The crystalline lens, hardened and divided

In the fetus, the lens is nearly spherical, and has a slightly reddish tint; it is soft and breaks down readily on the slightest pressure. A small branch from the arteria centralis retinæ runs forward, as already mentioned, through the vitreous body to the posterior part of the capsule of the lens, where its branches radiate and form a plexiform network, which covers the posterior surface of the capsule, and they are continuous around the margin of the capsule with the vessels of the pupillary membrane, and with those of the iris. In the adult, the lens is colorless, transparent, firm in texture, and devoid of vessels. In old age it becomes flattened on both surfaces, slightly opaque, of an amber tint, and increased in density (886).

 

Vessels and Nerves.—The arteries of the bulb of the eye are the long, short, and anterior ciliary arteries, and the arteria centralis retinæ. They have already been described (see p. 571).

The ciliary veins are seen on the outer surface of the choroid, and are named, from their arrangement, the venæ vorticosæ; they converge to four or five equidistant trunks which pierce the sclera midway between the sclero-corneal junction and the porus opticus. Another set of veins accompanies the anterior ciliary arteries. All of these veins open into the ophthalmic veins.

The ciliary nerves are derived from the nasociliary nerve and from the ciliary ganglion.

 

Additional eye structures include: extrinsic muscles of eyeball, eyebrows, eyelids, conjuctiva, lacrimal apparatus.

Extraocular Musculature

Levator palpebrae superioris

  • Origin: inferior aspect of the lesser wing of sphenoid (adjacent to the common annular tendon) •Insertion:

1.medial and lateral walls of the orbit 2.superior tarsus

  • Action: elevates the eyelid •Blood: branches of ophthalmic artery •Nerve: oculomotornerve (III cranial)

 

Lateral rectus

  • Origin:

1.common annular tendon (which comes off the body and lesser wing of sphenoid) 2.margins of the optic canal

  • Insert: posterior to the sclerocornealjunction (each muscle inserting along its own directional axis) •Action: abducts eye •Blood: branches of ophthalmic artery •Nerve: abducensnerve (VI cranial)

 

Medial rectus

  • Origin:

1.common annular tendon (which comes off the body and lesser wing of sphenoid) 2.margins of the optic canal

  • Insert: posterior to the sclerocornealjunction (each muscle inserting along its own directional axis) •Action: adducts eye •Blood: branches of ophthalmic artery •Nerve: oculomotornerve (III cranial)

 

Superior rectus

  • Origin:

1.common annular tendon (which comes off the body and lesser wing of sphenoid) 2.margins of the optic canal

  • Insert: posterior to the sclerocornealjunction (each muscle inserting along its own directional axis) •Action:

1.elevates 2.medially rotates 3.adducts the eye

  • Blood: branches of ophthalmic artery •Nerve: oculomotornerve (III cranial)

 

Superior rectus

  • Origin:

1.common annular tendon (which comes off the body and lesser wing of sphenoid) 2.margins of the optic canal

  • Insert: posterior to the sclerocornealjunction (each muscle inserting along its own directional axis) •Action:

1.elevates 2.medially rotates 3.adducts the eye

  • Blood: branches of ophthalmic artery •Nerve: oculomotornerve (III cranial)

 

Inferior rectus

  • Origin:

1.common annular tendon (which comes off the body and lesser wing of sphenoid) 2.margins of the optic canal

  • Insert: posterior to the sclerocornealjunction (each muscle inserting along its own directional axis) •Action:

1.depress 2.laterally rotates 3.adducts the eye

•Blood: branches of ophthalmic artery •Nerve: oculomotor nerve (III cranial)Поділитися цим:

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AnnaR

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Коментарі: 0Публікації: 9Реєстрація: 09-02-2021

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