. Their dendrites enter the outer plexiform layer, and come
 
into relation with the terminal parts of the cone-fibres, whilst their
 
 
 
axons run in a horizontal direction. .
 
 
 
The spongioblasts are situated in the innermost part of the inner
 
nuclear layer. They are destitute of axons, and ha\ e been called
 
amacrine cells, because each cell is ‘ without a long fibre or process.
 
Their dendrites enter the inner plexiform layer, and end in arboriza
 
 
 
tions, which are arranged in strata.
 
 
 
=; Outer Plexiform (Outer Molecular) Layer.—This layer is composed of the following structures: (i) the external processes of the
 
rod-bipolars and cone-bipolars of the inner nuclear layer; (2) the
 
dendrites of the horizontal cells of the inner nuclear layer; and (3) the
 
terminal parts of the rod-fibres, and filaments from the foot-plates
 
 
 
of the cone-fibres. ,
 
 
 
6 Outer Nuclear or Granular Layer.—This consists of granules,
 
 
 
which are of two kinds—rod-granules and cone-granules. The rodgranules are the more numerous, and are oval enlargements m the course
 
of the rod-fibres, as these pass to the outer plexiform layer'• Each
 
rod-fibre has only one rod-granule, and the granules lie at different
 
 
 
 
 
1656
 
 
 
 
 
A MANUAT, OF ANATOMY
 
 
 
 
 
levels. Each granule has a nucleus, which has transverse striations,
 
there being at least two clear bands. The external process of each
 
rod-granule is continuous with one of the rods of the bacillary layer,
 
and the internal process passes into the outer plexiform layer, where
 
it comes into relation with the arborizations of the external process of
 
a rod-bipolar.
 
 
 
The cone-granules are larger than the rod-granules, but not so
 
numerous, and each contains an oval nucleus. Situated in the outermost part of the outer nuclear layer, they lie close to the membrana
 
limitans externa. The outer end of each granule is continuous with
 
one of the cones of the bacillary layer. The inner end is prolonged
 
into a cone-fibre, which passes into the outermost part of the outer
 
 
 
 
 
 
 
Fig. 1016. —Scheme of the Horizontal Cells and Spongioblasts of the
 
 
 
Retina (Ramon y Cajal).
 
 
 
 
 
A. Rod-fibres
 
 
 
B. Cone-fibres
 
 
 
1. Outer Plexiform Layer
 
a, b. Horizontal Cells, with arborizations
 
c. Horizontal Cell, with deep processes
 
 
 
 
 
2. Inner Plexiform Layer
 
/» S, h , f Spongioblasts extending to
 
j, l. 1 different depths
 
m, n. Spongioblasts with diffuse processes
 
o. Ganglionic Nerve-cell
 
 
 
 
 
plexiform layer, where it expands into a foot-plate, from which filaments are given off. These filaments come into relation with the
 
arborizations of the external process of a cone-bipolar cell.
 
 
 
7. Layer of Rods and Cones consists of rods and cones, the former
 
being cylindrical, and the latter flask-shaped. The rods are much
 
more numerous, longer, and narrower than the cones, and both are
 
placed perpendicularly.
 
 
 
Each rod and cone consists of two segments—outer and inner.
 
In the case of the rods the two segments are of almost equal length the
 
inner segment being rather larger than the outer. The outer segment
 
is the only seat of the colouring matter known as visual purple or
 
rhodopsin In the case of the flask-shaped cones, the inner segment
 
of each forms two-thirds of the cone, and is of large size; whilst the
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1657
 
 
 
outer forms one-third, is narrow, and represents the tapering part of
 
the flask. The outer segments of both rods and cones have faint
 
transverse striations. The inner segments of both are subdivided.
 
The outer part is composed of delicate fibrils longitudinally arranged,
 
and therefore presents a longitudinally striated appearance. The
 
inner part is faintly granular. The rods and cones are continued at
 
their inner ends through the membrana limitans externa into the
 
rod-fibres and cone-fibres, which belong to the outer nuclear layer.
 
The outer ends of the rods project into the pigmentary layer.
 
 
 
8 . Pigmentary Layer.—The most external layer of the retina is
 
in close contact with the choroid coat. It consists of a single layer
 
of hexagonal epithelial cells, which contain pigment. The deep
 
surfaces of the cells
 
give off processes which
 
extend into the intervals between the outer
 
ends of the rods and
 
 
 
 
 
 
 
Layer of Rods and Cones
 
 
 
 
 
Membrana Limitans Externa
 
 
 
 
 
Outer Nuclear Layer
 
 
 
 
 
Outer Plexiform Layer
 
Inner Nuclear Layer
 
 
 
 
 
Inne’ Plexiform Layer
 
 
 
 
 
Ganglionic Layer
 
 
 
 
 
1 1 Nerve-fibre Layer
 
■/.Membrana Limitans Interna
 
 
 
Fig. 1017.—Section of the Retina as seen
 
 
 
UNDER THE MICROSCOPE (MAGNIFIED).
 
 
 
 
 
 
 
 
 
 
 
cones.
 
 
 
Sustentacular Fibres
 
(or Fibres of Muller).—
 
 
 
These fibres form the
 
supporting tissue of the
 
retina, and extend from
 
its internal surface to
 
the boundary-line between the outer nuclear
 
layer and the layer of
 
rods and cones. The
 
inner ends of the fibres
 
are expanded, and blend
 
at their edges to present
 
the appearance of a
 
distinct retinal layer,
 
which is called the membrana limitans interna. Their outer ends,
 
which are very numerous owing to the breaking up of the fibres,
 
also expand and form the membrana limitans externa, which lies
 
between the outer nuclear layer and the layer of rods and cones.
 
(The membrana limitans interna and externa are sometimes considered layers of the retina, under which circumstances the retinal
 
layers would be ten in number, instead of eight.) From the membrana
 
limitans externa delicate offsets enter the layer of rods and cones,
 
in the innermost part of which they form fibre-baskets in connection
 
with the deep ends of the rods and cones. As the sustentacular fibres
 
pass through the inner nuclear layer each has an oval nucleus, which
 
contains a nucleolus. This nucleus is variously described as being
 
situated on one side of the fibre, or as involving its whole circumference. Throughout their course the sustentacular fibres give off
 
lateral offsets, which increase in number from within outwards.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1658
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Structure of the Macula Lutea and Fovea Centralis.—The chief
 
structural characters of the macula lutea and fovea centralis may
 
be stated in the following tabular manner:
 
 
 
 
 
Macula Lutea.
 
 
 
1. Cones only.
 
 
 
2. Outer nuclear layer has only cone
 
fibres disposed obliquely.
 
 
 
3. Ganglionic layer very thick, cells being
 
 
 
several layers deep.
 
 
 
4. Stratum opticum not continuously
 
 
 
disposed.
 
 
 
B
 
 
 
 
 
Fovea Centralis.
 
 
 
1. Thinnest part of the retina.
 
 
 
2. Pigmentary layer thick.
 
 
 
3. Cones only.
 
 
 
4. Outer nuclear layer has only
 
 
 
cone-fibres.
 
 
 
5. Ganglionic layer absent.
 
 
 
6. Stratum opticum absent.
 
 
 
A
 
 
 
 
 
Membrana Limitansv
 
Externa N, “
 
 
 
 
 
Fibrous Basket-work
 
 
 
 
 
Outer Plexiform
 
Layer
 
 
 
 
 
Nucleus of one of
 
Sustentacular Fibres
 
 
 
 
 
Inner Plexiform_
 
 
 
Layer
 
 
 
 
 
Sustentacular Fibres'
 
Limitans Interna 1 '
 
Membrana
 
 
 
 
 
 
 
Centrifugal Nerve-fibre
 
 
 
 
 
Rods and Cones
 
 
 
 
 
Outer Nuclear
 
Layer
 
 
 
 
 
Subepithelial
 
 
 
Ganglion-cell
 
 
 
Stellate Ganglioncell
 
 
 
Bipolar Q.anglioncell
 
 
 
Multipolar
 
 
 
Ganglion-cell
 
 
 
 
 
Multipolar
 
Ganglion-cell
 
Layer of Nervefibres
 
 
 
 
 
Fig. 1018.—Diagram of the Elements of the Retina (Wiedersheim,
 
 
 
AFTER PH. StoHR).
 
 
 
A, nervous elements; B, supporting elements.
 
 
 
 
 
Structure of the Ora Serrata.—At the ora serrata the nervous
 
elements of the retina end, and its pigmentary layer is continued over
 
the deep or posterior surfaces of the ciliary processes. Here is added
 
to its deep or posterior surface a layer of columnar epithelial cells,
 
and the two layers form the pars ciliaris retinas, which is continued
 
into the pars iridica retinae (uvea). In the latter the cells of both
 
layers are pigmented.
 
 
 
Blood-supply of the Retina.—The retina is supplied with blood by
 
the arteria centralis retinae, a branch of the ophthalmic artery. Within
 
the orbit the artery pierces the under aspect of the optic nerve a little
 
behind the eyeball, and passes forwards in the centre of the nerve.
 
At the centre of the optic disc it divides into two branches, upper
 
and lower. Each of these breaks up into two branches, nasal or medial,
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1659
 
 
 
 
 
and temporal or lateral. The temporal branches keep clear of the
 
macula lutea, but give small twigs to it, which, however, do not enter
 
the fovea centralis, this part being non-vascular. As the branches
 
pass inwards and outwards respectively towards the periphery of the
 
retina they ramify freely, and end at last in capillary networks.
 
The arteries do not extend farther outwards than the inner nuclear
 
layer. No anastomoses take place between the branches of the arteria
 
centralis retinae.
 
 
 
 
 
 
 
Fig. 1019._Scheme of the Retina, showing the Connection between
 
 
 
the Layer of Rods and Cones and the Ganglionic Layer (Ramon
 
 
 
 
 
y Cajal).
 
 
 
A. Layer of Rods and Cones
 
 
 
B. Outer Nuclear Layer
 
 
 
C. Outer Plexiform Layer
 
 
 
E. Inner Nuclear Layer
 
 
 
F. Inner Plexiform Layer
 
 
 
G. Ganglionic Layer
 
 
 
H. Layer of Nerve-fibres
 
M. Sustentacular fibre
 
 
 
a. Rods
 
 
 
b. Cones
 
 
 
c. Granule of Cones
 
 
 
d. Granule of Rods
 
 
 
 
 
e. Bipolar Cells of Rods
 
 
 
f. Bipolar Cells of Cones
 
 
 
g, h, i, \ Ganglionic Corpuscles ramifying at different
 
j, k. f levels in Inner Plexiform Layer
 
r, r'. Deep arborizations of Bipolar Cells
 
 
 
s. Centrifugal Nerve-fibre
 
 
 
t. Nucleus of Sustentacular Fibre
 
 
 
X. Deep ends of Rod-fibres amongst superficial
 
arborizations of Bipolar Cells
 
Z. Meeting of arborizations of Cones and Bipolar
 
Cells
 
 
 
 
 
In the foetus the arteria centralis retinae sends a branch to the
 
posterior part of the capsule of the crystalline lens, which reaches it
 
through the ‘ canal of Cloquet in the vitreous body.
 
 
 
The veins are ultimately collected into two vessels, upper and
 
lower, which pass through the optic disc, one above and the other
 
below' the artery. They then form one vessel which opens into the
 
superior ophthalmic vein. The veins of the retina are destitute of
 
muscular tissue, the wall of each being formed by a single layer of
 
endothelial cells, external to which there is a perivascular lymph
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
i66o
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
space, this in turn being limited by another layer of endothelial cells.
 
These lymph-spaces are in communication with those of the optic
 
nerve.
 
 
 
Relation of the Retinal Layers to One Another.—The only two
 
layers which are in direct continuity are the stratum opticum and
 
ganglionic layer, some fibres of the former being the axons of the
 
cells of the latter. As regards most of the strata, the constituent
 
elements of successive layers are brought into communication by
 
means of the interlacements which take place between the arborizations formed by their various processes. These interlacements occur
 
in the inner and outer plexiform layers.
 
 
 
 
 
Levator Palpebrae Superioris
 
 
 
Hyaloid Canal >
 
 
 
(Canal of Cloquet)
 
 
 
 
 
Hyaloid Membrane
 
 
 
 
 
Retina
 
 
 
 
 
Sinus Venosus
 
S clerae
 
 
 
Posterior
 
Chamber
 
 
 
Anterior
 
Chamber
 
 
 
 
 
Choroid
 
 
 
 
 
Rectus Superior
 
s „ Sclera
 
 
 
 
 
Arteria
 
 
 
, l /Centralis
 
*' '■ / Retinae
 
 
 
 
 
 
 
Cornea
 
 
 
Ciliary / y.
 
 
 
Processes'
 
 
 
Zonular Space
 
 
 
 
 
Rectus Inferior
 
 
 
 
 
Fornix Conjunctivas
 
 
 
Fig. 1020.—Vertical Sagittal Section of the Eye and its
 
Appendages (Hirschfeld and Leveille).
 
 
 
 
 
In the inner plexiform layer there are several strata of interlacements, by means of which the dendrites of the cells of the ganglionic
 
layer are brought into communication with the internal processes of
 
the bipolar cells of the inner nuclear layer. In the outer plexi orm
 
layer there is a free intermingling between the external processes of
 
the bipolar cells of the inner nuclear layer and the rod-fibres and conefibres.
 
 
 
Nerve-cells of the Retina.—These are arranged in three strata,
 
and communicate with one another through interlacing arborizations.
 
The outermost stratum consists of the rods and cones; the middle
 
stratum is formed by the bipolar cells; and the innermost stratum
 
represents the cells of the ganglionic layer. The axons of the gang
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1661
 
 
 
 
 
lionic cells enter the stratum opticum as centripetal fibres, which pass
 
in the optic nerve to the brain. The centrifugal fibres of the stratum
 
opticum ramify in the inner plexiform or inner nuclear layer.
 
 
 
Refracting Media.
 
 
 
Aqueous Humour and Chambers of the Eye.—The aqueous humour
 
occupies the space between the cornea and the front of the crystalline
 
lens, which is divided by the iris into two chambers, anterior and
 
posterior. It is a clear fluid having an alkaline reaction, and is
 
composed of H ? 0 , holding in solution a very small amount of sodium
 
chloride and traces of albumen.
 
 
 
The anterior chamber is bounded anteriorly by the cornea, and
 
posteriorly by the iris and the central portion of the crystalline lens
 
enclosed within its capsule. The anterior
 
chamber communicates with the irido-corneal
 
spaces, through them with the sinus venosus
 
sclerae, and through this canal with the veins
 
of the sclera.
 
 
 
The posterior chamber, which is of limited
 
extent, is bounded anteriorly by the iris, and
 
posteriorly by the peripheral part of the
 
crystalline lens and its suspensory ligament,
 
and by the ciliary processes. The anterior and
 
posterior chambers communicate with each
 
other through the pupil; with lymph-spaces in
 
the iris; and through the latter spaces with
 
the perichoroidal lymph-space.
 
 
 
Crystalline Lens.—The crystalline lens is
 
situated directly behind the pupil and iris, from
 
which latter it is separated by the posterior
 
chamber. It is a solid, transparent, biconvex
 
disc, the posterior surface being more convex
 
than the anterior, and is enclosed within a A ’ 0 fi n br e e 4° e f ) . th ^°L ( man
 
homogeneous, transparent envelope, called the fibres (seen on end).
 
capsule of the lens. The centre of the anterior
 
 
 
surface is called the anterior pole, and that of the posterior surface
 
the posterior pole. The line connecting these two poles constitutes
 
the axis of the lens, and a line surrounding the periphery represents
 
the equator. The transverse measurement of the lens, is about
 
•it inch, and its axis measures about inch. The . anterior surface
 
at its central part faces the pupil. External to this, the pupillary
 
margin of the iris rests upon it, and external to this again is the
 
posterior chamber, with part of the aqueous humour. The posterior
 
surface is received into the ‘ patellar fossa on the anterior aspect
 
of the vitreous body. The periphery is related to the suspensory
 
ligament, the zonular spaces present in this ligament, and the ciliary
 
processes. From the anterior and posterior poles delicate lines radiate
 
 
 
 
 
 
 
Fig. 1021.—Fibres of
 
the Crystalline
 
Lens (highly magnified) (after Kolliker).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1662
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
towards the equator. In early life these are three on each surface.
 
Those on the posterior surface form an inverted while those on
 
the anterior form an erect Y. These lines represent the free margins
 
of septa within the lens upon which the ends of the lens-fibres terminate.
 
 
 
Structure.—The lens is laminar in structure. The outer laminae
 
are soft in consistence, but the succeeding ones gradually become
 
firmer, and the central portion, which constitutes the nucleus, is
 
very firm and hard. The laminae are arranged concentrically, and
 
after boiling or immersion in alcohol they may be peeled off, like
 
the coats of an onion. The fibres of which the laminae are composed
 
terminate upon septa within the lens, of which the radiating lines on
 
the surfaces, already referred to, are the free margins. The concentric laminae are therefore not continuous all round, but are split
 
up along these lines. The lens-fibres, which are disposed in a curved
 
manner, are of small size, and have serrated edges, which fit closely
 
to each other. In transverse section the fibres appear as hexagonal
 
prisms. The fibres are the elongated cells which line the posterior
 
part of the ectodermal vesicle (lens vesicle) from which the lens is
 
developed. In early life each fibre has a nucleus, but after the lens has
 
attained its full development only the outermost fibres are nucleated.
 
 
 
Capsule of the Lens.—This is a transparent, homogeneous, elastic
 
and brittle membrane, which surrounds and encloses the lens. Its
 
anterior wall is thicker and more elastic than the posterior. In the
 
adult the lens and its capsule are non-vascular, but in the foetus they
 
receive the hyaloid branch of the arteria centralis retinae, which reaches
 
it through the hyaloid canal in the vitreous body.
 
 
 
Epithelium of the Lens.—The posterior surface of the lens is devoid
 
of epithelium, and is in direct contact with the posterior wall of the
 
capsule. The anterior surface is covered by a single layer of columnar
 
cells, which intervenes between the anterior surface and the anterior
 
wall of the capsule. Towards the equator these cells become elongated,
 
and pass into short fibres, which become continuous with the superficial
 
lens-fibres.
 
 
 
Crystalline Lens at Different Ages.—The characters of the lens at
 
different ages are as follows:
 
 
 
 
 
Foetal Lens.
 
 
 
Almost spherical.
 
Pinkish colour.
 
Semitransparent.
 
Soft in consistence.
 
 
 
 
 
Adult Lens.
 
 
 
Biconvex
 
 
 
Colourless.
 
 
 
Transparent.
 
 
 
Firm in consistence.
 
 
 
 
 
Lens in Old Age.
 
 
 
Flattened.
 
 
 
Amber colour.
 
 
 
Opaque, more or less.
 
Very firm in consistence.
 
 
 
 
 
Vitreous Body.—This body occupies about four-fifths of the space
 
within the eyeball, and is situated between the crystalline lens and the
 
retina. It is transparent and gelatinous, and is composed of water,
 
holding in solution a small quantity of sodium chloride and albuminous
 
matter. It is surrounded by a transparent, homogeneous envelope,
 
called the hyaloid membrane. This membrane is in contact with the
 
retina, except anteriorly, where there is an excavation called the fossa
 
 
 
 
 
/
 
 
 
 
 
THE EYE 1663
 
 
 
patellaris , into which the posterior surface of the crystalline lens is
 
received.
 
 
 
 
 
Anterior Wall of Capsule of Lens __I
 
 
 
 
 
Sphincter Pupillae_
 
 
 
 
 
Membrane
 
of Descemet
 
 
 
 
 
Epithelium
 
of Cornea
 
 
 
 
 
Suspensory
 
Ligament
 
Middle Portion of
 
Suspensory Ligament
 
 
 
Posterior Portion of
 
Suspensory Ligament
 
 
 
 
 
Sinus Venosus
 
Sclera
 
 
 
Margin of
 
Cornea
 
 
 
 
 
Conjunctiva
 
 
 
 
 
Ciliary Muscle
 
'Radiating Fibres)
 
 
 
 
 
Fig. 1022.—Meridional Section through the Anterior Portion of
 
 
 
the Eye (magnified 16X1) (Fuchs).
 
 
 
C.P., C.P., zonular spaces.
 
 
 
 
 
Towards its circumference the vitreous body is laminated, the
 
laminae being arranged concentrically. Laminae are also said to radiate
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1664
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
from its antero-posterior axis towards the circumference. Scattered
 
throughout the vitreous body there are some amoeboid corpuscles,
 
and it is traversed from behind forwards by a minute passage called
 
the hyaloid canal (canal of Cloquet, canal of Stilling). This extends
 
from the centre of the optic disc to the posterior wall of the capsule
 
of the lens, and posteriorly it communicates with the lymph-spaces of
 
the optic nerve. In the foetus the canal transmits a branch of the
 
arteria centralis retinae, called the hyaloid artery , which supplies the lens.
 
 
 
No vessels enter the vitreous body, its nutrition being derived
 
from the vessels of the retina and ciliary processes.
 
 
 
Zonula ciliaris, or zonule of Zinn, is the thickened portion of the
 
hyaloid membrane which is situated in front of the ora serrata of the
 
retina. From this point it extends inwards behind the ciliary processes towards the periphery of the crystalline lens. Behind the
 
ciliary processes are radial folds with intervening depressions. The
 
depressions receive the ciliary processes, and the radial folds are
 
separated from the intervals between the ciliary processes by lymphspaces, which communicate with the posterior chamber of the eye.
 
 
 
Suspensory Ligament of the Lens, and Zonular Spaces.—The ciliary
 
zonule, as it approaches the periphery of the lens, divides into three
 
layers—posterior, middle, and anterior. The posterior layer lines the
 
fossa patellaris in front of the hyaloid membrane. The middle layer
 
consists of a few scattered fibres which pass to the equator of the lens.
 
The anterior layer is the thickest, and forms the suspensory ligament
 
of the lens, which is attached to the anterior wall of its capsule not
 
far from the equator (see Fig. 1022). When the radiating fibres of
 
the ciliary muscle contract the suspensory ligament is relaxed, and
 
the convexity of the anterior surface of the lens is increased.
 
 
 
Behind the suspensory ligament of the lens there is a sacculated
 
lymph-space, called the zonular space, which surrounds the equator
 
of the lens.
 
 
 
Development of the Eye.
 
 
 
The retina, optic nerve, and crystalline lens are developed from the ectoderm,
 
the retina and optic nerve being derived from the ectoderm of the anterior
 
primary cerebral vesicle, whilst the crystalline lens is developed from the ectoderm of the side of the head. The accessories of the eye— e.g., the sclera, cornea,
 
choroid, ciliary body, and iris—are all developed in mesoderm, but ectoderm, as
 
will be seen, is also employed in some of these. The vitreous body, though
 
developed to a certain extent from the mesoderm, is principally formed from the
 
ectoderm.
 
 
 
The earliest indication of the future eye is in the form of a shallow marginal
 
groove on each side in the widely open cerebral plate of embryos with a few
 
somites. As the region grows these grooves become deepened by the upgrowth
 
of the lateral margins, which ultimately fuse in the middle line, in continuity
 
with the fusion of the edges of the medullary folds further back. In this way
 
the open grooves are converted into recesses or lateral pockets of the closed
 
fore-brain, each pocket being in contact from the beginning with the ectoderm
 
of the surface.
 
 
 
The pocket formed in this way is termed the optic recess, and becomes the
 
optic vesicle very soon by its rounded enlargement under the surface ectoderm;
 
such enlargement is mainly at its distal part, its connection with the brain
 
 
 
 
 
THE EYE 1665
 
 
 
being slightly constricted, forming a ' neck ' for the vesicle. As the development
 
goes on this neck is drawn out into a definite stalk, which connects the vesicle
 
with the fore-brain. Stages in these changes can be seen in Fig. 1025. The
 
vesicle is hollow, its cavity being carried into the stalk, and, through this, communicating with that of the fore-brain, which will be the third ventricle. The
 
 
 
 
 
Lens Pit
 
 
 
 
 
Ectoderm
 
 
 
srjer
 
 
 
Optic Stalk
 
 
 
 
 
Optic Vesicle
 
 
 
prifT&yKS-'Ka.
 
 
 
ilM /
 
 
 
 
 
Lens
 
 
 
Cavity of Vesicle
 
a?- m
 
 
 
6i ; w'sn'j.;!'' . ..£31 «
 
 
 
 
 
Optic Stalk
 
 
 
 
 
Pigmentary
 
Layer of I
 
Optic Cup Retinal Layer
 
of Optic Cup
 
 
 
 
 
Fig. 1023.—Development of Crystalline Lens and Optic Vesicle
 
 
 
(Scheme).
 
 
 
The lens is lying in the optic cup.
 
 
 
 
 
enlargement formed by the optic vesicle lies deep to, and in contact with, the
 
ectoderm of the lateral surface of the head (Fig. 1025).
 
 
 
The ectoderm in relation with the optic vesicle becomes thickened and
 
depressed, this depressed portion constituting the lens area. The depressed
 
ectoderm is deepened and converted into a kind of cup, and, the mouth of the
 
fossa becoming constricted, its lips unite. In this manner the lens area becomes
 
transformed into a closed ectodermic sac, called the lens vesicle, from which the
 
 
 
 
 
 
 
Fig. 1024.—Diagram showing (see Text) the Conversion of Optic
 
 
 
Vesicle into Optic Cup.
 
 
 
crystalline lens is differentiated. The lens vesicle now becomes completely
 
separated from the surface ectoderm, with which it was originally continuous
 
 
 
^ Fl The outer wall of the vesicle, facing the rudiment of the lens, is invaginated
 
so as to obliterate the cavity of the vesicle, which is now converted into the
 
oi>tic cut> Fig 1024 gives diagrammatic sections which may help in the comprehension of this change. The middle vertical row of figures here shows sections
 
 
 
105
 
 
 
 
 
 
 
1666
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
along the length of the optic outgrowth; the simple optic vesicle is seen at the
 
top, the commencing invagination of its lower lateral wall is seen next, while
 
the completed invagination is shown in the lowest section. It can be seen that the
 
invagination extends into the optic stalk also. On the left side the invagination
 
is shown by transverse sections of the vesicle, corresponding more or less with
 
the stages of the middle column. Observe that the cavity (V) of the optic
 
 
 
 
 
 
 
 
 
Fig. 1025.—Different Stages in the Development of the Eye
 
(from Reconstruction Models at St. Mary’s Hospital).
 
 
 
A piece of the wall of the optic vesicle has been removed in the first specimen,
 
showing the cavity of the vesicle ; the lens thickening of the ectoderm is
 
beginning to be depressed. In the second the optic outgrowth is entire,
 
and the lens depression is projecting into the cavity of the optic cup. In the
 
third figure removal of part of the wall has opened the cavity of the vesicle,and also the cavity of the cup, in which the lens vesicle is lying, still attached
 
to the ectoderm, its cavity opened by the section. The figures also show
 
the formation of the stalk of the vesicle and the extension into it of the cleft
 
continuous with the cavity of the optic cup.
 
 
 
vesicle is being obliterated, replaced by the cavity (C) of the optic cup, which is
 
still open in front and below; the last section in the middle column has gone
 
along this interval between the two sides of the cup. The interval is termed
 
the choroidal or foetal fissure, and extends into the stalk. It closes later by the
 
apposition and rapid fusion of its lips, so completing the optic cup. The righthand column of sections is made from the distal end towards the brain; they show
 
the concavity in the vesicle, and in the stalk, lost in the last section.
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EYE
 
 
 
 
 
1667
 
 
 
The lens vesicle, when it separates from the surface ectoderm, lies in the
 
opening of the optic cup. Vascular mesoderm extends into the cavity of the
 
cup through the choroidal fissure, behind and below the lens vesicle; when the
 
fissure closes, the mesoderm within the cavity of the cup loses its connection
 
with the outer mesoderm, except at the end of the fissure, where a relatively
 
large vessel persists, and becomes ultimately the central artery of the retina.
 
Since the end of the fissure is in the optic stalk, which becomes the optic nerve,
 
this artery passes in the terminal piece of the nerve to enter the eye. The artery,
 
when first formed, is known as the hyaloid artery, and is distributed over the
 
posterior surface of the lens.
 
 
 
In cases of non-closure of the choroidal fissure the region of the fissure
 
remains unpigmented, and one of two congenital deficiencies in the eye is met
 
with, each being known by the general term coloboma. If the patent fissure
 
affects the ventral wall of the optic cup, then the deficiency in pigment affects
 
the choroid, and the condition is known as coloboma choroidea. If the patent
 
fissure affects the lower margin of the optic cup, then the deficiency affects the
 
lower part of the iris, and the condition is known as coloboma iridis.
 
 
 
As stated, the wall of the optic cup consists of two layers. The outer layer,
 
which is comparatively simple, gives rise to the pigmentary layer of the retina.
 
The inner layer is, on the other hand, very complicated. After much differentiation it gives rise to all the other layers of the retina. The mesodermic tissue,
 
which invests the optic cup, gives rise to the sclera, cornea, choroid, ciliary
 
body (including the ciliary processes and ciliary muscle), and iris. The ciliary
 
processes are covered by layers from the (ectodermal) walls of the cup.
 
 
 
Crystalline Lens. —The lens is of ectodermic origin. The surface ectoderm
 
on the lateral aspect of the head opposite the optic vesicle becomes thickened
 
and depressed to form, as stated, the lens area. The depressed ectoderm is
 
deepened and converted into a kind of cup. The mouth of the cup becomes
 
constricted, and its lips unite. In this manner the lens area becomes transformed into a closed ectodermic sac, called the lens vesicle, from which the
 
crystalline lens is differentiated. The lens vesicle becomes completely separated
 
from the surface ectoderm, with which it was originally continuous. It is now
 
received into the optic cup, which has been formed in connection with the optic
 
vesicle, its position being just within the mouth of the cup, the circumference
 
of the margin projecting slightly in advance of the vesicle.
 
 
 
The anterior and posterior walls of the lens vesicle at this stage consist of
 
several layers of cylindrical cells, and the vesicle contains a small central cavity.
 
The anterior wall becomes gradually thin, and is ultimately formed of one layer
 
of flattened cells, these cells constituting the anterior epithelium of the adult
 
crystalline lens. The cells of the posterior wall become elongated in a forward
 
direction, obliterating the cavity of the vesicle, and coming into contact with
 
the anterior wall. By this process of cell elongation the lens-fibres are formed.
 
At the equator of the lens the cells of the anterior and posterior walls merge
 
gradually into one another through the medium of a transitional zone of columnar
 
cells.
 
 
 
At this stage in its development the crystalline lens consists of (1) an anterior
 
epithelial wall, and (2) a posterior wall composed of elongated cells forming
 
the lens-fibres.
 
 
 
As development proceeds, additional lens-fibres are formed by the proliferation of cells at the equator of the lens. These fibres are laid down in successive
 
layers, which are arranged concentrically.
 
 
 
Capsule of the Crystalline Lens.— At an early period in its development the
 
lens becomes invested by a mesodermic capsule, freely supplied with bloodvessels derived from the hyaloid artery and anterior ciliary arteries. This
 
capsule is known as the tunica vasculosa. It persists throughout the period of
 
active growth of the lens, and then undergoes retrogression to form the permanent lens capsule. The portion of the tunica vasculosa which covers the
 
front part of the lens is called the membrana papillaris, but this usually disappears
 
prior to birth. It may, however, be present at birth, giving rise to the condition
 
 
 
 
 
i668
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
known as atresia pupillce. Towards the end of intra-uterine life the tunica
 
vasculosa undergoes retrogression and becomes transformed, as stated, into the
 
permanent lens capsule, which is a transparent, homogeneous, elastic membrane.
 
 
 
This mesodermal pupillary membrane is a continuation across the open
 
mouth of the cup of the plane of the choroidal layer. It is, therefore, on the
 
outer surface of the developing iris, of which it forms the mesodermal base, the
 
muscles being derived from the actual ectodermal or retinal layer itself.
 
 
 
Development of the Optic Cup and Optic Stalk. —The optic cup, as stated, is
 
formed by the invagination of the distal or outer wall of the optic vesicle, the
 
invagination also affecting the ventral wall of the optic vesicle and the ventral
 
wall of the part of the optic stalk which is adjacent to the optic vesicle, thereby
 
giving rise to the choroidal fissure. The mouth of the optic cup is directed
 
towards the lateral aspect of the head, and the lens vesicle lies just within the
 
mouth. That the invagination of the optic cup is not caused by the growth
 
of the lens vesicle has been proved by experimental transplantations on amphibian
 
embryos. The margin of the cup projects slightly over the lens vesicle, and the
 
circumference of this margin represents the outline of the pupil. The wall of the
 
cup consists of two layers —namely, inner and outer, the inner representing the
 
distal or outer wall of the optic vesicle, which has now become invaginated, or
 
folded inwards. The cup is divisible into two regions—namely, (i) the ciliary
 
region, adjoining the margin of the cup; and (2) the fundus. The line of separation between these two regions corresponds to the ora serrata of the adult eye.
 
 
 
The ciliary region of the optic cup is associated with the ciliary body (including the ciliary processes and ciliary muscle) and the iris, which are developed
 
from the thickened anterior part of the choroid. The outer layer of the ciliary
 
portion, as elsewhere, forms the pigmentary layer of the retina. The inner
 
layer of the ciliary portion, which is very thin, forms (1) the pars ciliaris retinae
 
on the posterior surfaces of the ciliary processes, and (2) the pigmented pars
 
iridica retinae [uvea) on the posterior surface of the iris.
 
 
 
The fundus of the optic cup is the proper retinal region. The outer layer
 
forms, as in the ciliary region, the pigmentary layer of the retina. The inner
 
or retinal layer becomes differentiated into all the layers of the retina except the
 
pigmentary layer. The changes which it undergoes are very complicated.
 
Its thickness is considerably increased, and it subdivides into two layers—
 
outer and inner—from which the various retinal strata (except the outer pigmentary layer) are specialized.
 
 
 
The optic stalk is transformed into the optic nerve. The stalk is at first
 
hollow, its cavity communicating with that of the optic vesicle on the one hand,
 
and with the third ventricle of the brain on the other. As stated, the choroidal
 
fissure involves the under surface of the optic stalk near the optic vesicle, as
 
well as the under surface of the optic vesicle itself. When the choroidal fissure
 
undergoes closure, the hyaloid artery, which passed through that fissure, becomes
 
enclosed within the optic stalk, and forms the arteria centralis retincc of adult
 
life. By the closure of the choroidal fissure, and the consequent enclosure of
 
the hyaloid artery, the cavity of the distal portion of the optic stalk becomes
 
obliterated. Inasmuch as the ventral or lower wall of this part of the stalk
 
has been previously invaginated, the wall of the stalk is now composed of two
 
layers—outer and inner—the inner being formed by the invaginated ventral
 
or lower wall. The outer layer of the optic stalk is now continuous with the
 
outer layer of the optic cup, whilst the inner layer of the optic stalk is continuous
 
with the inner layer of the optic cup. As regards the proximal part of the optic
 
stalk, its cavity becomes gradually closed. The wall of the optic stalk becomes
 
thickened, its cells proliferate, and they give rise to the neuroglial or sustentacular
 
tissue of the future nerve. The nerve-fibres which build up the optic nerve are
 
regarded as having two sources. The majority of them represent the axons of
 
the ganglion cells of the retina, which pass in the optic stalk to the diencephalon
 
and mesencephalon. These are therefore centripetal fibres. Other fibres are
 
regarded as being centrifugal, these arising in connection with the diencephalon
 
and mesencephalon.
 
 
 
 
 
THE EYE
 
 
 
 
 
1669
 
 
 
 
 
Vitreous Body. —This body is formed within the optic cup, for the most part
 
posterior to the lens vesicle. It is principally developed from the ectoderm, but
 
the mesoderm also takes part in its formation. The ectodermic fibres are derived
 
from those cells which pertain to the sustentacular fibres of the retina.
 
 
 
These ectodermal fibres form a very delicate reticulum (Fig. 1026) connecting
 
the lens vesicle and the inner layer of the optic cup. Mesodermal ingrowth
 
through the choroidal fissure brings in vessels which ramify to some extent
 
between the ectodermal connecting strands, but for the most part pass forward
 
to the back of the growing lens, over which the vessels spread, with their thin
 
mesodermal surrounding. The main vessel thus reaching the lens is the hyaloid
 
artery, and this with its surrounding fine mesoderm occupies at first a large part
 
of the small cavity of the cup, enclosed by ectodermal processes, more or less
 
avascular in the more peripheral parts of the cup. This is the state known as
 
the primary vitreous, characterized by
 
ectodermal formations connected in
 
origin with both retina and lens, and
 
associated fairly intimately with vascular mesoderm. The central hyaloid
 
artery is distributed over the back of
 
the lens, its terminal branches meeting, at the periphery of this structure,
 
vessels which enter the cup from the
 
outside, turning round its rim.
 
 
 
The primary vitreous is gradually
 
succeeded and replaced by the secondary vitreous. The time of the beginning of the change is usually considered to be about the fifth to sixth
 
week, when the posterior hyaloid
 
capsule of the lens makes its appearance; after this the slowly increasing
 
ectodermal element can be produced
 
only by the retina. It is this element
 
which, by its growth, occupies the extra
 
space resulting from the increasing size
 
of the eyeball, so that it gradually
 
comes about that the original vascu- C, wall of fore-brain ; OP.V., points to
 
lar mesodermo-ectodermal formation cavity of optic vesicle; OC, to cavity
 
 
 
 
 
 
 
Fig. 1026.—Vertical Section through
 
Eye in 5 Mm. Embryo.
 
 
 
 
 
of optic cup; L.P., lens pit; ECT., surface ectoderm. Protoplasmic processes
 
connect the lens pit with the inner
 
wall of the cup.
 
 
 
 
 
(primary vitreous) is surrounded and
 
enclosed by an increasing mass of ectodermal secondary vitreous ; this is
 
largely non-vascular, but does not
 
become completely avascular until the
 
hyaloid artery atrophies. The vessels are contained in a central funnel-shaped
 
‘ space ’ in this stage, surrounded by the secondary vitreous, which does not
 
compress them in any way; the broad end of the funnel is behind the lens, over
 
which the vessels extend as before, making a vascular capsule for the structure,
 
and joining round the periphery with vessels reaching its anterior surface. The
 
anterior part of this tunica vasculosa has been seen already to form the pupillary
 
 
 
m The bloodvessels atrophy and disappear in the latter part of foetal life, when the
 
interval in which they lay persists as the hyaloid (or vitreous) canal, or canal
 
of Cloquet, the remaining ectodermal substance, now avascular, being the
 
 
 
definite vitreous. r , r J ,
 
 
 
About the end of the third month the growth forward of the nm of the optic
 
 
 
cup (to form the ectodermal portion of the iris) is accompanied by the appearance
 
of a more fibrillar vitreous formation corresponding with it; this is sometimes
 
referred to as the tertiary vitreous, and the fibrils of the suspensory ligament of
 
the lens are developed in this formation.
 
 
 
 
 
1670
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
That part of the hyaloid artery which lies in the fissure in the optic stalk
 
remains as the extra-ocular part of the arteria retinae centralis. The actual
 
arteries of the retina are secondary and late branches which extend into that
 
layer from the hyaloid artery as this enters the eyeball; when the lentine part of
 
the vessel atrophies, these retinal branches remain and enlarge.
 
 
 
Derivatives of the Mesodermic Envelope of the Optic Cup. —These are as
 
follows: (1) Sclera, (2) cornea, (3) choroid, (4) ciliary body (including the ciliary
 
processes and ciliary muscle), and (5) iris.
 
 
 
The mesoderm which invests the outer surface of the optic cup is disposed in
 
two layers —outer and inner. The outer layer has a fibrous character, and gives
 
rise to the sclera, of which the cornea is a forward extension. The inner layer
 
is vascular, and gives rise to the choroid, and mesodermal bases of the ciliary
 
body and iris. The outer dense fibrous layer of the mesoderm of the outer
 
surface of the optic cup, as stated, gives rise to the sclera. From its anterior
 
margin a thick lamina of mesoderm is prolonged between the lens vesicle and the
 
surface ectoderm. This lamina shows two layers—superficial and deep. The
 
superficial layer becomes differentiated into the cornea, which is thus genetically
 
continuous with the sclera. The deep layer becomes the pupillary membrane
 
(see above). Between these two layers there is an interval, which represents the
 
aqueous chamber.
 
 
 
The inner vascular layer of the mesoderm of the outer surface of the optic
 
cup, as stated, gives rise to the choroid. The anterior margin of the choroid,
 
which adjoins the margin of the optic cup (ciliary region) becomes thickened,
 
and gives rise to the ciliary body, in connection with which the ciliary processes
 
and ciliary muscle are developed. The ciliary processes become covered posteriorly
 
by the pars ciliaris retince, which is a thin retinal expansion from the ciliary
 
region of the optic cup. The iris is also developed at the anterior margin of the
 
choroid in the form of a ring of mesoderm. In this mesoderm the fibres forming
 
the dilator pupillce and sphincter pupillce muscles are formed by proliferation
 
of the ectodermal cells of the edge of the optic cup, which has extended forward
 
in front of the lens, and the back of the iris receives a pigmentary covering {uvea)
 
from the pars iridica retince.
 
 
 
 
 
/
 
 
 
 
 
CHAPTER XVII
 
 
 
THE EAR
 
 
 
 
 
The organ of hearing is divided into three parts—the external,
 
middle, and internal ear.
 
 
 
 
 
External Ear.
 
 
 
The external ear consists of the auricle (or pinna) and the external
 
auditory meatus. The former has been already described (see p. 1294)*
 
The external auditory meatus extends from the bottom of the
 
concha to the membrana tympani, and is about 1 inch in length.
 
It consists of two parts—outer, or cartilaginous, and inner, or osseous.
 
The cartilaginous part, which is also fibrous, is about J inch in length,
 
and the osseous part, which lies within the petrous portion of the
 
temporal bone, is about § inch long. The widest part of the meatus
 
is its orifice, which is oval, the long measurement being vertica .
 
The narrowest part is situated in its osseous portion, about T mch
 
from the tympanic membrane, and it is known as the isthmus. There
 
is another constriction of the canal situated near the deep end of t e
 
cartilaginous part, and produced by a projection which is placed
 
antero-inferiorly. The chief direction of the canal is inwards and
 
slightly forwards. At first it is also inclined upwards, then backwards,
 
 
 
and finally downwards. . ,
 
 
 
The cartilaginous part is continuous with the cartilage of the auricle,
 
and is attached to the external auditory process of the temporal bone.
 
Its cartilage is folded so as to form a deep groove which is open at its
 
upper and back part, the cartilaginous deficiency being completed
 
by fibrous tissue. In the anterior wall of the cartilaginous part are
 
two clefts (called the fissures of Santorini ) which are occupied by fibrous
 
Ssuf In important and close inferior relation of the cartilaginous
 
 
 
meatus is the parotid gland (see Fig. 1027). ,
 
 
 
The osseous part has been described in connection with the temporal
 
hone (d IQ4) At its deep end there is a narrow groove, called the
 
sulcus tvmianicus, which forms about five-sixths of a circle, the
 
 
 
deficiency being placed superiorly, at the V^femporaf^The
 
rinp- ic completed by the squamous part of the temporal bone, me
 
 
 
tympanic membrane is set obliquely within the tympanic sulcus
 
being inclined in such a way that its front part is nearer the nudd
 
line of the body than its back, and its lower part nearer the middle
 
line than the upper. The floor and anterior wall of the meatus
 
consequently longer than the roof and posterior wall.
 
 
 
^ 1671
 
 
 
 
 
 
 
1672
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
The meatus is lined with skin, which is continuous with that of
 
the auricle. In the osseous part of the canal the skin is very thin,
 
and is provided with vascular papillae, but is destitute of glands and
 
hairs.. It is reflected over the outer surface of the membrana tympani,
 
of which it forms the outer layer. In the cartilaginous part of the canal
 
the skin is thicker, and is provided with hairs, connected with the
 
follicles of which are sebaceous glands. In addition to these there are
 
convoluted tubular glands, similar in structure to sweat-glands, and
 
called the ceruminous glands, which secrete the ear-wax.
 
 
 
Blood-supply.—The arteries are derived from the posterior auricular
 
of the external carotid, the deep auricular of the first part of the maxil
 
 
 
Upper Part ofHelix
 
 
 
 
 
Lateral Ligament of the Malleus
 
 
 
1
 
 
 
Incus
 
 
 
 
 
Semicircular Canals
 
 
 
 
 
Concha
 
 
 
 
 
External Auditory
 
Meatus
 
 
 
 
 
 
 
Malleus
 
Vestibule
 
__ Cochlea
 
x , Tympanum
 
 
 
Tensor Tympani Muscle
 
 
 
Apex of Pet. Portion
 
of Temporal Bone
 
 
 
_Anterior Lig. of
 
 
 
the Malleus
 
 
 
-Internal Carotid
 
 
 
Artery
 
 
 
 
 
Lobule
 
 
 
Pharyngotympanic Tube
 
 
 
 
 
Parotid Gland
 
 
 
 
 
Tip of Styloid Process of
 
Temporal Bone
 
 
 
 
 
Tympanic Membrane
 
 
 
Iug. 1027. General View of the Right Organ of Hearing (after
 
 
 
Hirschfeld and Leveill£).
 
 
 
The external ear and middle ear are seen in section.
 
 
 
 
 
iary, and the anterior auricular branches of the superficial temporal.
 
The veins follow the course of the arteries.
 
 
 
Lymphatics. These pass to the mastoid glands and to the preauricular lymphatic glands.
 
 
 
Nerves. The auriculo-temporal nerve gives two branches to the
 
meatus, upper and lower, which enter it by passing between the
 
cartilaginous and osseous walls. The upper branch supplies the skin
 
covering the upper part of the membrana tympani, while the auricular
 
branch (Arnold s nerve) of the vagus supplies that of the osseous
 
part of the canal in its lower and back part, and also that covering
 
the lower part of the membrana tympani.
 
 
 
Early Condition of the Meatus.—At birth the osseous part of the
 
 
 
canal is represented by the tympanic annulus and a small portion of
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EAR
 
 
 
 
 
1673
 
 
 
the squamous part of the temporal bone. It is connected by fibrous
 
tissue to the cartilaginous framework of the auricle, and within this
 
fibrous tissue the osseous canal is formed by two outgrowths from the
 
tympanic annulus.
 
 
 
 
 
Middle Ear.
 
 
 
I he middle ear, or tympanum, is an irregular space within the
 
petrous part of the temporal bone, which lies between the membrana
 
tympani externally and the outer osseous wall of the internal ear or
 
labyrinth internally. It is lined with mucous membrane, and it
 
communicates with the naso-pharynx by means of the pharyngotympanic tube, through which it receives air. It has three parts:
 
(1) the tympanum proper, or cavum tympani; (2) the attic, or epitympanic recess; and (3) the tympanic or mastoid antrum.
 
 
 
The tympanum proper (or cavum tympani) is situated between the
 
tympanic membrane and the outer wall of the internal ear. Its
 
contents are as follows:
 
 
 
1. A chain of ossicles (malleus,
 
 
 
incus, and stapes), with
 
their ligaments.
 
 
 
2. Muscles.
 
 
 
The vertical and antero-posterior diameters (inclusive of the attic)
 
are fully \ inch. The transverse measurement is from | to £ inch,
 
except opposite the centre of the membrana tympani, where it is
 
only T V inch, and the shape of its cavity may, perhaps, be visualized
 
by likening a cast of it to a biconcave disc about the size of a threepenny piece.
 
 
 
The tympanic cavity has six walls—lateral, medial, roof, floor,
 
anterior, and posterior.
 
 
 
The lateral wall is formed chiefly by the tympanic membrane,
 
which has the handle of the malleus fixed to it, and slightly by the
 
tympanic annulus, within the circumference of which there is a groove,
 
called the tympanic sulcus, in which the membrane is set. The tympanic annulus and sulcus are interrupted superiorly by a notch, called
 
the tympanic notch. In front of the tympanic annulus is the open,
 
inner extremity of the squamo-tympanic fissure, which lodges the
 
processus gracilis of the malleus, and transmits the tympanic branch
 
of the internal maxillary artery. At the inner end of the fissure is
 
the opening of the iter chordce anterius, by which the chorda tympani
 
nerve leaves the tympanum.
 
 
 
The (medial) wall (see Fig. 1028) separates the tympanum from the
 
internal ear or labyrinth. It is very irregular, and is formed by the
 
following parts :
 
 
 
1 The fenestra vestibuli. 3 - The promontory.
 
 
 
2. Projection of the facial canal. 4 - The fenestra cochleae.
 
 
 
5. The sinus tympani.
 
 
 
 
 
3. Nerves.
 
 
 
4. Bloodvessels.
 
 
 
5. Air.
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
^74
 
 
 
 
 
The fenestra vestibuli is situated in a depression, called the fossa
 
ovalis, at the upper part of the inner wall, and it leads into the cavity
 
of the vestibule. It is irregularly oval, and is elongated from before
 
backwards. It is occupied by the foot-piece of the stapes, and the
 
annular ligament which connects the circumference of the foot-piece
 
to the margin of the opening, the margin being covered by cartilage.
 
 
 
The projection of the facial canal lies above the fenestra ovalis.
 
The canal, which contains the facial nerve, is here directed backwards,
 
and has walls of a paper-like thinness.
 
 
 
The promontory is seen below the fossa ovalis, between it and the
 
fossa rotunda, and slightly in front of both. It is a rounded promin
 
 
 
Mastoid
 
 
 
Antrum
 
 
 
 
 
 
 
Sinus Tympam Outlet of Facial Canal at
 
Stylo-mastoid Foramen
 
 
 
kiG. 1028. Section through the Petrous and Mastoid Portions of the
 
Temporal Bone, showing the Tympanum and Mastoid Cells.
 
 
 
ence made by the first turn of the cochlea, and is grooved by the nerves
 
of the tympanic plexus.
 
 
 
The fenestra cochlese is situated in a funnel-shaped depression
 
called the fossa rotunda, below and behind the promontory. It leads
 
into the scala tympani of the cochlea, and in the recent state is closed
 
by the secondary membrane of the tympanum.
 
 
 
1 he sinus tympani is a depression behind the promontory, and
 
between the fossa ovalis and fossa rotunda. In close relation to this
 
is the ampulla of the posterior semicircular canal.
 
 
 
The roof of the tympanum is a thin plate of bone, called the tegmen
 
tympani, which forms part of the anterior surface of the petrous part
 
of the temporal bone.
 
 
 
The floor, narrower than the roof, is a thin plate of bone which
 
separates the tympanum from the jugular fossa.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EAR
 
 
 
 
 
1675
 
 
 
 
 
The anterior wall is narrow, owing to the descent of the roof, and
 
the inclination towards each other of the outer and inner walls. In
 
it are the openings of two canals, the upper of which lodges the tensor
 
tympani muscle, whilst the lower is the osseous part of the pharyngotympanic tube. The two orifices are separated by the margin of the
 
processus cochleariformis. The carotid canal lies just in front of the
 
lower part of the anterior wall.
 
 
 
 
 
 
 
Fig. 1029.—Diagrammatic Outline of Tympanum and Associated
 
 
 
Recesses.
 
 
 
 
 
The posterior wall is formed by the anterior or tympanic surface
 
of the petrous part of the temporal bone. From above downwards
 
the following parts are seen: (1) the opening of the mastoid antrum,
 
which communicates with the attic of the tympanum, or epitympanic
 
recess; (2) a depression called the fossa incudis, receiving the short
 
process of the incus* (3) a small conical projection, called the pyramid,
 
at the summit of which is an opening for the tendon of the stapedius
 
muscle (posteriorly the canal within the pyramid, which contains the
 
 
 
 
 
 
 
Mastoid Antrum
 
 
 
 
 
Lateral Semicirc.C. ~ *
 
Pyramid •
 
Sinus Tympanum —
 
 
 
 
 
-Epitympanic Recess
 
 
 
-Site of Geniculate Ganglion
 
 
 
Fenestra Vestibuli
 
 
 
Promontory
 
 
 
Fenestra Cochleae
 
 
 
 
 
Fir jo^o_ Diagram to show Course and Relations of Facial Canal on
 
 
 
' 'the Medial and Posterior Walls of the Tympanum.
 
 
 
 
 
stapedius muscle, passes downwards in the posterior wall of the
 
tympanum, and communicates with the descending part of the canal
 
which contains the facial nerve; this explains how the branch of that
 
nerve to the stapedius reaches the muscle); and (4) the iter chordae
 
 
 
posterius, for the chorda tympani nerve. .
 
 
 
Tympanic Membrane.-This is the membrane which closes the
 
inner extremity of the external auditory meatus. It is situated on
 
the outer wall of the tympanum, of which it forms the chief part, and
 
it is set for the most part in the sulcus tympamcus, which marks the
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1676
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
inner surface of the tympanic annulus. Superiorly, however, where
 
the ring is wanting, the membrane is attached to the tympanic notch
 
(of Rivinus). This part of it is thinner and looser than the rest, and
 
is called the membrana flaccida, or Shrapnell’s membrane. The
 
attachment of the membrana tympani to the sulcus is by a thickened
 
ring of fibres, called the annulus fibrosus. This annulus passes from
 
the extremities of the notch to the short process of the malleus in the
 
form of two bands, the anterior and lateral ligaments of the malleus,
 
which form the lower boundary of the membrana flaccida. The membrane is set obliquely in the tympanic sulcus, so that its lower part
 
forms an acute angle with the floor of the meatus externus, and its
 
upper part an obtuse angle with the roof of the passage.
 
 
 
 
 
Superior Ligament of Malleus
 
 
 
 
 
Head of Malleus
 
Insertion of Tensor Tympani
 
 
 
Chorda Tympani Nerve
 
 
 
 
 
Pharyngo-tympanic
 
Tube
 
 
 
 
 
 
 
Superior Ligament of Incus
 
Body of Incus
 
 
 
Attic of Tympanum
 
 
 
^ Short Process of
 
Incus
 
 
 
L ’\ST ^Posterior Liga^ ment of Incus
 
 
 
s ^_Long Process of
 
 
 
 
 
_Processus Orbicu
 
1 & • laris of Incus
 
 
 
y ' 0 _Handle of Malleus
 
 
 
 
 
 
_Membrana Tympani
 
 
 
 
 
 
 
 
 
Fig. 1031.—The Right Membrana Tympani, Malleus, and Incus
 
(Internal, Posterior, and Superior View) (Spalteholz).
 
 
 
 
 
The tympanic membrane is somewhat oval. In the vertical
 
direction it measures about 10 mm., and horizontally from 8 to 9 mm.
 
The handle of the malleus lies between the mucous and fibrous layers
 
of the membrane, and descends to a point a little below its centre,
 
where it ends in a small knob, from which the radiating fibres of the
 
membrane proceed. This knob is firmly attached, and, being directed
 
inwards, the membrane is consequently drawn inwards at that point,
 
and its outer surface presents a slight conical depression, the deepest
 
part of which is called the umbo.
 
 
 
Structure.— The membrane consists of three layers—external,
 
middle, and internal.
 
 
 
The external or cutaneous layer is very thin, and is derived from
 
the skin of the external meatus. It contains no glands, is freely provided with bloodvessels and nerves, and is covered by stratified
 
squamous epithelium.
 
 
 
 
 
/
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EAR
 
 
 
 
 
1677
 
 
 
The middle or fibrous layer forms the proper substance of the
 
membrane, and consists of fibrous tissue. The fibres are radial and
 
circular. The radial fibres lie beneath the cutaneous layer, and radiate
 
from the handle of the malleus to the annulus fibrosus. The circular
 
fibres are deep to the radial fibres, and are most numerous towards the
 
circumference of the membrane. Both sets of fibres are absent from
 
the membrana flaccida.
 
 
 
The internal or mucous layer is continuous with the mucous membrane of the tympanum, and is covered by a single layer of squamous
 
epithelium.
 
 
 
The membrana flaccida, pars flaccida, or Shrapnell’s membrane, has
 
cutaneous and mucous layers only. These are united by connective
 
tissue, which is so loosely arranged that the membrane is flaccid. This
 
part is very liable to perforation.
 
 
 
Cone of Light.—Extending from the knob, in which the handle of
 
the malleus terminates, downwards and inwards to the antero-inferior
 
margin of the membrana tympani there is seen a specially bright
 
reflection, triangular in outline, with the apex towards the umbo.
 
This is called the cone of light.
 
 
 
Arterial Supply of the Tympanic Membrane.—(1) Deep auricular
 
branch of the maxillary artery. This vessel, which passes through the
 
anterior wall of the external meatus, supplies the cutaneous layer. It
 
descends from the skin of the roof of the meatus along the course of the
 
handle of the malleus to the umbo, where it divides into branches
 
which radiate towards the circumference of the membrane. (2) The
 
stylo-mastoid branch of the posterior auricular; and (3) the tympanic
 
branch of the maxillary. The former artery enters the tympanum from
 
the facial canal, and the latter through the squamo-tympanic fissure.
 
Branches from them supply the mucous layer, and form an anastomotic
 
ring around the circumference of the membrane. The fibrous layer
 
receives its arterial supply from the vessels of the cutaneous and
 
mucous layers.
 
 
 
The veins join the external and internal jugular.
 
 
 
Nerve-supply.—(1) The auriculo-temporal of the mandibular, (2) the
 
auricular branch of the vagus, and (3) branches from the tympanic
 
plexus.
 
 
 
Secondary Membrane of the Tympanum.—This membrane closes
 
the fenestra cochleae on the inner wall of the tympanum, and separates
 
the tympanic cavity from the scala tympani of the cochlea. It is
 
concave towards the tympanum, and, like the membrana tympani,
 
consists of three layers. The external layer is formed by the tympanic
 
mucous membrane; the middle layer is fibrous; and the internal layer is
 
formed by the lining membrane of the cochlea.
 
 
 
The mastoid antrum and mastoid air-cells are described with the
 
temporal bone on p. 188, while the Eustachian or pharyngo-tympanic
 
tube is dealt with on p. 1378.
 
 
 
 
 
1678
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Lateral Process
 
Long Process
 
 
 
 
 
 
 
Ant.
 
 
 
Process
 
 
 
 
 
Plandie
 
 
 
 
 
Fig. 1032.—The Malleus.
 
 
 
1. anterior view; 2, posterior view.
 
 
 
 
 
Ossicles of the Tympanum.
 
 
 
The tympanum contains three small bones, arranged in the form
 
of a chain which extends from the membrana tympani to the fenestra
 
vestibuli. The bones are the malleus, the incus, and the stapes. The
 
malleus is related to the membrana tympani, the stapes to the fenestra,
 
and the incus occupies an intermediate position between these two.
 
 
 
The malleus is so named from its resemblance to a hammer. It is
 
composed of a head, neck, handle, and two processes, long and short.
 
 
 
T 2 The head is the upper, enlarged,
 
 
 
Facet for incus rounded end. Posteriorly it has
 
 
 
a saddle-shaped facet, directed
 
obliquely downwards and inwards,
 
for articulation with the incus in a
 
synovial joint. The neck is the
 
constricted part below the head.
 
The handle (; manubrium) is directed
 
downwards, inwards, and backwards
 
from the neck; it is compressed
 
from before backwards, slightly
 
curved, and ends in a knob. It
 
lies between the fibrous and mucous layers of the membrana tympani,
 
descending to a point a little below the centre of the membrane. It
 
is firmly attached to the fibrous layer by its periosteum. The tensor
 
tympani muscle is inserted into the inner part close to its root. The
 
long or anterior process (processus gracilis ), which is slender, springs
 
from the front of the neck, and is directed forwards and downwards to
 
the petro-tympanic fissure, where it is embedded in fibres which form
 
part of the anterior ligament of the malleus, and connect it to the
 
margins of the fissure. The long process is in the adult for the most
 
part replaced by fibrous tissue except close to the neck of the malleus.
 
In early life it is continuous with Meckel’s cartilage. The short or
 
lateral process is situated immediately below the long process. It is
 
directed laterally to the upper part of the
 
membrana tympani, with which it is connected by the annulus fibrosus. It is also
 
connected with the extremities of the notch
 
by the anterior and posterior malleolar
 
ligaments.
 
 
 
Ihe incus resembles an anvil. It consists
 
of a body and two processes—short and
 
 
 
long. The body is thick, somewhat four- ^ ~ Head ° f Sta fu
 
 
 
sided, and laterally compressed. Anteriorly y^ 08 '
 
 
 
it presents a saddle-shaped articular surface
 
 
 
for the head of the malleus, with which it forms a synovial joint.
 
The short process is directed backwards, is tipped with cartilage, and
 
articulates with the fossa incudis on the posterior wall of the tympanum. The long process is directed downwards and medially, behind
 
 
 
 
 
Facet
 
 
 
for Malleus
 
 
 
/ Short Process
 
 
 
/
 
 
 
 
 
 
 
Long Process
 
 
 
 
 
'*■' Lentiform Nodule for
 
Head of Stapes
 
 
 
 
 
THE EAR
 
 
 
 
 
1679
 
 
 
 
 
and parallel to the handle of the malleus. Its lower extremity is bent
 
inwards, and becomes narrowed into a neck, upon which is placed a
 
disc-like knob of bone, called the os orbiculare, which is covered by
 
cartilage for articulation with the head of the stapes. In early life,
 
and up to the sixth month of intra-uterine life, this process forms a
 
separate ossicle.
 
 
 
The stapes resembles a stirrup. It has a head, neck, two crura,
 
and a foot-piece or base. The head is directed laterally, is concave
 
and covered by cartilage, and articulates with the processus lenticularis
 
of the incus. The neck is the constricted part which lies immediately
 
internal to the head. Posteriorly it gives
 
insertion to the stapedius muscle. The
 
crura are anterior and posterior respectively,
 
and spring from the neck. They diverge as
 
they pass inwards, and are attached to the
 
foot-piece near its extremities. The anterior
 
crus is straighter and shorter than the
 
 
 
posterior. The foot-piece or base is some- Malleus
 
what oval, is directed medially, and occupies incus,,
 
the fenestra ovalis, which it almost completely fills; its circumference is covered by
 
cartilage, being attached to the margins of
 
the fenestra by annular ligamentous fibres. Stapes-
 
The arch formed by the crura and foot-piece _ ~
 
 
 
is occupied by a delicate membrane, which tympanic Os
 
is attached to a slight groove on the inner sicles in Position.
 
aspect of the arch.
 
 
 
Development of the Tympanic Ossicles— The malleus and incus are usually
 
regarded as being developed from the proximal end of Meckel’s cartilage,
 
which forms the cartilaginous bar of the first or mandibular arch. According to
 
some authorities, however, the incus is developed from the hyoid bar. The stapes
 
is developed from the dorsal part of the hyoid bar of the second visceral arch.
 
 
 
Ligaments of the Ossicles.—The synovial joints between the malleus
 
and incus and between the incus and stapes are provided with thin
 
capsular ligaments. The ligaments which connect the ossicles to the
 
walls of the tympanic cavity are five in number, three of them belonging
 
to the malleus, one to the incus, and one to the stapes.
 
 
 
The ligaments of the malleus are anterior, lateral, posterior, and
 
superior. The anterior ligament is arranged as a fibrous band which
 
extends from the root of the long process to the petro-tympanic fissure,
 
through which it passes to be attached to the spine of the sphenoid
 
bone. The lateral ligament (or malleolar fold) extends from the
 
short process to the anterior extremity of the tympanic notch. The
 
posterior ligament extends from the short process to the posterior
 
extremity of the notch. The superior ligament extends from the head
 
of the malleus to the roof of the attic or epitympanic recess.
 
 
 
The ligament of the incus connects the short process, near its
 
posterior extremity, to the fossa incudis.
 
 
 
 
 
 
 
 
 
i68o
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
The annular ligament of the stapes connects the circumference of
 
the foot-piece, which is covered by cartilage, to the margin of the
 
fenestra vestibuli, which is also covered by cartilage.
 
 
 
Muscles of the tympanum are the tensor tympani and the stapedius.
 
 
 
Tensor Tympani— Origin .—(i) The cartilaginous part of the
 
pharyngo-tympanic tube; (2) the apex of the petrous part of the
 
temporal bone; and (3) the wall of the osseous canal through which
 
the muscle passes.
 
 
 
Insertion, —The medial aspect of the handle of the malleus close to
 
its root.
 
 
 
Nerve-supply.—A branch from the otic ganglion, and through it
 
from the internal pterygoid branch of the mandibular division of the
 
fifth cranial nerve.
 
 
 
The muscle consists of a fleshy belly, about inch long, and a
 
delicate tendon. In passing backwards to the tympanum it lies in a
 
canal, the entrance to which is situated within the petro-squamous
 
angle of the temporal bone. The canal is placed above the osseous
 
part of the tube, from which it is separated by the processus cochlearifor mis. On entering the tympanum the tendon of the muscle bends
 
sharply over the edge of the processus cochleariformis, and then passes
 
laterally to reach its insertion. The tendon forms very nearly a
 
right angle with the fleshly belly.
 
 
 
Action. —To render tense the membrana tympani by drawing
 
inwards the handle of the malleus, and along with it the membrane.
 
 
 
Stapedius Origin. —The wall of the canal within the pyramid, and
 
of the continuation of this canal in front of the descending part of the
 
facial canal.
 
 
 
The tendon emerges from the canal within the pyramid through a
 
small orifice on the apex.
 
 
 
Insertion. —The posterior aspect of the neck of the stapes.
 
 
 
Nerve-supply. —The facial nerve.
 
 
 
Action. To draw the head of the stapes backwards. The result
 
is that the front part of the foot-piece of the stapes is tilted away
 
 
 
from the vestibule, and its back part is pressed inwards towards the
 
vestibule.
 
 
 
Movements of the Ossicles.—The malleus and incus both act as
 
levers of the first kind, the fulcra of which are represented by an axis
 
passing backwards from the slender process of the malleus. When a
 
sound-wave presses the tympanic membrane inward, the handle of the
 
malleus travels inward with it, and the head of the malleus, or short
 
arm of the lever, moves outward. The upper part, or short arm of
 
the incus lever, must move out too, since it is attached to the head
 
of the malleus, and the long process moves inward, thus pressing the
 
 
 
stapes into the fenestra ovalis and compressing the perilymph in the
 
cochlea.
 
 
 
Ihe secondary membrane of the tympanum, stretched across the
 
fenestra rotunda, is bulged outward by the perilymph, thus allowing
 
vibrations to travel through that fluid.
 
 
 
 
 
/
 
 
 
 
 
THE EAR
 
 
 
 
 
1681
 
 
 
Mucous Membrane of the Tympanum.—The tympanic mucous
 
membrane is continuous anteriorly with that of the naso-pharynx
 
through the pharyngo-tympanic (or Eustachian) tube. Posteriorly it is
 
prolonged into the mastoid antrum, and thence into the mastoid cells.
 
It forms the internal layer of the tympanic membrane, and the external
 
layer of the secondary membrane of the tympanum. It also furnishes
 
sheaths for the tendons of the tensor tympani and stepedius muscles,
 
and for the chorda tympani nerve. Two folds extend downwards from
 
the roof of the attic or epitympanic recess, one in front of and the other
 
behind the superior ligament of the malleus. The former is connected
 
with the head of the malleus, and the latter (sometimes described as
 
the superior ligament of the incus) with the incus.
 
 
 
Attic or Epitympanic Recess and its Pouches.—The part of the
 
tympanic cavity which lies above the level of the upper margin of the
 
tympanic membrane is called the attic or epitympanic recess, as distinguished from the atrium or tympanum proper. It contains the
 
head and neck of the malleus, and the body and short process of the
 
incus. These divide it incompletely into two compartments—outer
 
and inner. The outer attic is subdivided into two pouches—superior
 
and inferior. The superior pouch is partially separated from the
 
inner attic by the two mucous folds which have been already referred
 
to as descending from the roof of the attic in front of and behind the
 
superior ligament of the malleus. The inferior pouch of the outer attic
 
is known as the pouch of Prussak. It is bounded laterally by the
 
membrana flaccida, superiorly by the lateral ligament of the malleus,
 
which partially separates it from the superior pouch, and internally
 
by the neck of the malleus. The pouch communicates posteriorly
 
with the tympanic cavity by an opening which is situated a little above
 
the level of the bottom of the pouch. If fluid, therefore, should
 
accumulate in Prussak’s pouch, it may readily lead to perforation of
 
the membrana flaccida.
 
 
 
Two other pouches are present—namely, the anterior and posterior
 
recesses or pouches of Troltsch. These lie one in front of and the other
 
behind the handle of the malleus, and are produced by the fold of
 
mucous membrane which invests the chorda tympani nerve.
 
 
 
The tympanic mucous membrane is covered for the most part by
 
columnar ciliated epithelium, except over the ossicles and membrana
 
tympani, where the epithelium consists of a single layer of squamous,
 
non-ciliated cells.
 
 
 
The tympanic or mastoid antrum is supplementary to the tympanum proper, or cavum tympani, behind which it is situated. It
 
communicates by a large irregular opening with the attic, and is
 
lined with mucous membrane, which is continuous with that of the
 
attic and cavum tympani. Opening from the antrum there are the
 
mastoid cells, which are lined with mucous membrane, continuous
 
with that of the antrum.
 
 
 
The average measurements of the antrum are as follows: vertical,
 
about Q millimetres; antero-posterior, about n millimetres; and
 
 
 
106
 
 
 
 
 
1682
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
transverse, about 8 millimetres. The roof is formed by the thin
 
tegmen tympani, which enters into the formation of the middle fossa
 
of the base of the skull, and is consequently related to the temporal
 
lobe of the cerebrum and its meninges. The genu and descending
 
limb of the sigmoid sinus lie behind the antrum, and a little farther
 
back is the cerebullum. The facial nerve, as it traverses the descending part of its canal, lies in the posterior wall of the cavum tympani,
 
close to the medial wall and in front of the mastoid antrum. This
 
part of the nerve is on a plane anterior to the mastoid process, and is
 
nearly flush with the opening of the antrum. The ampulla of the
 
lateral semicircular canal of the internal ear gives rise to a slight
 
eminence on the medial wall at its anterior part.
 
 
 
The lateral wall corresponds on the surface with the area of the
 
suprameatal triangle of Macewen, and is formed by the postmeatal
 
plate of the squamous portion of the temporal bone. For a description
 
of this triangle, which is the region selected for mastoidectomy , and also
 
for the mastoid cells, see the description of the temporal bone.
 
 
 
Summary of Important Structures closely related to the Mastoid Antrum.
 
 
 
1. Temporal lobe of cerebrum and its meninges (roof).
 
 
 
2. Genu and descending limb of sigmoid sinus, and farther back the cerebellum (posterior wall).
 
 
 
3 - Facial nerve (posterior wall of cavum tympani, close to medial wall and
 
nearly flush with antral opening).
 
 
 
4 - Lateral semicircular canal (anterior part of medial wall).
 
 
 
The upper part of the antrum communicates, as stated, with the
 
attic of the cavum tympani, but the lower part is shut off by bone from
 
the cavity of the cavum tympani.
 
 
 
The mucous membrane of the mastoid antrum is continuous with
 
that which lines the mastoid cells. Anteriorly it is also continuous
 
with the mucous membrane of the attic and cavum tympani or tympanum proper. The mucous membrane of the cavum tympani is
 
continuous anteriorly with that of the pharyngo-tympanic tube, and
 
the mucous membrane of the tube is continuous with that of the
 
naso-pharynx. This extensive and continuous tract of mucous
 
membrane is covered by columnar ciliated epithelium except in the
 
following regions: (1) the promontory; (2) the tympanic ossicles;
 
(3) the tympanic membrane; (4) the mastoid antrum; and (5) the
 
mastoid cells. In these regions the epithelium consists of a single
 
layer of squamous, non-ciliated cells.
 
 
 
It is of considerable importance to note that micro-organisms
 
may pass from the naso-pharynx through the tube into the cavum
 
tympani and attic, and thence into the mastoid antrum and mastoid
 
cells. Purulent affections of these regions may therefore readily be
 
caused in this manner. Such affections may subsequently involve
 
(1) the temporal lobe of the cerebrum and its meninges, (2) the genu
 
and descending limb of the sigmoid sinus, and (3) the internal ear or
 
labyrinth.
 
 
 
 
 
/
 
 
 
 
 
THE EAR
 
 
 
 
 
1683
 
 
 
Arteries of the Tympanum. —The principal arteries are: (1) the tympanic
 
branch of the maxillary, and (2) the stylo-mastoid branch of the posterior
 
auricular. The tympanic artery enters through the petro-tympanic fissure, and
 
supplies the membrana tympani and front part of the tympanum. The stylomastoid artery enters the facial canal through the stylo-mastoid foramen, and
 
passes from the descending part of the canal into the tympanum. It supplies
 
the back part of the cavity and the mastoid cells, and it forms, with the tympanic
 
artery, a ring round the circumference of the membrana tympani.
 
 
 
In addition to the foregoing two arteries, the following three arteries enter
 
the tympanic cavity: (1) the petrosal branch of the middle meningeal, which
 
enters from the facial canal, into which it passes through the hiatus; (2) the
 
tympanic branch of the ascending pharyngeal, which accompanies the nerve
 
through the tympanic canaliculus; and (3) the tympanic branch of the internal
 
carotid, which enters by a minute foramen on the posterior wall of the ascending
 
part of the carotid canal in company with a sympathetic twig from the carotid
 
plexus.
 
 
 
The veins of the tympanum pass to the pterygoid plexus, the superior petrosal
 
sinus, the internal jugular vein, and the pharyngeal plexus.
 
 
 
Nerves of the tympanum are described on pp. 1325 and 1400.
 
 
 
Internal Ear.
 
 
 
The internal ear is the essential part of the organ of hearing, and
 
is known as the labyrinth from its remarkable complexity. It consists
 
of two parts—namely, the osseous labyrinth and the membranous
 
labyrinth.
 
 
 
Osseous Labyrinth.
 
 
 
The osseous labyrinth is a cavity situated within the petrous part
 
of the temporal bone, and is divided into three parts—namely, the
 
vestibule, the semicircular canals, and the cochlea. These divisions
 
are lined with a delicate periosteum, between which and the contained
 
membranous labyrinth there is a clear fluid, called the perilymph.
 
 
 
Vestibule.—The vestibule is the central division of the osseous
 
labyrinth. The semicircular canals lie behind it, and the cochlea is
 
situated in front of it. In the lateral wall is the fenestra vestibuii, which
 
is occupied by the foot-piece of the stapes and its annular ligament.
 
The medial wall has anteriorly a depression called the fovea spherica
 
or spherical recess, which corresponds to the lamina cribrosa at the
 
deep end of the meatus auditorius internus. It is pierced by apertures
 
for the passage of filaments of the auditory nerve to the saccule.
 
Behind and above the fovea spherica there is a ridge, called the vestibular crest, which lies obliquely. Posteriorly it bifurcates, and
 
between its two divisions there is a small depression, called the cochlear
 
recess, in which are openings for nerve filaments to the canalis cochlese.
 
Anteriorly it becomes somewhat triangular, and forms a pyramid,
 
which is pierced by nerves to the utricle.
 
 
 
The roof of the vestibule, behind and above the crista vestibuii,
 
has an oval depression, called the elliptical recess, which encroaches on
 
the inner wall and lodges the recess of the utricle. It is pierced by
 
nerves to the ampulke of the superior and external semicircular canals.
 
Below the fovea elliptica is the opening of the aqueduct of the vesti
 
 
 
1684
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
bule, which leads to the posterior surface of the petrous part of the
 
temporal bone about J inch external to the orifice of the meatus
 
auditorius internus. It transmits the ductus endolymphaticus and
 
a minute vein.
 
 
 
Anteriorly the vestibule communicates with the scala vestibuli
 
of the cochlea, and posteriorly are the five openings of the semicircular
 
canals.
 
 
 
Semicircular Canals.—The osseous semicircular canals are situated
 
behind the vestibule. They are three in number—superior, posterior,
 
 
 
 
 
Cupola of Cochlea
 
Petrous part of Tern- 5
 
 
 
poral Bone
 
 
 
 
 
Facial Canal
 
A
 
 
 
 
 
 
 
Superior Semicircular Canal
 
 
 
 
 
Fenestra Vestibuli
 
 
 
Lateral Semicircular
 
Canal
 
 
 
 
 
Posterior Semicircular
 
Canal
 
 
 
Vestibule
 
 
 
 
 
Fenestra Cochleae
 
 
 
 
 
_ Superior Semicircular Canal
 
 
 
 
 
Inner Wall of Canal '
 
of Cochlea
 
 
 
Helicotrema
 
 
 
 
 
Lamina Spiralis
 
 
 
 
 
Crus Commune of Sup. and
 
Post. SemicircularCanals
 
 
 
 
 
Posterior Semicircular
 
Canal
 
 
 
Lateral Semicircular
 
Canal
 
Elliptical Recess
 
\ Crista Vestibuli
 
Spherical Recess
 
 
 
 
 
1 \ .
 
 
 
1 '
 
 
 
> Orifice of Aqueductus Vestibuli
 
Recessus Cochlearis
 
 
 
 
 
Fenestra Cochleae
 
Scala T.ympani Scala Vestibuli
 
 
 
Fig. 1035. —The Osseous Labyrinth of the Left Side (Lateral View).
 
A, entire; B opened (Hirschfeld and Leveille; B, modified).
 
 
 
 
 
and lateral—and they open into the vestibule by five circular apertures,
 
the contiguous ends of the superior and posterior canals having a
 
common orifice. Each canal forms about two-thirds of a circle, and
 
each presents at one end an enlargement, called the ampulla. The
 
superior semicircular canal occupies a vertical position, and lies transversely as regards the long axis of the petrous part of the temporal
 
bone, giving rise to the eminentia arcuata on its superior surface.
 
Its ampullary end (antero-external) opens independently into the upper
 
part of the vestibule above the ampullary orifice of the external canal.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
THE EAR
 
 
 
 
 
1685
 
 
 
 
 
Its non-ampullary end unites with the non-ampullary end of the
 
posterior canal to form the crus commune, and the two open by a
 
common orifice into the vestibule. The posterior semicircular canal
 
arches backwards towards the posterior surface of the pars petrosa,
 
with which it is almost parallel, and, like the superior, it occupies a
 
vertical position. Its ampullary end (inferior) opens independently
 
into the lower and back part of the vestibule, and its non-ampullary
 
end, as just stated, joins that of the superior canal. The lateral
 
semicircular canal arches outwards, and occupies a horizontal position.
 
Its extremities are independent of those of the other two canals,
 
and they open by separate apertures into the upper and back part
 
of the vestibule. Its ampullary end is in front.
 
 
 
Cochlea.—The osseous cochlea is situated in front of the vestibule.
 
It consists of a tube coiled spirally upon itself, like a snail s shell,
 
 
 
 
 
 
 
Fig. 1036. _Median Section of the Left Osseous Cochlea of Man
 
 
 
from Apex to Base (Arnold).
 
 
 
 
 
S.V. Scala Vestibuli
 
S.T. Scala Tympani
 
 
 
 
 
L.S.O. Lamina Spiralis Ossea
 
C.C. Central Canal of Modiolus
 
 
 
 
 
M.A.I. Internal Auditory Meatus
 
 
 
 
 
and is conical. Its base is opposite the lamina cribrosa at the deep
 
end of the meatus auditorius interims; and its apex, known as the
 
cupola is directed outwards and slightly forwards towards the canal
 
which contains the tensor tympani muscle. Its length from base to
 
apex is about i inch. It consists of (1) a winding tube, called the
 
spiral canal of the cochlea ; (2) a central pillar, called the modiolus,
 
round which the spiral canal turns; and (3) a thin plate of bone, called
 
the osseous spiral lamina, which winds spirally round the modiolus
 
and projects into the spiral canal of the cochlea. . .
 
 
 
The spiral canal of the cochlea (cochlear canal or tube) winds round
 
the modiolus which forms its inner wall. It describes two and threenuarter turns, and its basal turn or coil gives rise to the promontory on
 
the inner wall of the tympanum. At the cupola it ends in a blind
 
extremity. It gradually diminishes in size from base to cupola; its
 
 
 
 
 
 
 
i686
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
length is about 32 millimetres; and its diameter is about 2 millimetres
 
at the base, where it is greatest.
 
 
 
The modiolus is the central pillar round which the spiral canal of
 
the cochlea turns, and it forms the inner wall of that canal. It commences at the cochlear area of the lamina cribosa at the deep end of the
 
internal auditory meatus, and extends almost to the cupola, gradually
 
tapering. It is traversed by minute canals for branches of the cochlear
 
division of the auditory nerve. One of these canals occupies the
 
centre of the modiolus, and is called the central canal of the modiolus.
 
This canal begins at the foramen centrale of the cochlear area of the
 
lamina cribrosa, and it transmits the nerve-filaments for the apical
 
coil. The other canals, which have no special name, commence at
 
the tractus spiralis foraminosus of the cochlear area of the lamina
 
cribrosa, and they transmit the nerve-filaments for the other coils—
 
middle and basal. At successive levels these canals change their
 
direction, and pass outwards to the attached margin of the lamina
 
spiralis, to be presently described. Here they coalesce and form a
 
winding canal, called the spiral canal of the modiolus, which lodges
 
the spiral ganglion or ganglion of Corti. From this canal secondary
 
canals for nerve-filaments pass into the lamina spiralis.
 
 
 
The osseous spiral lamina is a thin plate of bone, which winds
 
spirally round the modiolus, to which it is attached. It projects from
 
the modiolus into the spiral canal of the cochlea throughout the windings
 
of the latter, and it extends for about half-way towards the outer wall
 
of the cochlear canal. It divides that canal incompletely into two
 
passages or scalar —an upper or scala vestibuli, and a lower or scala
 
tympani, the commencement of which is at the fenestra cochleae.
 
Close to the cupola the lamina spiralis terminates in a hook-like process,
 
called the hamulus. The spiral lamina consists of two plates of bone,
 
between which there are canals for nerve-filaments, these canals being
 
offsets of the spiral canal of the modiolus, which, as has been said,
 
contains the spiral ganglion or ganglion of Corti. They extend to the
 
free margin of the spiral lamina. The free margin of the lamina
 
spiralis is, in the recent state, attached to the outer wall of the spiral
 
canal of the cochlea by means of the basilar membrane or basilar
 
lamina, and the scala vestibuli and scala tympani are now completely
 
separated, except in the region of the hamulus, where they communicate
 
through an opening, called the helicotrema.
 
 
 
The lamina cribrosa, at the deep end of the internal auditory
 
meatus, will be found described in connection with the temporal
 
bone (p. 190).
 
 
 
At the lower end of the scala tympani is the upper opening of the
 
aqueductus cochleae, which passes downwards and medially to the
 
posterior border of the petrous part of the temporal bone. It transmits
 
a small vein to the inferior petrosal sinus, and establishes a communication between the scala tympani and the subarachnoid space.
 
 
 
 
 
 
 
THE EAR
 
 
 
 
 
1687
 
 
 
 
 
Membranous Labyrinth.
 
 
 
The membranous labyrinth is situated within the osseous labyrinth,
 
and its constituent parts receive the terminal branches of the auditory
 
nerve. It is separated from the periosteal lining of the osseous labyrinth by the perilymph, and it contains the fluid known as the endolymph. In the case of the vestibule and the osseous semicircular
 
canals the. membranous labyrinth corresponds more or less with
 
them; but in the case of the osseous cochlea it forms part of the septum
 
between the scala tympani and scala vestibuli, and contains a passage
 
called the membranous canal of the cochlea (ductus cochleae).
 
 
 
 
 
 
 
Fig. 1037. —Diagram of Membranous Labyrinth.
 
 
 
Vestibular Part of the Membranous Labyrinth.—The vestibule
 
contains two membranous sacs—namely, the utricle and the saccule
 
 
 
_which are in close contact, but do not communicate with each other
 
 
 
directly. These sacs contain endolymph.
 
 
 
The utricle is the larger of the two sacs, and into it the membranous
 
semicircular ducts open. It occupies the upper and back part of the
 
vestibule, a portion of it, known as the recessus utriculi, lying in the
 
fovea elliptica. Near the crista vestibuli the wall of this recess receives
 
fibres of the auditory nerve and is thickened, this part of it being called
 
the macula utriculi. From the anterior and medial part of the utricle
 
a minute canal, called the ductus utriculi («ductus utriculo-saccularis ),
 
passes to join the ductus sacculi, and so form the ductus endolymphaticus (see Fig. 1037).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1688
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
The saccule, which is somewhat oval, lies in front of the utricle,
 
and occupies the fovea spherica, where it is near the opening leading
 
into the scala vestibuli of the cochlea. Through the openings of the
 
fovea spherica it receives filaments of the auditory nerve, and this
 
portion of the saccule, being thickened, is known as the macula sacculi.
 
Interiorly the saccule is connected with a small canal, called the
 
ductus reuniens, which opens into the canal of the cochlea, or ductus
 
cochlearis, not far from its closed vestibular end. From the posterior
 
part of the saccule a minute canal, called the ductus sacculi, passes off,
 
which is soon joined by the ductus utriculi, and so the ductus endolymphaticus is formed. This latter duct traverses the aqueductus
 
vestibuli, and, having reached the posterior surface of the petrous
 
part of the temporal bone, it ends in a small blind dilatation, called the
 
saccus endolymphaticus , which lies beneath the dura mater. The saccule
 
and utricle are thus indirectly connected by means of the ductus sacculi
 
and ductus utriculi; and the saccule communicates with the ductus
 
cochlearis by means of the ductus reuniens.
 
 
 
Semicircular Ducts.—The membranous semicircular ducts correspond in outline to the osseous semicircular canals, within which they
 
lie; they form about two-thirds of a circle, and each has an ampulla
 
at one end, which is situated within the ampulla of the osseous canal.
 
They are elliptical in transverse section, and open into the utricle by
 
five orifices, the non-ampullated ends of the superior and posterior
 
canals being united, so that these two open by a common orifice
 
forming the crus commune. The convex wall of each canal is attached
 
to the periosteal lining of the osseous canal, whilst the concave wall is
 
practically free from the osseous wall, and is bathed by the perilymph.
 
These canals contain endolymph.
 
 
 
Structure.—The walls of the utricle, saccule, and membranous
 
semicircular canals consist of three layers: an outer or fibrous layer,
 
which is vascular; a middle layer, or membrana propria, which is translucent; and an inner or epithelial layer. In each ampulla the middle
 
layer, or membrana propria, projects into the cavity of the canal from
 
the peripheral wall, this projecting part being known as the septum
 
transversum. It partially divides the interior of the ampulla into two
 
compartments, and its free margin, which is covered by the auditory
 
epithelium, is called the crista acustica or ampullaris. The epithelial
 
layer consists of a single stratum of squamous cells, except in those
 
regions to which the filaments of the auditory nerve are distributed. These regions are as follows: (i) the macula (acustica)
 
utriculi; (2) the macula (acustica) sacculi; and (3) the crista of each
 
ampulla.
 
 
 
The macula utriculi is the thickened part of the antero-inferior wall
 
of the recessus utriculi, and is lined with auditory epithelium. The
 
macula is covered by calcareous particles, called otoconia, which
 
consist of crystals of calcium carbonate. The macula sacculi is the
 
thickened part of the anterior wall of the saccule, and is also lined with
 
auditory epithelium covered by otoconia. The crista ampullaris, as
 
 
 
 
 
THE EAR
 
 
 
 
 
1689
 
 
 
 
 
we have seen, is the free margin of the septum trailsversum in each
 
ampulla, and is covered by auditory epithelium.
 
 
 
The auditory epithelium is of the columnar variety, and consists of
 
two kinds of cells, auditory and sustentacular. The auditory cells are
 
nucleated, and each is provided at its free extremity with a slender,
 
tapering, hair-like filament, which projects into the cavity. These
 
filaments are sometimes spoken of collectively as auditory hairs, and
 
the cells are hence called hair-cells. Their deep extremities fall short
 
of the membrana propria. The sustentacular cells lie between the haircells, and are elongated and nucleated. Their deep extremities are
 
attached to the membrana propria, and their free extremities give rise
 
to a kind of limiting membrane. The auditory nerve-fibres pierce
 
the membrana propria, and, having lost their medullary sheaths, the
 
axons end in arborizations round the deep ends of the auditory or
 
hair cells.
 
 
 
Superior Semicircular Duct
 
 
 
 
 
Lateral Semicircular Duct i
 
 
 
 
 
Posterior Semicircular Duct
 
 
 
 
 
 
 
Facial Nerve
 
 
 
 
 
Crus Commune of Superior and
 
' l Posterior Semicircular Ducts
 
 
 
j r Ampulla
 
 
 
_ l Nerve to Ampulla
 
Nerve to Utricle
 
~ . Nerve to Saccule
 
_ Cochlear Nerve
 
 
 
 
 
Fig. 1038. —The Membranous Semicircular Ducts, showing the Distribution of the Branches of the Auditory Nerve to their Ampullae
 
 
 
(Breschet).
 
 
 
Membranous Cochlea.—The membranous cochlea is situated within
 
the osseous cochlea, and fills the gap which is left by the lamina
 
spiralis. It consists of two membranes, the basilar membrane and the
 
vestibular membrane (membrane of Reissner, Fig. 1040), which enclose
 
between them the ductus cochlearis, or scala media. 1 he osseous
 
cochlea in the recent state is therefore divided into three spiral
 
passages—the scala tympani, the scala vestibuli, and the ductus
 
cochlearis. The scala vestibuli is continuous with the scala tympani
 
at the cupola through an aperture, called the helicotrema ; and at the
 
base of the cochlea it opens upon the anterior wall of the vestibule.
 
The scala tympani begins at the fenestra cochleae, and in the recent
 
state is separated from the tympanic cavity by the secondary membrane of the tympanum. The scala media, or ductus cochlearis,
 
communicates near its lower end with the saccule by means of the ductus
 
reuniens. The scala vestibuli and scala tympani contain perilymph,
 
which is continuous with the perilymph of the vestibule and osseous
 
semicircular canals. The scala media contains endolymph, which is
 
continuous with that of the saccule,
 
 
 
 
 
 
 
 
 
1690
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
Basilar Membrane.—The basilar membrane extends from the free
 
margin of the lamina spiralis to the crista basilaris, or lower part of
 
the spiral ligament, a thickening of the periosteum of that part of the
 
outer wall of the cochlea which forms the outer wall of the scala media,
 
or ductus cochlearis. It separates the ductus cochlearis from the scala
 
tympani, and is divisible into two zones, inner and outer. The inner
 
is called the zona arcuata, and supports the spiral organ. The outer
 
is known as the zona pectinata, and extends from the foot-plates of
 
the outer rods of this organ to the crista basilaris. The basilar membrane consists of a homogeneous membrana propria, with fibres embedded in it, the fibres being most numerous in the zona pectinata.
 
 
 
Vestibular Membrane, or Membrane of Reissner.—This is a delicate
 
membrane which extends from the upper surface of the lamina spiralis
 
a short distance from its free margin to the outer wall of the cochlea,
 
where it is attached to the periosteum a little above the outer attachment of the basilar membrane. It separates the cochlear duct from the
 
scala vestibuli, and consists of very delicate connective tissue lined on
 
each side with a single layer of squamous epithelium.
 
 
 
 
 
Osseous Spiral Lamina
 
 
 
 
 
Vestibular Membrane
 
Basilar Membiane
 
 
 
 
 
Scala Vestibuli
 
 
 
Ductus Cochlearis
 
 
 
 
 
Sc' NYll ESy/: ,'-.;
 
 
 
| Scala Tympan*
 
 
 
 
 
 
 
 
 
Fig. 1039.
 
 
 
 
 
-Vertical Section of the Cochlea of a Fcetal Calf, showing
 
THE SCALAE AND MODIOLUS (KoLLIKER).
 
 
 
 
 
The scala media, or ductus cochlearis, is situated between the
 
basilar membrane and the vestibular membrane. It is triangular in
 
transverse section, and has a roof, an outer wall, and a floor. The
 
roof is formed by the vestibular membrane (see Fig. 1040). The
 
outer wall is the wall of the cochlea and its periosteum, between the
 
external attachments of the basilar membrane and the vestibular
 
membrane. The periosteum in this region is much thickened, and
 
forms the spiral ligament of the cochlea, the lower part of which gives
 
rise to the crista basilaris. The floor is formed by the basilar membrane, and a part of the upper surface of the lamina spiralis. It has
 
been seen that the basilar membrane separates the ductus cochlearis
 
from the scala tympani. The ductus ends above in a closed extremity
 
at the cupola, and it has a similar ending at the base of the cochlea.
 
Near its lower blind extremity it receives the ductus reuniens, by
 
which it communicates with the saccule.
 
 
 
It has just been shown that part of the floor of the cochlear duct
 
is formed by some of the lamina spiralis. In the recent state it is
 
of some thickness, which is due to a thickening of its periosteal
 
 
 
 
 
/
 
 
 
 
 
 
 
 
 
THE EAR
 
 
 
 
 
1691
 
 
 
 
 
covering. This fibrous thickening forms the limbus laminae spiralis
 
(see Fig. 1040).
 
 
 
Its outer margin is crescentic, the deep notch being called the sulcus lamince
 
spiralis. The sulcus has two lips, upper and lower. The upper is called the
 
labium vestibulare, the upper surface of which is marked by several interlacing
 
prominences and grooves. At the free margin of this labium the prominences
 
assume the form of tooth-like projections, which are known as the auditory
 
teeth. The lower lip of the sulcus is called the labium tympanicum. It is continued into the basilar membrane, and is perforated by a great number of apertures
 
for the branches of the cochlear division of the auditory nerve.
 
 
 
Spiral Organ (of Corti).—Over the upper surface of the inner part
 
(zona arcuata) of the basilar membrane the epithelium undergoes
 
 
 
 
 
 
 
Fig. 1040.—The Organ of Corti (Wiedersheim, after Lavdowsky).
 
 
 
 
 
1. Spiral Ligament
 
 
 
2. Limbus
 
 
 
3. Sulcus Spiralis
 
 
 
4. Inner Rod of Corti
 
 
 
5. Outer Rod of Corti
 
 
 
6. Tunnel of Corti
 
 
 
7. Phalangeal Process of Outer Rod
 
 
 
8. Inner Hair-cells
 
 
 
 
 
9. Outer Hair-cells
 
 
 
10. Cells of Deiters
 
 
 
11. Lamina Reticularis
 
 
 
12. Cells of Hensen
 
 
 
13. Cells o Claudius
 
 
 
14. Spiral Ganglion
 
 
 
15. Cochlear Nerve
 
 
 
16. Nerve-fibres to Hair-cells
 
 
 
 
 
remarkable modification, and gives rise to the spiral organ or organ
 
of Corti. The constituent parts of this very complicated organ are as
 
 
 
follows:
 
 
 
1 The rods of Corti. 4. The cells of Hensen and of Claudius.
 
 
 
2 The auditory or hair cells. 5 - The lamina reticularis.
 
 
 
3! The cells of Deiters. 6. The membrana tectona.
 
 
 
The rods of Corti are arranged in two rows, inner and outer (see
 
Fig 1041). Each rod consists of a foot-plate or base, an intermediate
 
portion, and a head. The foot-plate, which is expanded, rests upon
 
the zona arcuata of the basilar membrane, and the foot-plates of the
 
inner rods are separated from those of the outer rods by a slight
 
interval. As the rods rise the intermediate portions of the inner and
 
 
 
 
 
 
 
 
 
 
 
 
 
1692
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
outer rods incline towards each other, and the heads of the two sets
 
of rods come into contact. In this manner a triangular tunnel is
 
enclosed between the two sets of rods and the basilar membrane,
 
which is called the tunnel of Corti. This extends along the entire
 
length of the ductus cochlearis.
 
 
 
 
 
phalangeal
 
 
 
PROCESS
 
 
 
 
 
IfSNER ROD
 
 
 
 
 
 
 
BASILAR. MEMBRANE
 
 
 
 
 
The inner rods are more numerous than the outer, there being from
 
5,000 to 6,000 of the former and about 4,000 of the latter. They
 
incline upwards and outwards. The head of each has a concavity on
 
its outer side, above and below which there is a projecting portion, so
 
 
 
that it resembles the upper extremity
 
of the ulna, with its great sigmoid
 
cavity and olecranon and coronoid
 
processes. The concavity on the head
 
of the inner rod receives the round
 
head of the outer rod. Finally, the
 
tic. 1041. A Pair of Rods of inner rods are shorter than the outer.
 
Corti from the Rabbit’s Coch- The ou + pr rn d<? lpcc nnmprrmQ
 
 
 
lea (Side View, highly mag- An ? ouler * oas j ^ re . Aess nui ? e 5 , 0US
 
 
 
nified) (Schafer, in Quain’s ? nd lon § er than the inner, and they
 
 
 
‘Anatomy’). ~ incline upwards and inwards. The
 
 
 
head of each is divisible into two
 
parts—inner and outer. Ihe inner part is round, and is received
 
mto the concavity on the outer aspect of the head of the inner rod.
 
The outer part is prolonged into a beak-like projection, called the
 
phalangeal process, which forms part of the lamina reticularis, to be
 
presently described.
 
 
 
The auditory or hair cells are arranged in two sets—inner and
 
outer. Ihe inner hair-cells lie internal to the row of inner rods, and
 
form a single row. They are from 3,000 to in number. Their
 
 
 
free extremities, which lie close to the heads of the inner rods, are each
 
provided with a tuft of short, hair-like filaments. The deep, nucleated
 
ends of the cells are related to the terminal arborizations of nervefibres. Internal to the row of inner hair-cells there are two or more
 
rows of columnar cells, which are continuous with the columnar
 
epithelium of the sulcus spiralis laminae. The outer hair-cells are
 
disposed in three or four rows external to the outer row of rods. They
 
are much more numerous than the inner hair-cells. Their free extremities, like those of the inner cells, are each provided with a tuft
 
of short, hair-like filaments, and their deep, nucleated ends are related
 
to the terminal arborizations of nerve-fibres.
 
 
 
 
 
1 he cells of Deiters, which are sustentacular, are situated between
 
the rows of outer hair-cells. Each cell is nucleated and contains a
 
slender filament, known as the sustentacular filament or phalangeal
 
process. This filament is attached by its base to the basilar membrane, and is prolonged into the tapering upper end of the cell. It
 
terminates in an expansion, which forms a phalanx of the lamina
 
reticularis, to be presently described.
 
 
 
The cells of Hensen are disposed as a continuous layer external
 
to the lamina reticularis.
 
 
 
 
 
 
 
 
 
THE EAR 1693
 
 
 
External to the cells of Hensen there are the cubical or columnar
 
cells of Claudius: these are merely an epithelial lining layer.
 
 
 
The reticular lamina extends between the heads of the rods of
 
Corti and the cells of Hensen. It consists of phalanges, which are
 
arranged in two (or more) rows—inner and outer. The phalanges of
 
the inner row are formed by the phalangeal processes of the heads of the
 
outer rods of Corti. The phalanges of the outer row (or rows) are
 
formed by the phalangeal processes of the cells of Deiters. Between
 
the phalanges there are openings through which the outer ends of
 
the outer hair-cells, with their crescentic tufts of hair-like filaments,
 
project.
 
 
 
The membrana tectoria, or membrane of Corti, which is elastic,
 
is the most superficial structure in connection with the spiral organ.
 
It extends from the limbus spiralis near, and external to, the attachment of the vestibular membrane to the region of the outer hair-cells.
 
It covers (1) the limbus laminae spiralis; (2) the labium vestibulare,
 
 
 
 
 
 
 
 
 
- Hehcotrema
 
 
 
 
 
Scala Vestibuli
 
 
 
 
 
Membranous Spiral
 
Lamina
 
 
 
 
 
Scala Tympani
 
 
 
 
 
1
 
 
 
1
 
 
 
Expansion of Cochlear Nerve
 
 
 
Fig. 1042.—Section of the Cochlea, showing the Distribution of the
 
Cochlea Branch of the Auditory Nerve (magnified) (Hirschfeld
 
and Reveille).
 
 
 
and the auditory teeth; (3) the sulcus laminae spiralis; (4) the inner
 
hair-cells; (5) the inner and outer rods of Corti; (6) the cells of Deiters;
 
and (7) the lamina reticularis.
 
 
 
Auditory Nerve.—The auditory nerve, within the meatus auditorius
 
internus, breaks up into two divisions—vestibular and cochlear.
 
 
 
The vestibular nerve, as it traverses the meatus auditorius internus, has a gangliform enlargement, the vestibular ganglion, and
 
divides into three branches. These enter the vestibule through the
 
foramina in the superior vestibular area of the lamina cribrosa at the
 
deep end of the internal meatus. They are distributed to the macula
 
utriculi and to the cristae acusticas of the ampullae of the superior
 
and external semicircular canals.
 
 
 
The cochlear nerve in the meatus auditorius internus divides into
 
two branches—one to the macula sacculi, and the other to the crista
 
of the ampulla of the posterior semicircular canal. The filaments of
 
the former, which has a gangliform enlargement, pass through the foramina in the inferior vestibular area of the lamina cribrosa, and the
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
1694
 
 
 
latter passes through the foramen singulare in the lamina cribrosa.
 
The cochlear nerve, having parted with these two branches, breaks
 
up into filaments which pass through the foramina of the cochlear
 
area of the lamina cribrosa, and so reach the base of the modiolus
 
of the cochlea. They traverse the canals of the modiolus, from which
 
they pass into the canals between the two layers of the lamina spiralis.
 
In doing so they have to cross the spiral canal of the modiolus, which
 
is situated close to the attached margin of the lamina spiralis. This
 
canal contains a ganglion, called the spiral ganglion, which follows
 
the windings of the canal, and contains bipolar nerve-cells. As the
 
auditory fibres pass from the canals of the modiolus into those of
 
the lamina spiralis the course of each fibre is probably interrupted
 
by a bipolar cell of the spiral ganglion. The nerve-fibres, leaving
 
these bipolar cells, traverse the canals between the two layers of the
 
lamina spiralis. Having lost their medullary sheaths, they pass
 
through the foramina of the labium tympanicum on the outer margin
 
of the limbus spiralis, and enter the basilar membrane, where they
 
end in arborizations which are connected with the inner and outer
 
hair-cells.
 
 
 
Blood-supply of the Labyrinth.—The labyrinth derives its blood
 
from the internal auditory, which is a branch of the basilar artery
 
or of the anterior inferior cerebellar. The vessel traverses the meatus
 
auditorius internus, and divides at its deep end into two branches—
 
vestibular and cochlear. The vestibular artery supplies the utricle,
 
saccule, and semicircular canals, and the cochlear artery supplies the
 
cochlea.
 
 
 
The veins of the labyrinth ultimately join to form one vessel, called
 
the internal auditory vein, which opens into the inferior petrosal
 
sinus. The aqueductus cochleae and the aqueductus vestibuli each
 
transmit a vein; that which passes through the former joins the inferior
 
petrosal sinus or the bulb of the internal jugular vein, and that which
 
passes through the latter opens into the superior petrosal sinus.
 
 
 
 
 
Development of the Ear.
 
 
 
Internal Ear—Membranous Labyrinth. —The membranous labyrinth is
 
developed from the surface ectoderm in a manner similar to the development
 
of the crystalline lens. Over a circumscribed area, corresponding to the upper
 
end of the first visceral cleft, and upon the side of the hind-brain, the ectoderm
 
becomes thickened and invaginated. A depression is thus formed, which is
 
called the auditory pit. This pit becomes deepened, its mouth becomes constricted, and its lips, coming together, unite. The auditory pit then becomes
 
transformed into a closed sac, called the auditory or otic vesicle, or otocyst.
 
The auditory vesicle now becomes isolated from the surface ectoderm, and sinks
 
into the adjacent mesoderm, taking up a position close to the side of the hindbrain.
 
 
 
The auditory vesicle, which is at first almost spherical, soon becomes pyriform, this being due to the formation of a process, called the recess of the labyrinth
 
or vestibule, which is prolonged from its dorsal wall. As this process lengthens
 
it gives rise to the ductus endolymphaticus, which occupies the aqueductus
 
vestibuli of the petrous portion of the temporal bone. The expanded terminal
 
 
 
 
 
 
 
THE EAR
 
 
 
 
 
1695
 
 
 
part of the ductus endolymphaticus is called the saccus endolymphaticus, and it
 
lies underneath the dura mater. The ventral aspect of the vesicle gives off a
 
tapering diverticulum, which gives rise to the ductus cochlearis, or scala media,
 
of the cochlea. This duct describes a bend, within which lies the cochlear
 
ganglion of the cochlear division of the auditory nerve. As the duct elongates
 
it continues to bend in a spiral manner, and so the ductus cochlearis is formed.
 
The cochlear ganglion elongates, and follows the spiral turns of the duct, from
 
which circumstance the ganglion is known as the ganglion spirale.
 
 
 
The three semicircular ducts are developed from the upper or cephalic part
 
of the auditory vesicle, this part representing the future utricle. This portion
 
of the vesicle presents two folds—vertical and horizontal. From the vertical
 
fold the superior and posterior semicircular canals are formed, whilst the horizontal fold gives rise to the lateral semicircular canal.
 
 
 
The auditory vesicle now becomes transversely constricted, and is divided
 
into two sacs—large and small. The large sac is called the utricle, from which
 
the semicircular ducts have just been developed. The small sac is called the
 
saccule, from which the ductus cochlearis has been developed. The portion
 
of this duct which communicates with the saccule becomes constricted, and
 
forms the canalis reuniens of Hensen.
 
 
 
The constriction which completely divides the auditory vesicle into utricle
 
and saccule also involves the vesicular end of the ductus endolymphaticus, and
 
divides it into two ducts, called the ductus utriculi and ductus sacculi. This
 
arrangement constitutes the only communication which now exists between the
 
utricle and the saccule.
 
 
 
As stated, the cochlear ganglion, or ganglion spirale, of the cochlear division
 
of the auditory nerve lies within the spiral turns of the ductus cochlearis. As
 
the osseous cochlea becomes formed, the ganglion spirale comes to occupy the
 
spiral canal of the modiolus. The vestibular ganglion of the vestibular division
 
of the auditory nerve lies in the internal auditory meatus after the completion
 
of ossification.
 
 
 
The membranous labyrinth, hitherto considered, is entirely epithelial.
 
Certain of its epithelial cells undergo important specializations to fit them for
 
sensorial purposes. These cells form six groups in definite regions. These groups
 
are as follows: (1) The crista acustica ampullaris, of which there are three, one in
 
the ampulla of each of the three epithelial semicircular canals; (4) the macula
 
(1 acustica) utriculi’, (5) the macula ( acustica) sacculi', and (6) the spiral organ {of
 
Corti), specialized from the epithelial ductus cochlearis. The groups connected
 
with the ampullae of the semicircular canals, the utricle, and the saccule, receive
 
their nerve-fibres from the vestibular ganglion of the vestibular division of the
 
auditory nerve. The organ of Corti receives its nerve-fibres from the cochlear
 
ganglion, or ganglion spirale, of the cochlear division of the auditory nerve.
 
 
 
Osseous Labyrinth. —The membranous labyrinth is surrounded by mesodermic
 
tissue, which becomes disposed in four layers. These layers, from within outwards,
 
may be spoken of as (1) the connective-tissue layer, (2) the gelatinous layer,
 
(3) the perichondrial layer, and (4) the cartilaginous layer. The connectivetissue layer forms the connective tissue of the various parts of the epithelial
 
labyrinth. The fibrous tissue of the gelatinous layer acquires vacuoles, and gives
 
place to the various perilymphatic spaces, which contain a fluid called the perilymph. In the case of the cochlea, the scala vestibuli and scala tympani alone
 
contain perilymph, the cochlear duct containing endolymph. The perichondrial
 
layer forms the lining perichondrium of the periotic cartilaginous capsule, and
 
subsequently becomes the lining periosteum of the osseous labyrinth. The
 
cartilaginous layer forms the periotic cartilaginous capsule, which undergoes
 
ossification, and gives rise, amongst other parts, to the osseous labyrinth, which
 
jg q£ i ar ger size than the membranous labyrinth. The osseous semicircular canals
 
conform in shape to the membranous semicircular ducts, but are of larger size.
 
The osseous vestibule differs from the membranous vestibule in being a single
 
osseous case, whereas its contents are the utricle and the saccule.
 
 
 
Whilst the perilymph lies external to the membranous labyrinth, the interior
 
 
 
 
 
1696
 
 
 
 
 
A MANUAL OF ANATOMY
 
 
 
 
 
of the semicircular ducts, utricle, saccule, and scala media contain endolymph,
 
the latter being in communication with the saccule by means of the canal is
 
reuniens.
 
 
 
The middle ear or tympanum and pharyngo-tympanic tube (see p. 73 et seq.)
 
 
 
are developed from the tubo-tympartic recess of the pharynx. This is the widest
 
part of the early pharynx, opposite the second and third arches, and by the
 
time the embryo has reached the second month of development the recess is
 
definitely indicated; it projects laterally with its contained cavity, compressed
 
dorso-ventrally, widely open into the general pharyngeal cavity. Its roof
 
supports the otic capsule, while the outer parts of the first two visceral grooves
 
are seen in its floor, with the second arch between them. It is bounded in
 
front by the first arch, and caudally by the third arch. The first lateral pouch,
 
on its lateral edge, is in contact with the persistent upper end of the first outer
 
groove; the second pouch, which has lost contact, is at its postero-lateral angle.
 
The recess deepens, and the third arch grows forward, cutting off the outer part
 
of the cavity from the pharynx and narrowing the anterior part, which still
 
remains continuous with the pharynx; the outer and larger part is the early
 
tympanum, and the constricted front portion becomes the tube.
 
 
 
The otic capsule enlarges and chondrifies, and as it grows depresses the
 
inner part of the tympanum, slightly rotating it, so that its former roof now
 
becomes its inner wall, applied to the surface of the capsule. Its floor, also
 
rotated, now slopes downwards and medially, and is in close relation with the
 
meatal plate, a cellular ingrowth from the upper end of the first outer groove;
 
this has grown in below the tympanum, and by a later process of hollowing
 
forms the ectodermal lining of the outer meatus and membrane.
 
 
 
Meckel’s cartilage develops in the mesoderm of the first arch, therefore
 
antero-lateral to the recess, in front of the position of the first pouch. It sends
 
an extension over the pouch to invade the second arch area behind this, passing
 
under the floor between the endoderm and the meatal plate; this extension forms
 
the basis of the tympanic membrane and the manubrium, and its upper part probably also forms the incus. The hyoid bar (Reichert’s cartilage), the bar of the
 
second arch, is behind this, immediately in front of the second pouch; an exten
 
sion from its upper end over the roof gives rise to the stapes. The stapes becomes
 
associated with the cartilaginous capsule, which has enlarged considerably; the
 
enlargement extends postero-laterally, and leads to the fusion of Reichert’s bar
 
with the capsule (tympano-hyal) and the position of the remnant of the second
 
pouch in the fossula rotunda (fenestra cochleae).
 
 
 
The chorda tympani crosses the first pouch; the level of the early tympanum
 
might roughly be taken as extending up to this nerve. The higher level of the
 
adult cavity is attained by a later extension. In the early condition of the
 
tympanum, the malleus, incus, stapes, and chorda tympani nerve lie embedded
 
in the mesodermic tissue which intervenes between the epithelial or mucous
 
roof of the membranous tympanum and its osseous roof. This mesodermic
 
tissue disappears, and the mucous (originally epithelial) lining of the tympanum
 
now comes into direct contact with the malleus, incus, stapes, and chorda
 
tympani nerve, all of which it encloses within folds. Though these structures
 
apparently lie within the tympanic cavity, this is not their actual position. They
 
are really outside the cavity, inasmuch as they lie external to the mucous lining of
 
the cavity. This may be illustrated by stating that the handle or manubrium
 
of the malleus and the chorda tympani nerve do not lie in the tympanic cavity,
 
but are placed between the middle, or fibrous, layer and the internal, or mucous,
 
layer of the membrana tympani.
 
 
 
External Ear.— AThe external ear consists of (1) the external auditory meatus,
 
including the membrana tympani, and (2) the pinna.
 
 
 
The external auditory meatus is developed from the upper part of the first
 
external or ectodermic furrow, which corresponds in position to the first
 
internal visceral cleft.
 
 
 
The membrana tympani is developed from the closing membrane which
 
separates the first internal visceral cleft from the first external ectodermic furrow.
 
 
 
 
 
THE EAR
 
 
 
 
 
1697
 
 
 
This closing membrane is a trilaminar structure. Its inner layer consists of
 
entoderm; its middle layer of mesoderm; and its outer layer of ectoderm. The
 
membrana tympani, which is developed from it, is therefore trilaminar. The
 
outer layer is ectodermic, and is continuous with the cuticular lining of the external
 
auditory meatus; the middle layer is mesodermic, or fibrous; and the inner layer
 
is entodermic, or mucous, and is continuous with the mucous lining of the
 
tympanic cavity.
 
 
 
The component parts of the pinna are developed from six projections, consisting of mesoderm, covered by ectoderm. These appear on the upper ends
 
of the first and second visceral arches, where these bound the upper part of
 
the first external ectodermic furrow, which gives rise to the external auditory
 
meatus. The helix is developed from two of these tubercles, and each of the
 
other four gives rise to the antihelix, tragus, antitragus, and lobule. The mesodermic tissue of the projections becomes differentiated into connective tissue
 
and cartilage, and the ectoderm covers these.
 
 
 
 
 
107
 
 
 
 
 
GLOSSARY
 
 
 
 
 
Terms still in common use, though now ‘discardedare included in this list,
 
with a certain number of proper names coming in the same category.
 
 
 
 
 
Abdomen, a word of uncertain derivation, but possibly from abdo,
 
I hide or conceal.
 
 
 
Aberrant, wandering from the normal
 
source.
 
 
 
Acervulus, a little heap.
 
 
 
Acervulus cerebri, brain-sand.
 
 
 
Acetabulum, a vessel for holding
 
vinegar; a juggler’s cup. But
 
used by Pliny to signify hipsocket.
 
 
 
Acinus, any juicy berry with stones
 
— e.g., the grape; the kernel in the
 
berry.
 
 
 
Acrocephalous, having a pointed or
 
conical head.
 
 
 
Acromion, the point or summit of
 
the shoulder.
 
 
 
Acusticus, a, um, pertaining to sound,
 
or to the sense of hearing.
 
 
 
Adamantoblast, enamel germ cell.
 
 
 
Adductor canal, subsartorial canal.
 
 
 
Adenoid, glandular.
 
 
 
Aditus, an approach or access.
 
 
 
Adrenal, near to the kidney.
 
 
 
Advehens, carrying to.
 
 
 
Afferent, carrying to.
 
 
 
Agger, a mound or rampart.
 
 
 
Agminated, disposed in columns.
 
 
 
Ala, a wing.
 
 
 
Ala cinera, vagal triangle.
 
 
 
Albicans, white.
 
 
 
Albuginea, whitish.
 
 
 
Alcock’s canal, pudendal canal.
 
 
 
Allantois, sausage-like.
 
 
 
Alveolus, a little trough.
 
 
 
Alveus, a trough.
 
 
 
Amacrine, without a long fibre.
 
 
 
Ambiguus, dark, obscure.
 
 
 
Ameloblast, enamel germ.
 
 
 
Ammonis, cornu, horn of Ammon,
 
who was represented as having
 
the head of a ram.
 
 
 
 
 
Amphiarthrosis, literally, articulation on both sides. Secondary
 
cartilaginous joint (fibro-cartilage).
 
 
 
Ampulla, a flask.
 
 
 
Amygdala, an almond.
 
 
 
Anastomosis, literally, an outlet; the
 
communication of branches of
 
vessels with one another.
 
 
 
Anconeus, pertaining to the elbow.
 
 
 
Ankylosis, bony union between two
 
bones which are normally separate.
 
 
 
Annulus, a little ring.
 
 
 
Ansa, a handle, loop, or brace.
 
 
 
Ansa cervicis, ansa hypoglossi.
 
 
 
Anserinus, pertaining to a goose.
 
 
 
Antecubital, in front of the elbow.
 
 
 
Antibrachium, forearm.
 
 
 
Anticubital fossa, cubital fossa.
 
 
 
Anticus, in front, anterior.
 
 
 
Antinion, opposite to the inion.
 
 
 
Antrum, a cave or cavity.
 
 
 
Antrum of Highmore, maxillary
 
sinus.
 
 
 
Antrum, mastoid, tympanic antrum.
 
 
 
Anus, a ring.
 
 
 
Aorta, literally, the lower end of the
 
trachea; a carrier.
 
 
 
Apertura piriformis, anterior aspect
 
of nose.
 
 
 
Aponeurosis, an expansion from a
 
tendon.
 
 
 
Aponeurosis, lumbar, lumbar fascia.
 
 
 
Aponeurosis, pharyngeal, pharyngobasilar fascia.
 
 
 
Apophysis (‘ grow from ’), a process
 
or swelling on a bone.
 
 
 
Appendix ventriculi laryngis, saccule.
 
 
 
Aqueductus cerebri, aqueduct of
 
 
 
 
 
mid-brain.
 
 
 
Aqueductus Fallopii, facial canal.
 
Arachnoid, like a spider’s web.
 
 
 
1698
 
 
 
 
 
 
 
 
 
GLOSSARY 1699
 
 
 
 
 
Arantii, corpus, nodule (in cusps of
 
aortic and pulmonary valves).
 
 
 
Archenteron, primitive intestine.
 
 
 
Arcuatus, curved.
 
 
 
Area acustica, vestibular area.
 
 
 
Areola, a small open place.
 
 
 
Arnold’s ganglion, otic ganglion.
 
 
 
Arnold’s nerve, tympanic nerve.
 
 
 
Artery, literally, an air vessel; the
 
trachea was known as the arteria
 
aspera; a bloodvessel which carries
 
the blood from the heart.
 
 
 
Arthrodia, from the Greek word
 
meaning * a joint ’; applied to a
 
gliding joint.
 
 
 
Arthrosis, plane joint.
 
 
 
Arytenoid, pitcher-like.
 
 
 
Ascending frontal convolution, precentral convolution.
 
 
 
Ascending parietal convolution, postcentral convolution.
 
 
 
Aspera, rough.
 
 
 
Asterion, a star.
 
 
 
Astragalus, the ankle-bone; a die
 
(pi. dice); talus.
 
 
 
Atlas, a support; refers to Atlas,
 
who carried the earth on his
 
neck.
 
 
 
Atresia, imperforation.
 
 
 
Atrium, the hall in a Roman house.
 
 
 
Attic, epitympanic recess.
 
 
 
Attollens, raising up, elevating.
 
 
 
Attrahens, drawing to or towards.
 
 
 
Auditory, pertaining to the organ, or
 
sense, of hearing.
 
 
 
Auerbach’s plexus, myenteric plexus.
 
 
 
Auricle, the external ear.
 
 
 
Auricle (O.T.), atrium (heart).
 
 
 
Auricular appendix (O.T.), auricle.
 
 
 
Azygos, without a pair, single.
 
 
 
Bacillary, pertaining to a small staff
 
or rod.
 
 
 
Balanus, an acorn.
 
 
 
Barba, a beard.
 
 
 
Bartholin’s duct (great duct of Rivini),
 
 
 
principal sublingual duct.
 
 
 
Basilar, belonging to the base.
 
 
 
Basilic, royal, important.
 
 
 
Basion, base.
 
 
 
 
 
Bechterew, nucleus of, superior
 
vestibular nucleus.
 
 
 
Bell, nerve of, nerve to serratus
 
anterior.
 
 
 
Bellini, ducts of, terminal collecting
 
tubules of kidney.
 
 
 
Biceps, having two heads.
 
 
 
Bicornis, two-horned.
 
 
 
Bicuspid (teeth), pre-molar.
 
 
 
Bigelow, Y-shaped ligament of, iliofemoral ligament.
 
 
 
Biventer, having two bellies.
 
 
 
Bowman’s capsule, capsule of glomerulus.
 
 
 
Bowman’s membrane, anterior elastic lamina of cornea.
 
 
 
Brachium, the arm.
 
 
 
Brachium conjunctivum, superior
 
cerebellar peduncle.
 
 
 
Brachium pontis, middle cerebellar
 
peduncle.
 
 
 
Brachycephalic, short-headed.
 
 
 
Bregma, from a Greek verb meaning
 
‘ to moisten/
 
 
 
Broca, area of, parolfactory area.
 
 
 
Broca, band of, diagonal band.
 
 
 
Bronchiole, a little bronchus.
 
 
 
Bronchus, literally, a draught; the
 
windpipe.
 
 
 
Bryant’s triangle, (1) horizontal line
 
from anterior superior spine;
 
(2) vertical line from top of great
 
trochanter; (3) line joining anterior superior spine to top of
 
great trochanter.
 
 
 
Bubonocele, a variety of tumour in
 
the groin.
 
 
 
Buccinator, a trumpeter.
 
 
 
Bulla, a knob; a bubble.
 
 
 
Burdach, fasciculus of, fasciculus
 
cuneatus.
 
 
 
Burns, falciform process of (ligament
 
of Hey), superior cornu of saphenous opening.
 
 
 
Burns’ space, suprasternal space.
 
 
 
Bursa, a sac containing fluid.
 
 
 
Bursa omentalis, lesser sac.
 
 
 
Cacumen, tip, peak, or end.
 
 
 
Caecum, blind.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
GLOSSARY
 
 
 
 
 
1700
 
 
 
Caeruleus, dark blue.
 
 
 
Calamus, a reed-pen.
 
 
 
Calcaneum, the heel.
 
 
 
Calcar, a spur.
 
 
 
Calcination, reduction to a powder
 
(or line) by heat.
 
 
 
Calcis, of the heel.
 
 
 
Calix, a cup or goblet.
 
 
 
Callosal convolution, gyrus cinguli.
 
 
 
Calloso-marginal fissure, sulcus cinguli.
 
 
 
Callosum, hard, thick.
 
 
 
Calvaria ( calva , the bald scalp), the
 
upper part of the skull.
 
 
 
Canalis reuniens, ductus reuniens.
 
 
 
Cancellated, lattice-formed, reticulated.
 
 
 
Canthus, the angle of the eye.
 
 
 
Capillary, pertaining to the hair;
 
a vessel of hair-like minuteness.
 
 
 
Capitellum, a small head.
 
 
 
Capsular, suprarenal.
 
 
 
Caput gallinaginis, urethral crest.
 
 
 
Caput medusae, varicose veins radiating from umbilicus in portal
 
obstruction.
 
 
 
Cardia, the opening of the stomach;
 
the heart.
 
 
 
Cardiac, pertaining to the heart
 
(originally to the stomach).
 
 
 
Cardinal, principal or chief.
 
 
 
Carina, a keel.
 
 
 
Carneae, pertaining to flesh.
 
 
 
Carotid, stupefying; or perhaps from
 
two Greek words meaning ‘ head ’
 
and ‘ ear.’
 
 
 
Carpus, the wrist.
 
 
 
Cartilages, alar, lower lateral cartilage.
 
 
 
Cartilages, lateral, upper lateral cartilage (of nose).
 
 
 
Cartilages, Santorini, of, corniculate
 
cartilage.
 
 
 
Cartilages, Wrisberg, of, cuneiform
 
cartilage.
 
 
 
Caruncula, a little piece of flesh.
 
 
 
Caruncula sublingualis, sublingual
 
papilla.
 
 
 
Carunculae myrtiformes, carunculae
 
hymenales.
 
 
 
 
 
Cauda, a tail.
 
 
 
Caudate, tailed.
 
 
 
Caudate lobe (O.T.), tail of caudate
 
lobe.
 
 
 
Cavernous, full of hollows or cavities.
 
 
 
Centimetre (cm.), § of an English
 
inch.
 
 
 
Cephalic, pertaining to the head.
 
Cerato, horny.
 
 
 
Ceruminous, pertaining to wax.
 
Chiasma, two lines placed like an X.
 
Choana, a funnel.
 
 
 
Choanse, posterior apertures of nose.
 
Choledochus, bile-receiving.
 
Chondral, pertaining to cartilage.
 
 
 
Choroid (Chorioid), like skin.
 
Cinereus, ash-coloured.
 
 
 
Cingulum, a small girdle.
 
Circumflexus, bent around.
 
Circumvallate papillae, vallate papillae.
 
 
 
Cisterna, a cistern or reservoir.
 
Clarke, posterior vesicular column of,
 
 
 
thoracic (dorsal) nucleus.
 
Claustrum, a bulwark, barrier, or
 
inclosure.
 
 
 
Clava, a club; gracile tubercle.
 
Clavicle, from clavis, a key, or possibly a hoop-stick.
 
 
 
Cleido-, pertaining to the clavicle.
 
Clinoid, like the knob of a bedpost.
 
Clitoris, from a Greek verb meaning
 
‘ I shut up ’ or ‘ enclose.’
 
 
 
Clivus, a slope.
 
 
 
Cloaca, a sewer or drain.
 
 
 
Coccyx, a cuckoo.
 
 
 
Cochlea, a snail.
 
 
 
Cochlea, membranous, duct of cochlea.
 
 
 
Cochleariformis, spoon-like.
 
 
 
Coeliac, pertaining to the belly.
 
Colliculus, a little hill.
 
 
 
Colliculus, quadrigeminal body.
 
Colliculus seminalis, urethral crest.
 
Colon, the great gut.
 
 
 
Columns, rectal (Morgagni), anal
 
columns.
 
 
 
Comes, a companion.
 
 
 
Comma tract, semilunar tract.
 
 
 
 
 
 
 
 
 
 
 
 
 
GLOSSARY
 
 
 
 
 
Complexus, literally, folded together;
 
encompassing.
 
 
 
Concatenatae, chained together.
 
Concatenate glands, deep cervical
 
(lymph) glands.
 
 
 
Concha, a shell.
 
 
 
Condyle (‘ knuckle ’), a small round
 
prominence covered by cartilage.
 
Coni vasculosi, lobules of epididymis.
 
Conjunctiva, connecting.
 
Conniventes, winking or blinking.
 
Conoid, cone-like.
 
 
 
Conoid tubercle, coracoid tuberosity.
 
Conus arteriosus, infundibulum.
 
Conus elasticus, crico-vocal membrane.
 
 
 
Convoluta, rolled together.
 
 
 
Coracoid, like a crow or raven.
 
 
 
Cord, vocal, false, vestibular folds.
 
Cord, vocal, true, vocal fold.
 
Cordiform, heart-shaped.
 
 
 
Cords (gangliated, lumbo-sacral,
 
etc.), trunks.
 
 
 
Cornea, horny.
 
 
 
Corniculum, a little horn.
 
 
 
Cornu ammonis, hippocampus.
 
Coronal, literally, pertaining to a
 
crown; transverse.
 
 
 
Coronary, encircling.
 
 
 
Coronoid, like a crooked beak.
 
Corpora albicantia (brain), corpora
 
mamillaria.
 
 
 
Corpus (of long bone), shaft.
 
 
 
Corpus adiposum buccae, buccal pad.
 
Corpus arantii, nodule (aortic and
 
pulmonary valves).
 
 
 
Corpus cavernosum penis, corpus
 
cavernosum.
 
 
 
Corpus cavernosum urethrae, corpus
 
spongiosum.
 
 
 
Corrugator, a wrinkler.
 
 
 
Cortex, the bark or outer covering.
 
Costal, pertaining to a rib.
 
 
 
Cotyloid, cup-like.
 
 
 
Cowper’s gland, bulbo-urethral gland.
 
Coxa, the hip.
 
 
 
Cranium, the skull.
 
 
 
Crassum, thick, dense, or bulky.
 
Cremaster, a suspender.
 
 
 
Cribriform, sieve-like.
 
 
 
 
 
1701
 
 
 
Cribrosa, perforated with sieve-like
 
pores.
 
 
 
Cricoid, like a ring.
 
 
 
Crista tuberculi majoris, lateral lip
 
of bicipital groove.
 
 
 
Crista tuberculi minoris, medial lip
 
of bicipital groove.
 
 
 
Crucial, pertaining to, or shaped like,
 
a cross.
 
 
 
Crural, pertaining to the leg.
 
 
 
Crural canal, femoral canal.
 
 
 
Crural ring, femoral ring.
 
 
 
Crural septum, femoral septum.
 
 
 
Crus, cerebral peduncle.
 
 
 
Crusta, basis pedunculi.
 
 
 
Cryptorchismus, concealment of the
 
testis.
 
 
 
Cryptozygous, hidden arches.
 
 
 
Cubitum, the elbow.
 
 
 
Cucullaris, pertaining to a cowl or
 
hood.
 
 
 
Culmen, the top or summit.
 
 
 
Cuneate, wedge-shaped.
 
 
 
Cuneiform bone (hand), triquetrum.
 
 
 
Cuneus, a wedge.
 
 
 
Cupola, a dome.
 
 
 
Cymba, a boat or skiff.
 
 
 
Cystic, pertaining to the gall-bladder.
 
The condition of a thin-walled
 
swelling containing fluid or semifluid.
 
 
 
Cytoplasm, formative yolk; protoplasm in a cell.
 
 
 
Dacryon, a tear.
 
 
 
Dartos, skinned or flayed.
 
 
 
Deciduous, falling away.
 
 
 
Decussation of lemnisci (fillet), sensory decussation.
 
 
 
Deferens, carrying away.
 
 
 
Deiters, nucleus of, lateral vestibular
 
nucleus.
 
 
 
Dens, odontoid process.
 
 
 
Dens serotinus, wisdom tooth.
 
 
 
Dentate fascia, dentate gyrus.
 
 
 
Descemet’s membrane, posterior elastic lamina of cornea.
 
 
 
Detrusor, from detrudo, I drive away.
 
 
 
Deutoplasm, literally, wet plasm;
 
nutritive yolk.
 
 
 
 
 
 
 
 
 
 
 
 
 
1702
 
 
 
 
 
GLOSSARY
 
 
 
 
 
Dia-, through or between.
 
 
 
Diaphragm, a partition.
 
 
 
Diaphysis grow between ’), the
 
shaft of a bone, or the part which
 
grows between the epiphyses.
 
 
 
Diarthrosis, an ‘ apart ’ joint— i.e.,
 
a ‘ free ’ joint (the articular surfaces being free to play upon each
 
other); synovial joint.
 
 
 
Diencephalon, the ’tween-brain or
 
inter-brain; thalamencephalon.
 
 
 
Digastric, having two bellies.
 
 
 
Diploe, a doubling.
 
 
 
Discus proligerus, cumulus ovaricus.
 
 
 
Diverticulum, from diverto, ‘ I separate/ or ‘ part/ or ‘ go a different
 
way.’
 
 
 
Dolichocephalic, long-headed.
 
 
 
Dorsal, pertaining to the back
 
aspect.
 
 
 
Dorsum, the back.
 
 
 
Douglas, pouch of, recto-uterine or
 
recto-vaginal pouch.
 
 
 
Douglas, semilunar fold of, arcuate
 
line.
 
 
 
Duct, nasal, naso-lacrimal duct.
 
 
 
Ductus deferens, vas deferens.
 
 
 
Ductus perilymphaticus, aqueduct of
 
cochlea.
 
 
 
Duodenum, twelve (probably fingerbreadths) .
 
 
 
Ebur, -oris, ivory.
 
 
 
Eburnea, pertaining to ivory.
 
 
 
Ectopia, a displacement.
 
 
 
Efferent, carrying out.
 
 
 
Embolif ormis, beak-shaped or wedgeshaped.
 
 
 
Emissary, sent out.
 
 
 
Emulgent, milking, straining out.
 
 
 
Enarthrosis, ball-and-socket joint.
 
 
 
Encephalon, the contents of the head
 
or skull.
 
 
 
Endocardium, ‘ within the heart ’;
 
the lining membrane of the cardiac
 
chambers.
 
 
 
Endognathion, literally, inner jaw.
 
 
 
Endosteum, ‘ within a bone ’; the
 
medullary membrane.
 
 
 
Ensiform, sword-like.
 
 
 
 
 
Ensiform process, xiphoid process.
 
 
 
Entomion, a notch.
 
 
 
Ependyma, from Greek words meaning ' clothing upon/
 
 
 
Ephippium, a saddle.
 
 
 
Epi-, upon or over, above.
 
 
 
Epicardium, upon the heart.
 
 
 
Epididymis, upon the testicle.
 
 
 
Epiglottis, cushion of, tubercle of
 
epiglottis.
 
 
 
Epiotic, upon or over the ear.
 
 
 
Epiphysis (‘ grow upon ’); a process
 
of a bone which has a secondary
 
centre of ossification.
 
 
 
Epiploon, from a Greek verb meaning
 
‘ to float upon/
 
 
 
Epipteric, upon a wing.
 
 
 
Epipteric bone, sutural bone at
 
pterion.
 
 
 
Epistropheus, axis.
 
 
 
Epoophoron, above the egg-bearing
 
organ.
 
 
 
Erythroblast, red (cell) germ.
 
 
 
Ethmoid, like a strainer.
 
 
 
Eustachian cushion, tubal elevation.
 
 
 
Eustachian spine (of medial pterygoid plate), processus tubarius.
 
 
 
Eustachian tube, pharyngo-tympanic
 
tube.
 
 
 
Eustachian valve, valve of inferior
 
 
 
vena cava.
 
 
 
Exognathion, literally, outer jaw.
 
 
 
Exomphalos, out of the navel.
 
 
 
Facet (French, facette, a little face),
 
a small plane surface, usually
 
articular.
 
 
 
Falciform, sickle-like.
 
 
 
Fallopian tube, uterine tube.
 
 
 
Falx, a sickle.
 
 
 
Falx aponeurotica inguinalis, conjoint tendon.
 
 
 
Fascia, a bandage, or a bundle of
 
reeds.
 
 
 
Fascia bulbi, fascial sheath of eyeball.
 
 
 
Fascia, Camper’s, superficial layer of
 
superficial fascia of anterior abdominal wall.
 
 
 
Fascia, Colies’, deep layer of superficial fascia of perineum.
 
 
 
 
 
 
 
 
 
/
 
 
 
 
 
 
 
 
 
GLOSSARY
 
 
 
 
 
1703
 
 
 
 
 
Fascia, coraco-clavicular, clavi-pec
 
toral fascia.
 
 
 
Fascia infundibular, internal spermatic fascia.
 
 
 
Fascia intercolumnar, external spermatic fascia.
 
 
 
Fascia, Scarpa’s, deep layer of superficial fascia of anterior abdominal
 
wall.
 
 
 
Fascia, Sibson’s, suprapleural membrane.
 
 
 
Fasciculus, a small bundle.
 
 
 
Fasciola cinerea, splenial gyrus.
 
 
 
Fastigium, a roof.
 
 
 
Fauces, the throat.
 
 
 
Fauces, anterior pillar, glosso-palatine arch.
 
 
 
Fauces, posterior pillar, pharyngopalatine arch.
 
 
 
Fel, the gall-bladder.
 
 
 
Femur, the thigh.
 
 
 
Fenestra, an opening, a window.
 
 
 
Fenestra ovalis, fenestra vestibuli.
 
 
 
Fenestra rotunda, fenestra cochleae.
 
 
 
Ferruginea, pertaining to iron-rust.
 
 
 
Fibula, a buckle, clasp, or brace.
 
 
 
Fillet, lemniscus.
 
 
 
Filum, a thread.
 
 
 
Fimbria, a fringe.
 
 
 
Fimbriatum, fringed.
 
 
 
Fissure, a cleft or slit.
 
 
 
Fistula, .a pipe or tube.
 
 
 
Flechsig, tract of, posterior spinocerebellar tract.
 
 
 
Flocculus, a little lock of wool.
 
 
 
Fold, bloodless (Treves), ileo-caecal
 
fold.
 
 
 
Fold, ileo-colic, vascular fold of
 
caecum.
 
 
 
Fold, recto-vesical, sacro-genital fold.
 
 
 
Follicle, a small bag or sac.
 
 
 
Fontana, spaces of, spaces of iridocorneal angle.
 
 
 
Fontanelle, a small spring.
 
 
 
Foramen, an aperture or a hole.
 
 
 
Forceps, a claw of a beetle.
 
 
 
Fornicatus, pertaining to an arch.
 
 
 
Fornix, an arch or a vault.
 
 
 
Fossa, a ditch or trench.
 
 
 
Fossa, antecubital, cubital.
 
 
 
 
 
Fossa ovalis, saphenous opening.
 
 
 
Fossa, rhomboid, floor of fourth
 
ventricle.
 
 
 
Fossa, spheno-maxillary, pterygopalatine fossa.
 
 
 
Fourchette, a fork.
 
 
 
Fovea, a small pit.
 
 
 
Foveola, a very small pit.
 
 
 
Frenulum, a small bridle.
 
 
 
Frenum, a bridle.
 
 
 
Frontal, pertaining to the forehead.
 
 
 
Frontal spine (of frontal), nasal spine.
 
 
 
Fundiform, sling-like.
 
 
 
Funicular, pertaining to a cord.
 
 
 
Funiculus, a slender rope, a cord.
 
 
 
Furcalis, pertaining to a two-pronged
 
fork.
 
 
 
Furcula, a small two-pronged fork.
 
 
 
Fusca, dark or dusky.
 
 
 
Galactophorous, milk-carrying.
 
 
 
Galea, a helmet.
 
 
 
Galea aponeurotica, epicranial aponeurosis.
 
 
 
Galen, great vein of, great cerebral
 
vein.
 
 
 
Galen, veins of, internal cerebral
 
veins.
 
 
 
Gallinaginis, of a woodcock.
 
 
 
Gallus, a cock.
 
 
 
Ganglion, a swelling or excrescence.
 
 
 
Ganglion, aortico-renal, lower part
 
of coeliac ganglion.
 
 
 
Ganglion, Gasserian, trigeminal ganglion.
 
 
 
Ganglion, jugular (O.T.), superior
 
ganglion of ninth.
 
 
 
Ganglion, jugular (B.N.A.), superior
 
ganglion of tenth.
 
 
 
Ganglion, lenticular, ciliary ganglion.
 
 
 
Ganglion, Meckel’s, spheno-palatine
 
ganglion.
 
 
 
Ganglion nodosum (B.N.A.), inferior ganglion of tenth.
 
 
 
Ganglion, ophthalmic, ciliary ganglion.
 
 
 
Ganglion, petrous (O.T. and B.N.A.),
 
 
 
inferior ganglion of ninth.
 
 
 
Ganglion, semilunar, trigeminal ganglion.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1704
 
 
 
 
 
GLOSSARY
 
 
 
 
 
Ganglion, stellate, first thoracic
 
ganglion.
 
 
 
Ganglion, submaxillary, submandibular ganglion.
 
 
 
Gartner’s duct, duct of epoophoron.
 
Gastric, pertaining to the stomach.
 
 
 
Gastrocnemius, the belly of the
 
leg.
 
 
 
Gemellus, paired or double.
 
 
 
Geminus, twin or twofold.
 
 
 
Geniculate, knee-like.
 
 
 
Genio-, pertaining to the chin.
 
Gennari, stria of, visual stria.
 
 
 
Genu, the knee.
 
 
 
Gerota’s capsule, renal fascia.
 
Giacomini, banderella or frenulum,
 
tail of dentate gyrus.
 
 
 
Gimbernat’s ligament, pectineal part
 
of inguinal ligament.
 
 
 
Ginglymus, a hinge.
 
 
 
Ginglymus, hinge-joint.
 
 
 
Giraldes, organ of, paradidymis.
 
Glabella, without hair; smooth.
 
Gladiolus, a small sword.
 
 
 
Gladiolus, body of sternum.
 
 
 
Gland, Bartholin’s, greater vestibular
 
gland.
 
 
 
Gland, Cowper’s, bulbo-urethral
 
gland.
 
 
 
Glenoid, like a shallow socket.
 
Glisson’s capsule, hepato-biliary capsule.
 
 
 
Globosus, round or spherical.
 
Globus, a globe or sphere.
 
Glomerulus, a small ball of thread.
 
Glosso-, pertaining to the tongue.
 
Glottis, the mouthpiece of a flute.
 
Gluteal, pertaining to the buttock.
 
 
 
Gnathic, pertaining to the jaw.
 
Gnathion, the jaw.
 
 
 
Gomphosis, a bolting together.
 
Gonion, an angle.
 
 
 
Gracilis, slender.
 
 
 
Grisea, grey.
 
 
 
Gubernaculum, a rudder.
 
 
 
Gula, the gullet.
 
 
 
Gustatory, pertaining to taste.
 
Guttural, pertaining to the throat.
 
Gyrus, a circle; a crook.
 
 
 
 
 
Habenula, a small thong or rein.
 
Hsemorrhoidal, associated with
 
haemorrhoids.
 
 
 
Hallux, the great toe.
 
 
 
Ham, a thing bent or crooked.
 
Hamular, hook-shaped.
 
 
 
Harmonia, a fitting together.
 
Hartmann’s pouch, sacculation at
 
junction of neck and body of gallbladder.
 
 
 
Hassall, corpuscles of (thymus), concentric corpuscles.
 
 
 
Haustrum, a machine for drawing
 
water.
 
 
 
Heister’s valves, spiral valve.
 
Helicine, spiral.
 
 
 
Helicotrema, hole of a spiral.
 
 
 
Helix, a coil or spiral.
 
 
 
Hepar, the liver.
 
 
 
Hepatic, pertaining to the liver.
 
Hernia, a sprout; a rupture.
 
Hesselbach’s triangle, inguinal triangle.
 
 
 
Hiatus, a gap.
 
 
 
Hiatus Fallopii, hiatus for superficial
 
petrosal nerve.
 
 
 
Highmore, antrum of, maxillary
 
sinus.
 
 
 
Hilum, a little thing; a trifle.
 
 
 
Hippocampus, a seahorse.
 
Hippocampus major, hippocampus.
 
Hippocampus minor, calcar avis.
 
Hircina, pertaining to a goat.
 
 
 
His, bundle of, atrio-ventricular
 
bundle.
 
 
 
Homodynamic]
 
 
 
Homogenesis see Chapter I.
 
Homologous )
 
 
 
Houston’s valves, horizontal folds of
 
rectum.
 
 
 
Huguier, canal of, anterior canaliculus for chorda tympani.
 
 
 
Humerus, the upper part of the arm;
 
the shoulder.
 
 
 
Hunter’s canal, subsartorial canal.
 
Hyaline, glassv.
 
 
 
Hyaloid, like glass.
 
 
 
Hydatid, a watery vesicle.
 
 
 
Hydrocele, a watery tumour.
 
 
 
Hymen, the marriage deity.
 
 
 
 
 
/
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
GLOSSARY
 
 
 
 
 
1705
 
 
 
 
 
Hyoid, like the Greek letter upsilon.
 
 
 
Hypo-, beneath or under.
 
 
 
Hypophysis, ‘ grow beneath.’
 
 
 
Hypothenar, beneath the palm of the
 
hand.
 
 
 
Ileum, implying twists or coils.
 
 
 
Ilium, literally of the soft parts—
 
i.e., of the flank; os ilium, the bone
 
of the flank.
 
 
 
Ima, lowest.
 
 
 
Impar, dissimilar (in number), unequal.
 
 
 
Incisivus, cutting into.
 
 
 
Incisura jugularis, suprasternal notch.
 
 
 
Incisura scapularis, suprascapular
 
notch.
 
 
 
Incisura semilunaris (ulna), trochlear
 
notch.
 
 
 
Infundibuliform, funnel-shaped.
 
 
 
Infundibulum, a funnel.
 
 
 
Inguinal, pertaining to the groin.
 
 
 
Inion, literally, the occiput.
 
 
 
Innominatum, unnamed.
 
 
 
Insula, an island.
 
 
 
Intercalary, inserted.
 
 
 
Internodium, the space between two
 
knots or joints.
 
 
 
Interparietal bone, membranous part
 
of occipital as a separate bone.
 
 
 
Interpositum, placed between.
 
 
 
Interstitial, belonging to interstices
 
or small parts between the main
 
parts of bodies.
 
 
 
Intertubercular sulcus, bicipital
 
groove.
 
 
 
Intumescentia, enlargement (spinal
 
cord).
 
 
 
Iris, the rainbow.
 
 
 
Ischiatic, pertaining to the hip.
 
 
 
Ischium, the hip.
 
 
 
Isthmus, faucium, oro-pharyngeal
 
isthmus.
 
 
 
Isthmus rhombencephali, upper constricted end of fourth ventricle.
 
 
 
Iter, a passage or road.
 
 
 
Jacobson, cartilage of, sub-vomerine
 
cartilage.
 
 
 
Jacobson, organ of, vomero-nasal
 
organ.
 
 
 
 
 
Jacobson’s nerve, tympanic nerve.
 
 
 
Jejunum, empty or hungry.
 
 
 
Jugal, yolking.
 
 
 
Jugular, pertaining to the throat.
 
 
 
Jugular notch (B.N.A.), suprasternal
 
notch.
 
 
 
Jugum, a yolk.
 
 
 
Kerckring, ossicle, occasional centre
 
in posterior margin of foramen
 
magnum.
 
 
 
Key and Retzius, foramina of
 
 
 
(Luschka), lateral apertures of
 
fourth ventricle.
 
 
 
Kobelt’s tubes, epoophoron.
 
 
 
Labbe, vein of, inferior anastomotic
 
vein (connects superficial middle
 
cerebral with transverse sinus).
 
 
 
Labrum, a basin.
 
 
 
Lacertus fibrosus, bicipital aponeurosis.
 
 
 
Laciniosum, full of folds, indented,
 
jagged.
 
 
 
Lacrimal, pertaining to tears.
 
 
 
Lacteal, pertaining to milk.
 
 
 
Lactiferous, milk-carrying.
 
 
 
Lacuna, a hollow or cavity.
 
 
 
Lacunee (of sagittal sinus), lacunae
 
laterales.
 
 
 
Lacunar, pertaining to a hollow or
 
gap.
 
 
 
Lacunar ligament, pectineal part of
 
inguinal ligament.
 
 
 
Lamella, a small plate.
 
 
 
Lamina, a plate.
 
 
 
Lamina cinerea, lamina terminalis.
 
 
 
Lamina cribrosa, medial boundary
 
of internal auditory meatus.
 
 
 
Lamina papyracea, orbital plate of
 
ethmoid.
 
 
 
Lamina quadrigemina, tectum.
 
 
 
Lateral, on the side of. Used in
 
reference to the sagittal plane of
 
the body.
 
 
 
Lateral mass (ethmoid), labyrinth.
 
 
 
Lateral sinus, transverse sinus.
 
 
 
Latissimus, broadest.
 
 
 
Latum, broad.
 
 
 
Lemniscus, a ribbon.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1706
 
 
 
 
 
GLOSSARY
 
 
 
 
 
Leptorhine, having small narrow
 
nostrils.
 
 
 
Levator, a lifter or raiser.
 
 
 
Lien, the spleen.
 
 
 
Lieno-, pertaining to the spleen.
 
Ligament, a band or bandage.
 
 
 
Ligula, a little tongue.
 
 
 
Limbic lobe, gyrus fornicatus.
 
Limbous, pertaining to a border.
 
Limbus, a border.
 
 
 
Limbus fossae ovalis (or limbus
 
ovalis), annulus ovalis.
 
 
 
Limen, a threshold.
 
 
 
Linea, a line.
 
 
 
Lines, oblique (tibia), soleal line.
 
Lines, oblique internal (jaw), mylohyoid line.
 
 
 
Lines (occiput), nuchal lines.
 
 
 
Lines, popliteal, soleal line.
 
 
 
Lingual, pertaining to the tongue.
 
Lingula, a little tongue.
 
 
 
Lister’s tubercle, dorsal tubercle of
 
radius.
 
 
 
Longissimus, longest.
 
 
 
Longitudinal sinus, sagittal sinus.
 
Lower, tubercle of, intervenous
 
tubercle (heart).
 
 
 
Lumbar, pertaining to the loin.
 
Lumbricalis, like an earth-worm.
 
Lunar, pertaining to the moon.
 
Lunula, a little moon; a crescent.
 
Luteum, of a yellow colour.
 
 
 
Luys’ nucleus, subthalamic body.
 
Lymphatic, from lympha, pure or
 
spring water; lymph.
 
 
 
Lyra, a lyre; hippocampal commissure.
 
 
 
McBurney’s point (base of appendix),
 
 
 
junction of lower and middle
 
thirds of spino-umbilical line.
 
Macula, a spot.
 
 
 
Magendie, foramen, median aperture
 
of fourth ventricle.
 
 
 
Magnum, os, capitate bone.
 
 
 
Malar, pertaining to the cheek.
 
 
 
Malar bone, zygomatic bone.
 
Malleolus, a small hammer or mallet.
 
 
 
Malleus, a hammer or mallet.
 
 
 
 
 
Mamma, a breast or pap.
 
 
 
Mammilla, a little breast or pap.
 
Properly spelt mamilla.
 
 
 
Mandible, the chewing bone— i.e.,
 
lower jaw.
 
 
 
Manubrium, a handle or hilt.
 
 
 
Marshall, oblique vein, oblique vein
 
of left atrium.
 
 
 
Massa intermedia, interthalamic
 
 
 
connexus.
 
 
 
Masseter, the chewing muscle.
 
 
 
Mastoid, breast- or pap-like (nipplelike).
 
 
 
Maxilla, jaw.
 
 
 
Meatus (pi. Meatfis), a passage or
 
canal.
 
 
 
Meckel’s cave, cavum trigeminale.
 
 
 
Meckel’s diverticulum, diverticulum
 
ilei.
 
 
 
Mediastinum, standing in the middle;
 
a partition.
 
 
 
Medulla, marrow.
 
 
 
Megacephalic, having a large head.
 
 
 
Megaseme, having a large index.
 
 
 
Meibomian glands, tarsal glands.
 
 
 
Meissner’s plexus, plexus of the submucosa.
 
 
 
Membrane, costo-coracoid, clavi
 
pectoral fascia.
 
 
 
Meninges, membranes.
 
 
 
Meniscus, a crescent.
 
 
 
Meniscus (knee), semilunar cartilage.
 
 
 
Mental, pertaining to the chin.
 
 
 
Mesaticephalic, having a head with
 
an index of mean value.
 
 
 
Mesencephalon, the mid-brain.
 
 
 
Mesentery, in the middle of, or
 
among, the intestines.
 
 
 
Mesial, nearer to the sagittal plane
 
of the body.
 
 
 
Meso-, in the midst of. In compounds usually implies a structure
 
like a mesentery, a peritoneal attachment fold.
 
 
 
Mesocephalic, pertaining to a head
 
of mean capacity.
 
 
 
Mesogastrium=meso- (q.v.) and
 
stomach.
 
 
 
Mesognathion, middle jaw.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
GLOSSARY
 
 
 
 
 
Mesometrium=meso- [q-v.) and
 
womb.
 
 
 
Mesonephros, mid-kidney.
 
 
 
Mesorhine, pertaining to an intermediate nasal index; a condition
 
intermediate between broad-nosed
 
and narrow-nosed.
 
 
 
Mesosalpinx =meso- (q.v.) and tube.
 
 
 
Mesoseme, intermediate index.
 
 
 
Meta-, after or beyond.
 
 
 
Meta-nephros, hind-kidney.
 
 
 
Metencephalon, the after-brain.
 
 
 
Metopic, pertaining to the forehead.
 
 
 
Metopism, persistence of the metopic
 
or frontal suture.
 
 
 
Microcephalic, pertaining to a small
 
head.
 
 
 
Microseme, small index.
 
 
 
Middle commissure, interthalamic
 
connexus.
 
 
 
Millimetre (mm.), slightly less than
 
2V of an English inch.
 
 
 
Minimae, least, smallest.
 
 
 
Mitral, resembling an Asiatic headdress, or mitre.
 
 
 
Modiolus, the nave of a wheel.
 
 
 
Molar, pertaining to a mill, or to
 
grinding.
 
 
 
Monro, foramen, interventricular
 
foramen.
 
 
 
Mons veneris, mons pubis.
 
 
 
Montanum, pertaining to a mountain.
 
 
 
Monticulus, a small mountain.
 
 
 
Morbus, a disease.
 
 
 
Muliebris, pertaining to a woman,
 
feminine.
 
 
 
Miillerian duct, para-mesonephric
 
duct.
 
 
 
Multangulum majus, os, trapezium.
 
 
 
Multifidus, many cleft; divided into
 
many parts.
 
 
 
Musculo-spiral nerve, radial nerve.
 
 
 
Myelencephalon, marrow-brain.
 
 
 
Myeloplaxes, marrow-plates.
 
 
 
Myentericus, pertaining to the muscular tissue of the bowel.
 
 
 
Mylo-, pertaining to a mill.
 
 
 
Myocardium, the muscular tissue of
 
the heart.
 
 
 
Myrtiform, like a myrtle-berry.
 
 
 
 
 
1707
 
 
 
Nares, posterior, posterior apertures
 
of nose.
 
 
 
Naris (pi. nares), a nostril.
 
 
 
Nasal, pertaining to the nose.
 
 
 
Natal, pertaining to the buttock.
 
Natis (pi. nates), the buttock.
 
Navicular, pertaining to a boat.
 
Nephros, a kidney.
 
 
 
Neural, pertaining to a nerve.
 
Neuroglia, literally ‘ nerve glue.’
 
Nictitans, winking.
 
 
 
Norma, a rule or measure (aspect).
 
Notochord, string or cord of the back.
 
Nucha, the nape of the neck.
 
 
 
Nuck, canal, vaginal process.
 
Nucleus, a kernel.
 
 
 
Nuhn, glands, anterior lingual (seromucous) glands.
 
 
 
Nymphae, nymphs or goddesses of
 
the fountains, woods, trees, etc.;
 
labia minora.
 
 
 
Obelion, a horizontal line (perhaps
 
a little spit).
 
 
 
Obex, a bolt; a barrier.
 
 
 
Obturator, one who closes or stops
 
up.
 
 
 
Occipital, pertaining to the back
 
part of the head.
 
 
 
Odontoblast, a tooth-germ.
 
 
 
Odontoid, tooth-like.
 
 
 
Odoriferae, carrying odours.
 
(Esophagus, food-carrier.
 
 
 
Olecranon, head or point of the
 
forearm.
 
 
 
Olfactory, pertaining to smell.
 
Olfactory trigone, olfactory pyramid.
 
Olivary, pertaining to an olive.
 
Omentum, that which is drawn over.
 
 
 
Omentum, gastro - hepatic, lesser
 
omentum.
 
 
 
Omentum, gastro-splenic, gastrosplenic ligament.
 
 
 
Omo-, pertaining to the shoulder.
 
Omphalo-, pertaining to the navel.
 
Operculum, a cover or lid.
 
 
 
Ophryon, the eyebrow.
 
 
 
Ophthalmic, pertaining to the eye.
 
Opisthion, hinder or rear.
 
 
 
Opisthotic, behind the ear.
 
 
 
 
 
 
 
 
 
1708
 
 
 
 
 
GLOSSARY
 
 
 
 
 
Optic, pertaining to sight.
 
 
 
Optic thalamus, thalamus.
 
 
 
Ora, a border or margin.
 
Orthognathous pertaining to a
 
straight (non-projecting) jaw.
 
 
 
Os incae, interparietal bone.
 
 
 
Os japonicum, bi-partite zygomatic
 
bone.
 
 
 
Os magnum, capitate bone.
 
 
 
Os, oris, a mouth.
 
 
 
Os, ossis, a bone.
 
 
 
Os tincae, external os of uterus.
 
Ossicle of Kerckring, occasional
 
centre in posterior margin of