pages 1021

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 (Fig. 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.

1c. 3. The Accessory Organs of the Eye

(Organa Oculi Accessoria)

The accessory organs of the eye include the ocular muscles, the fasciæ, the eyebrows, the eyelids, the conjunctiva, and the lacrimal apparatus.

The Ocular Muscles (musculi oculi).—The ocular muscles are the:

Levator palpebræ superioris		Rectus medialis.
Rectus superior.		Rectus lateralis.
Rectus inferior.		Obliquus superior.
Obliquus inferior.

FIG. 888– Sagittal section of right orbital cavity. (See enlarged image)

The Levator palpebræ superioris (Fig. 888) is thin, flat, and triangular in shape. It arises from the under surface of the small wing of the sphenoid, above and in front of the optic foramen, from which it is separated by the origin of the Rectus superior. At its origin, it is narrow and tendinous, but soon becomes broad and fleshy, and ends anteriorly in a wide aponeurosis which splits into three lamellæ. The superficial lamella blends with the upper part of the orbital septum, and 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, largely made up of non-striped muscular fibers, is inserted into the upper margin of the superior tarsus, while the deepest lamella blends with an expansion from the sheath of the Rectus superior and with it is attached to the superior fornix of the conjunctiva.

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