Buckmaster's Elements of animal physiology / by John Angell.

  • Angell, John
Date:
1866
Catalogue details

Licence: Public Domain Mark

Credit: Buckmaster's Elements of animal physiology / by John Angell. Source: Wellcome Collection.

    340/384 (page 328)
    The Appendages of the Eye comprise the eye- brows, eyelids, conjunctiva, and the lachrymal apparatus, including the lachrymal gland and sac, and the nasal duct. The Eyebrows consist of musculo-cutaneous arches or ridges over the eyes, which are more or less studded with hairs. They shade and protect the eye. The hairs arrest the perspiration which sometimes streams down the forehead, and would otherwise flow into the eyes. They contain fibres from the occipito frontalis, the orbicularis palpebrarum, and the cornigator supercilii muscles. The Palpebr^, or Eyelids, are two thin, flexible, moveable covers or lids for the protection of the front of the eyeball. Each eyelid contains a framework of fibro-cartilage, termed the tarsal cartilage, and consists (passing from without inwards) of very loose skin, areolar tissue, fibres of the orbicularis muscle, tarsal cartilage, fibrous membrane, and of an inner layer (next to the eyeball) of mucous membrane, the conjunctiva. The tarsal car- tilages contain a number of sacculated tubular glands, termed the Meibofnian glands. The edges of the eyelids are also fringed with a row of hairs (the eyelashes), which help to shade and pro- tect the eye. Lachrymal Apparatus.—The lachrymal fluid, or the tears, are secreted by small glands, lodged in depressions at the upper and outer angles of the orbits. After washing the surface of the eye they escape at the opposite angle through the puncta lachry- malia into the lachrymal canals; thence into the lachrymal sacs; and thence into the nasal ducts, which discharge them into the nose. The minute structure of the lachrymal glands resembles that of the salivaiy glands. Muscles of the Eyebrows and Eyelids.—The principal muscles of the eyebrows and eyelids are the orbicularis palpe- braitim, a circular or sphincter muscle, which surrounds the eye and closes the eyelids ; the levatorpalpebra, which raises the eye- lid, and is the direct antagonist to the latter ; the corrugator supercilii, which draws the eyebrow downwards and inwards, and produces the vertical wrinkles in the forehead (it also pro- duces the expression of grief) ; and the tensor tarsi, which draws the eyelid down into the globe of the eye. The Muscles which move the Eyeball (see Fig. 83) are the four recti (straight) muscles, and the superior oblique muscle, which spring from the back oi