In the anantomy of the organs of the senses will be described the organs of sight, hearing, and smell - the higher organs of special sense. The description of the organ of touch is given with the skin, and that of the organ of taste with the tongue.
The pituitary or Schneiderian membrane, which lines the cavities of the nose, is a highly vascular mucous membrane, inseparably united, like that investing the cavity of the tympanum, with the periosteum and perichondrium, over which it lies. It is continuous with the skin through the nostrils; with the mucous membrane of the pharynx through the posterior apertures of the nasal fossae; with the conjunctiva through the nasal duct and lachrymal canaliculi; and with the lining membrane of the several sinuses which communicate with the nasal fossae.
The nasal fossae, and the various openings into them, with the posterior nares, have been previously described as they exist in the skeleton, and the greater part of that description is also applicable generally to the nose in a recent state; but it is proper to mention certain differences in the form and dimension of parts, which depend on the arrangement of the lining membrane, viz.
These are the chief support of the outer part of the organ. They occupy the triangular opening seen in front of the nasal cavity in the dried skull, and assist in forming the septum between the nasal fossae. There are usually reckoned two large and three small cartilages on each side, and one central piece or cartilage of the septum.
The eyelids (palpebrae) are moveable portions of integument, strengthened toward their margins by a thin lamina of dense fibrous tissue. A mucous membrane lines their inner surface, and is reflected thence in the form of a pellucid covering on the surface of the eyeball. This is named the conjunctival membrane or conjunctiva.
The parts which constitute the lachrymal apparatus are the following, viz.: - The gland by which the tears are secreted, situated at the upper and outer side of the orbit, together with its excretory ducts; the two canals into which the fluid is received near the inner angle: and the sac with the nasal duct continued from it, through which the tears pass into the inferior meatus of the nose.
The globe or ball of the eye is a composite structure of spheroidal form, placed in the fore part of the orbital cavity, and receiving the thick stem of the optic nerve behind. The recti and oblique muscles closely surround the greater part of the eyeball, and are capable of changing its position within certain limits: the lids, with the plica semilunaris and caruncle, are in contact with its covering of conjunctiva in front; and behind it is supported by a quantity of loose fat and connective tissue.
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