The Accessory Organs of the Eye

EYES

=1c. 3. The Accessory Organs of the Eye (Organa Oculi Accessoria)= =The Ocular Muscles (musculi oculi)= http://www.bartleby.com/107/Images/large/image888.gif http://www.bartleby.com/107/Images/large/image889.gif http://info.med.yale.edu/caim/cnerves/cn6/cn6_graphics/cn6_4.jpg http://www.nature.com/eye/journal/v20/n10/images/6702376f10.jpg
 * The accessory organs of the eye include the ocular muscles, the fasciae, the eyebrows, the eyelids, the conjunctiva, and the lacrimal apparatus.
 * The ocular muscles are :
 * Levator palpebrae superioris
 * Rectus medialis
 * Rectus superior
 * Rectus lateralis
 * Rectus inferior
 * Obliquus superior
 * Obliquus inferior
 * FIG. 888– Sagittal section of right orbital cavity. (See enlarged image)
 * FIG. 889– Muscles of the right orbit. (See enlarged image)


 *  Superior rectus is innervated by Superior branch of oculomotor nerve
 *  Superior rectus has origin in Annulus of Zinn
 *  Superior rectus has insertio in the eye ball (anterior, superior surface)
 *  Superior rectus has function Elevation, 	Intorsion,	Adduction[1]
 *  Inferior rectus is innervated by Inferior branch of oculomotor nerve
 *  Inferior rectus has origo in Annulus of Zinn
 *  Inferior rectus has insertio in the	eye ball(anterior, inferior surface)
 *  Inferior rectus has function Depression	Extorsion	Adduction[1]
 *  Lateral rectus is innervated by Abducens nerve
 *  Lateral rectus has origo in Annulus of Zinn
 *  Lateral rectus has insertio in the	eye ball(anterior, lateral surface)
 *  Lateral rectus has function Abduction
 *  Medial rectus is innervated by Inferior branch of oculomotor nerve
 *  Medial rectus has origo in Annulus of Zinn
 *  Medial rectus has insertio in the	eye ball(anterior, medial surface)
 *  Medial rectus has function Adduction
 *  Superior oblique is innervated by Trochlear nerve
 *  Superior oblique has origo in Annulus of Zinnvia the Trochlea of superior oblique
 *  Superior oblique has insertio in the	eye ball(posterior, superior, lateral surface)
 *  Superior oblique has function Intorsion	Depression	Abduction
 *  Inferior oblique is innervated by Inferior branch of oculomotor nerve
 *  Inferior oblique has origo in Maxillary bone
 *  Inferior oblique has insertio in the	eye ball(posterior, superior, lateral surface)
 *  Inferior oblique has function Intorsion	Depression	Extorsion	Elevation	Abduction[1]
 *  Levator palpebrae superioris is innervated by Oculomotor nerve
 *  Levator palpebrae superioris has origo in Sphenoid bone
 *  Levator palpebrae superioris has insertio in tarsal plate of upper eyelid
 *  Levator palpebrae superioris has function Retracts & elevates eyelid

The Levator palpebrae superioris

 * Levator palpebrae superioris is thin, flat, and triangular in shape.
 * Levator palpebrae superioris arises from the under surface of the small wing of the sphenoid bone, above
 * Levator palpebrae superioris arises in front of the optic foramen,
 * Levator palpebrae superioris is separated from optic foramen by the origin of the Rectus superior.
 * Levator palpebrae superioris is narrow and tendinous At its origin.
 * Levator palpebrae superioris becomes broad and fleshy in the middle
 * Levator palpebrae superioris ends anteriorly in a wide aponeurosis which splits into three lamellae.
 * The superficial lamella of Levator palpebrae superioris blends with the upper part of the orbital septum,
 * The superficial lamella of Levator palpebrae superioris is prolonged forward above the superior tarsus to the palpebral part of the Orbicularis oculi, and to the deep surface of the skin of the upper eyelid.
 * The middle lamella of Levator palpebrae superioris is inserted into the upper margin of the superior tarsus,
 * The middle lamella of Levator palpebrae superioris is largely made up of non-striped muscular fibers,
 * The deepest lamella of Levator palpebrae superioris blends with an expansion from the sheath of the Rectus superior
 * The deepest lamella of Levator palpebrae superioris is attached to the superior fornix of the conjunctiva.
 * the upper part of the sheath of the Levator palpebrae becomes thickened in front
 * the upper part of the sheath of the Levator palpebrae forms a transverse ligamentous band which is attached to the sides of the orbital cavity above the anterior part of the muscle.
 * On the medial side, the upper part of the sheath of the Levator palpebrae is mainly fixed to the pulley of the Obliquus superior,
 * Some fibers of the upper part of the sheath of the Levator palpebrae are attached to the bone behind the pulley and a slip passes forward and bridges over the supraorbital notch;
 * on the lateral side,  the upper part of the sheath of the Levator palpebrae is fixed to the capsule of the lacrimal gland and to the frontal bone.
 * In front of the transverse ligamentous band, the sheath of the Levator palpebrae is continued over the aponeurosis of the Levator palpebrae, as a thin connective-tissue layer which is fixed to the upper orbital margin immediatly behind the attachment of the orbital septum.
 * When the Levator palpebrae contracts, the lateral and medial parts of the ligamentous band are stretched and check the action of the muscle; the retraction of the upper eyelid is checked also by the orbital septum coming into contact with the transverse part of the ligamentous band.	  4

The four Recti (Fig. 889)

 * All Rectus muscles arise from the annulus tendineus communis.
 * annulus tendineus communis is a fibrous ring
 * annulus tendineus communis surrounds the upper, medial, and lower margins of the optic foramen and encircles the optic nerve (Fig. 890).
 * annulus tendineus communis is completed by a tendinous bridge prolonged over the lower and medial part of the superior orbital fissure and attached to a tubercle on the margin of the great wing of the sphenoid, bounding the fissure.
 * The lower part of annulus tendineus communis is made of the tendon of Zinn
 * the tendon of Zinn gives origin to the Rectus inferior,+ part of the Rectus internus + the lower head of origin of the Rectus lateralis;
 * The upper part of annulus tendineus communis,is termed superior tendon of Lockwood
 * superior tendon of Lockwood gives origin to the Rectus superior, the rest of the Rectus medialis, and the upper head of the Rectus lateralis.
 * Each muscle passes forward to be inserted by a tendinous expansion into the sclera,
 * The Recti muscles are inserted at about 6 mm. from the margin of the cornea.
 * Between the two heads of the Rectus lateralis pass the two divisions of the oculomotor nerve, the nasociliary nerve, the abducent nerve, and the ophthalmic vein'''.
 * The Rectus medialis is the broadest of the four recti.
 *  the Rectus lateralis is the longest of the four recti.
 *  the Rectus superior is the thinnest and narrowest.

The Obliquus oculi superior (superior oblique)

 * The Obliquus oculi superior is a fusiform muscle,
 * The Obliquus oculi superior is placed at the upper and medial side of the orbit.
 * The Obliquus oculi superior arises immediately above the margin of the optic foramen
 * The Obliquus oculi superior arises above and medial to the origin of the Rectus superior
 * The Obliquus oculi superior, ends in a rounded tendon.
 * Rounded tendon of the superior obliqe moves soothly in a fibrocartilaginous ring attached to the trochlear fovea of the frontal bone.
 * Rounded tendon of the superior obliqe is reflected backward, lateralward, and downward beneath the Rectus superior to the lateral part of the bulb of the eye, and is inserted into the sclera, behind the equator of the eyeball,
 * the insertion of The Obliquus oculi superior lies between the Rectus superior and Rectus lateralis.	  6

The Obliquus oculi inferior (inferior oblique)

 * The Obliquus oculi inferior is a thin, narrow muscle,
 * The Obliquus oculi inferior is placed near the anterior margin of the floor of the orbit.
 * The Obliquus oculi inferior arises from the orbital surface of the maxilla, lateral to the lacrimal groove.
 * The Obliquus oculi inferior Passes lateralward, backward, and upward,
 * The Obliquus oculi inferior passes at first between the Rectus inferior and the floor of the orbit, and then between the bulb of the eye and the Rectus lateralis,
 * The Obliquus oculi inferior is inserted into the lateral part of the sclera between the Rectus superior and Rectus lateralis, near to, but somewhat behind the insertion of the Obliquus superior.

FIG. 890– Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure. (See enlarged image)

Nerves

 * The Levator palpebræ superiorisare supplied by the oculomotor nerve
 * Obliquus inferiorare supplied by the oculomotor nerve
 * the Recti superiorare supplied by the oculomotor nerve
 * rectus inferiorare supplied by the oculomotor nerve
 * rectus medialis are supplied by the oculomotor nerve;
 * the Obliquus superior is by the trochlear nerve;
 * the Rectus lateralis is supplied by the abducent nerve

Actions

 * The Levator palpebræ raises the upper eyelid,
 * The Levator palpebræ is the direct antagonist of the Orbicularis oculi.
 * The four Recti are attached to the bulb of the eye in such a manner that, acting singly, they will turn its corneal surface either upward, downward, medialward, or lateralward, as expressed by their names.
 * The movement produced by the Rectus superior or Rectus inferior is not quite a simple one, for inasmuch as each passes obliquely lateralward and forward to the bulb of the eye, the elevation or depression of the cornea is accompanied by a certain deviation medialward, with a slight amount of rotation.
 * These latter movements are corrected by the Obliqui, the Obliquus inferior correcting the medial deviation caused by the Rectus superior and the Obliquus superior that caused by the Rectus inferior. The contraction of the Rectus lateralis or Rectus medialis, on the other hand, produces a purely horizontal movement.
 * If any two neighboring Recti of one eye act together they carry the globe of the eye in the diagonal of these directions, viz., upward and medialward, upward and lateralward, downward and medialward, or downward and lateralward. Sometimes the corresponding Recti of the two eyes act in unison, and at other times the opposite Recti act together.
 * Thus, in turning the eyes to the right, the Rectus lateralis of the right eye will act in unison with the Rectus medialis of the left eye; but if both eyes are directed to an object in the middle line at a short distance, the two Recti mediales will act in unison. The movement of circumduction, as in looking around a room, is performed by the successive actions of the four Recti.
 * The Obliqui rotate the eyeball on its antero-posterior axis, the superior directing the cornea downward and lateralward, and the inferior directing it upward and lateralward; these movements are required for the correct viewing of an object when the head is moved laterally, as from shoulder to shoulder, in order that the picture may fall in all respects on the same part of the retina of either eye.	  9
 * A layer of non-striped muscle, the Orbitalis muscle of H. Müller, may be seen bridging across the inferior orbital fissure.	  10

Fascia
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 * FIG. 891– The right eye in sagittal section, showing the fascia bulbi (semidiagrammatic). (Testut.) (See enlarged image)
 * The Fascia Bulb is ALA capsule of Ténon (Fig. 891)
 * The Fascia Bulbis a thin membrane which envelops the bulb of the eye from the optic nerve to the ciliary region,
 * The Fascia Bulbseparates the bulb of the eye from the orbital fat and forming a socket in which the bulb of the eye plays.
 * The Fascia Bulb 's inner surface is smooth,
 * The Fascia Bulb 's inner surface is separated from the outer surface of the sclera by the periscleral lymph space.
 * the periscleral lymph space is continuous with the subdural and subarachnoid cavities,
 * the periscleral lymph space is traversed by delicate bands of connective tissue which extend between the fascia and the sclera.
 * The Fascia Bulb is perforated behind by the ciliary vessels and nerves,
 * The Fascia Bulb fuses with the sheath of the optic nerve and with the sclera around the entrance of the optic nerve.
 * In front The Fascia Bulb blends with the ocular conjunctiva, and
 * The Fascia Bulb with the ocular conjunctiva is attached to the ciliary region of the eyeball. * The Fascia Bulb is perforated by the tendons of the ocular muscles, and is reflected backward on each as a tubular sheath.
 * The sheath of the Obliquus superior is carried as far as the fibrous pulley of that muscle; that on the Obliquus inferior reaches as far as the floor of the orbit, to which it gives off a slip.
 * The sheaths on the Recti are gradually lost in the perimysium, but they give off important expansions.
 * The expansion from the Rectus superior blends with the tendon of the Levator palpebrae; that of the Rectus inferior is attached to the inferior tarsus.
 * The expansions from the sheaths of the Recti lateralis and medialis are strong.
 * lateral check ligament is the fibrous expansion from the sheath of recti lateralis.
 * medial check ligament is the fibrous expansion from the sheath of recti medialis.
 * the lateral check ligament attached to zygomatic bones
 *  the medial check ligament attached to the lacrimal bone.


 * The Orbital Fascia forms the periosteum of the orbit.
 * The Orbital Fascia is loosely connected to the bones and can be readily separated from them. * Behind, The Orbital Fascia is united with the dura mater and with the sheath of the optic nerve.
 * In front, The Orbital Fascia is connected with the periosteum at the margin of the orbit, and sends off a process which assists in forming the orbital septum.
 * From The Orbital Fascia two processes are given off; one to enclose the lacrimal gland, the other to hold the pulley of the Obliquus superior in position.

The Eyebrows (supercilia)

 * The Eyebrows are two arched eminences of integument, which surmount the upper circumference of the orbits, and support numerous short, thick hairs, directed obliquely on the surface.
 * The eyebrows consist of thickened integument connected with the Orbicularis oculi muscle, Corrugator muscle, and Frontalis muscles.
 * The Eyelids are two thin, movable folds, placed in front of the eye.
 * The upper eyelid is the larger, and the more movable of the two,
 * The upper eyelid is furnished with the Levator palpebræ superioris'.
 * When the eyelids are open,  the palpebral fissure (rima palpebrarum), is left between their margins,
 * the angles of  the palpebral fissure correspond to the junctions of the upper and lower eyelids.
 * the angles of  the palpebral fissureare called the palpebral commissures or
 * the palpebral commissures is AKA canthus.	  14
 * The lateral palpebral commissure is more acute than the medial,
 * AT The lateral palpebral commissure the eyelids lie in close contact with the bulb of the eye:
 * the lacus lacrimalis is a a triangular space eparating two eyelids at the medial palpebral commissure '''
 * At the basal angles of the lacus lacrimalis, is a small conical elevation, the lacrimal papilla,
 * the apex of the lacrimal papilla is pierced by the punctum lacrimale
 * the punctum lacrimale is the commencement of the lacrimal duct.
 * The eyelashes   are AKA cilia'''.
 * The eyelashes  are attached to the free edges of the eyelids;
 * The eyelashes  are short, thick, curved hairs, arranged in a double or triple row:
 * The eyelashes  of the upper eyelid,are more numerous and longer than those of the lower,
 * The eyelashes  of the upper eyelid curve upward;
 * The eyelashes  of the lower eyelid curve downward
 * Near the attachment of the eyelashes are the openings of  the ciliary glands
 * the openings of  the ciliary glands are arranged in several rows close to the free margin of the lid
 *  the ciliary glands are regarded as enlarged and modified sudoriferous glands.	  16

Structure of the Eyelids

 * The eyelids are composed of integument, areolar tissue, fibers of the Orbicularis oculi, tarsus, orbital septum, tarsal glands and conjunctiva.
 * The upper eyelid has the aponeurosis of the Levator palpebræ superioris (Fig. 893).	  17
 * The integument of the eyelid is extremely thin, and continuous at the margins of the eyelids with the conjunctiva.
 * The subcutaneous areolar tissue of the eyelids is very lax and delicate, and seldom contains any fat.
 * The palpebral fibers of the Orbicularis oculi are thin, pale in color, and possess an involuntary action.
 * The tarsi is AKA tarsal plates(Fig. 894)
 * tarsal plates are two thin, elongated plates of dense connective tissue, about 2.5 cm. in length;
 * A tarsal plate is placed in each eyelid, and contributes to its form and support.
 * The superior tarsus is the larger than the inferior tarsus.
 * The superior tarsus is of a semilunar form, about 10 mm. in breadth at the center, and gradually narrowing toward its extremities.
 * The superior tarsus to the anterior surface of The superior tarsus plate.
 * The inferior tarsus is thin, elliptical in form
 * The inferior tarsus has a vertical diameter of about 5 mm.
 * The ciliary margins of The tarsus are thick and straight.
 * The orbital margins The tarsiare connected to the circumference of the orbit by the orbital septum.
 * The lateral angles of the tarsal plates are attached to the zygomatic bone by the lateral palpebral raphé.
 * The medial angles of the tarsal plates end at the lacus lacrimalis
 * The medial angles of the tarsal plates are attached to the frontal process of the maxilla by the medial palpebral ligament (page 381).
 * The orbital septum is AKA septum orbitale
 * The orbital septum is AKA  palpebral ligament
 * The orbital septum is a membranous sheet, attached to the edge of the orbit,
 * The orbital septum is continuous with the periosteum at the edge of the orbit.
 * In the upper eyelid it blends by its peripheral circumference with the tendon of the Levator palpebræ superioris and the superior tarsus, in the lower eyelid with the inferior tarsus. Medially it is thin, and, becoming separated from the medial palpebral ligament, is fixed to the lacrimal bone immediately behind the lacrimal sac. The septum is perforated by the vessels and nerves which pass from the orbital cavity to the face and scalp. The eyelids are richly supplied with blood.	  22

http://www.bartleby.com/107/Images/large/image892.gif http://www.bartleby.com/107/Images/large/image893.gif
 * FIG. 892– Front of left eye with eyelids separated to show medial canthus. (See enlarged image)
 * FIG. 893– Sagittal section through the upper eyelid. (After Waldeyer.) a. Skin. b. Orbicularis oculi. b’. Marginal fasciculus of Orbicularis (ciliary bundle). c. Levator palpebræ. d. Conjunctiva. e. Tarsus. f. Tarsal gland. g. Sebaceous gland. h. Eyelashes. i. Small hairs of skin. Sweat glands. k. Posterior tarsal glands. (See enlarged image)

The Tarsal Glands (glandulæ tarsales [Meibomi]; Meibomian glands) (Fig. 895)

 * The tarsal glands are situated upon the inner surfaces of the eyelids,
 * The tarsal glands are situated between the tarsi and conjunctiva,
 * The tarsal glands are seen through the conjunctiva on everting the eyelids
 * The tarsal glands present an appearance like parallel strings of pearls.
 * There are about thirty  tarsal glandsin the upper eyelid,
 * The tarsal glands are somewhat fewer in the lower eyelid than upper eyelid.
 * The tarsal glands are imbedded in grooves in the inner surfaces of the tarsi,
 * The tarsal glands 's ducts open on the free magins of the lids by minute foramina.	  23

Structure



 * The tarsal glands are modified sebaceous glands, each consisting of a single straight tube or follicle, with numerous small lateral diverticula.
 * The tubes are supported by a basement membrane, and are lined at their mouths by stratified epithelium; the deeper parts of the tubes and the lateral offshoots are lined by a layer of polyhedral cells.
 * The conjunctiva is the mucous membrane of the eye.
 * The conjunctiva lines the inner surfaces of the eyelids
 * The conjunctiva is reflected over the forepart of the sclera and cornea.
 * The Palpebral Portion of The conjunctiva is AKA tunica conjunctiva palpebrarum
 * tunica conjunctiva palpebrarum is thick, opaque, highly vascular,
 * tunica conjunctiva palpebrarum covered with numerous papillæ, its deeper part presenting a considerable amount of lymphoid tissue.
 * At the margins of the lids tunica conjunctiva palpebrarum becomes continuous with the lining membrane of the ducts of the tarsal glands, the lacrimal ducts, with the lining membrane of the lacrimal sac and nasolacrimal duct.
 * At the lateral angle of the upper eyelid the ducts of the lacrimal gland open on its free surface; * the plica semilunaris is a semilunar fold at the medial angle of the eyelid made by conjunctiva,
 * the superior fornix is The line of reflection of the conjunctiva from the upper eyelid on to the bulb of the eye
 * the inferior fornix is The line of reflection of the conjunctiva from the lower eyelid on to the bulb of the eye

http://www.bartleby.com/107/Images/large/image894.gif http://www.bartleby.com/107/Images/large/image895.gif
 * FIG. 894– The tarsi and their ligaments. Right eye; front view.
 * FIG. 895– The tarsal glands, etc., seen from the inner surface of the eyelids. (See enlarged image)

The Bulbar Portion (tunica conjunctiva bulbi)
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 * the conjunctiva is loosely connected to the bulb of the eye, upon the sclera.
 * tunica conjunctiva bulbi is thin, transparent.
 * tunica conjunctiva bulbi lacks papillae.
 * tunica conjunctiva bulbi is slightly vascular.
 * tunica conjunctiva bulbi consists only of epithelium on the cornea, constituting the epithelium of the cornea.
 * the epithelium of the corneais a transition of epithelium of tunica conjunctiva bulbi.
 * Lymphatics arise in the conjunctiva in a delicate zone around the cornea, and run to the ocular conjunctiva.	  27
 * In and near the fornices of conjunctiva,a number of convoluted tubular glands open on the surface of the conjunctiva.
 * convoluted glands of conjunctiva is more plentiful in the upper than in the lower eyelid,
 * Henle trachoma glands are found in the conjunctiva
 * Henle trachoma glands are chiefly situated near the medial palpebral commissure.
 * Henle trachoma glands are analogous to Peyer’s patches of small intestine.
 * The caruncula lacrimalis is a small, reddish, conical-shaped body
 * The caruncula lacrimalis is situated at the medial palpebral commissure
 * The caruncula lacrimalis is filling up the lacus lacrimalis.
 * The caruncula lacrimalis is consists of a small island of skin containing sebaceous and sudoriferous glands
 * The caruncula lacrimalis is the source of the whitish secretion which constantly collects in this region.
 * A few slender hairs are attached to The caruncula lacrimalis 's surface.
 * the plica semilunaris is a slight semilunar fold of conjunctiva
 * the plica semilunaris locates Lateral to The caruncula lacrimalis
 * the concavity of the semilunar shape ofthe plica semilunaris is directed toward the cornea
 * The nerves in the conjunctiva are numerous and form rich plexuses.
 * According to Krause they terminate in a peculiar form of tactile corpuscle, which he terms “terminal bulb.”

The Lacrimal Apparatus (apparatus lacrimalis) (Fig. 896)

 * The Lacrimal Apparatus consists of (a) the lacrimal glandand its excretory ducts, (b) the lacrimal ducts, the lacrimal sac, and the nasolacrimal duct.

The Lacrimal Gland (glandula lacrimalis)
http://www.bartleby.com/107/Images/large/image896.gif http://www.iovs.org/content/43/9/2923/F10.medium.gif -
 * The lacrimal gland is lodged in the lacrimal fossa on the medial side of the zygomatic process of the frontal bone.
 * The lacrimal gland is of an oval form
 * The lacrimal gland is about the size and shape of an almond,
 * The lacrimal gland consists of the superior lacrimal glands and inferior lacrimal glands.
 * The superior lacrimal gland is connected to the periosteum of the orbit by a few fibrous bands
 * The superior lacrimal gland rests upon the tendons of the Recti superioris and recti lateralis, which separate it from the bulb of the eye.
 * The inferior lacrimal gland is separated from the superior by a tendon of the levator palpebrae ,
 * The inferior lacrimal gland projects into the back part of the upper eyelid,
 * The inferior lacrimal gland 's deep surface is related to the conjunctiva.
 * The ducts of the lacrimal glands are from six to twelve in number
 * The ducts of the lacrimal glands run obliquely beneath the conjunctiva for a short distance,
 * The ducts of the lacrimal glands open along the upper and lateral half of the superior conjunctival fornix.	  32

Structures of the Lacrimal Gland (Fig. 897)
.—In structure and general appearance the lacrimal resembles the serous salivary glands (p. 1136). In the recent state the cells are so crowded with granules that their limits can hardly be defined. They contain oval nuclei, and the cell protoplasm is finely fibrillated. 33



The Lacrimal Ducts (ductus lacrimalis; lacrimal canals)
- -
 * The lacrimal ducts locates one in each eyelid.
 * The lacrimal duct 's oriface is termed  punctum lacrimale.
 *  punctum lacrimale locates on the summit of the papilla lacrimalis.
 * the papilla lacrimalis is seen on the margin of each eye lid, at the lateral the extremity of the lacus lacrimalis.
 * Lacus lacrimalis is a small space at the medial angle of the eye.
 * The superior duct, is the smaller and shorter of the two
 * The superior ductat first ascends, and then bends at an acute angle, and passes medialward and downward to the lacrimal sac.
 * The inferior duct at first descends, and then runs almost horizontally to the lacrimal sac.
 * At the angles they are dilated into ampullae; their walls are dense in structure and their mucous lining is covered by stratified squamous epithelium, placed on a basement membrane.
 * Outside the latter is a layer of striped muscle, continuous with the lacrimal part of the Orbicularis oculi;
 * at the base of each lacrimal papilla the muscular fibers are circularly arranged and form a kind of sphincter.

The Lacrimal Sac (saccus lacrimalis)

 * The lacrimal sac is the upper dilated end of the nasolacrimal duct,
 * The lacrimal sac is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla.
 * The lacrimal sac is oval in form and measures from 12 to 15 mm. in length;
 * The lacrimal sac 's upper end is closed and rounded;
 * The lacrimal sac 's lower is continued into the nasolacrimal duct.
 * The lacrimal sac 's superficial surface is covered by a fibrous expansion derived from the medial palpebral ligament
 * The lacrimal sac 's deep surface is crossed by the lacrimal part of the Orbicularis oculi, which is attached to the crest on the lacrimal bone.

Structure

 * The lacrimal sac consists of a fibrous elastic coat, lined internally by mucous membrane: the latter is continuous, through the lacrimal ducts, with the conjunctiva, and through the nasolacrimal duct with the mucous membrane of the nasal cavity.

The Nasolacrimal Duct (ductus nasolacrimalis; nasal duct)

 * The nasolacrimal duct is a membranous canal, about 18 mm. in length,
 * The nasolacrimal duct extends from the lower part of the lacrimal sac to the inferior meatus of the nose,
 * The nasolacrimal duct ends by a somewhat expanded orifice, provided with an imperfect valve, the plica lacrimalis (Hasneri),
 * the plica lacrimalis  is formed by a fold of the mucous membrane in meatus of the nose.
 * The nasolacrimal duct is contained in an osseous canal, formed by the maxilla, the lacrimal bone, and the inferior nasal concha
 * The nasolacrimal duct is narrower in the middle than at either end, and is directed downward, backward, and a little lateralward.
 * The mucous lining of the lacrimal sac and  nasolacrimal duct is covered with columnar epithelium, which in places is ciliated.	  37


 * FIG. 896– The lacrimal apparatus. Right side. (See enlarged image)

FIG. 897– Alveoli of lacrimal gland. (See enlarged image) Note 148. C. B. Lockwood, Journal of Anatomy and Physiology, vol. xx. [back] Note 149. Wilson, J. G., American Journal of Anatomy, 1911, xi. [back]