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 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 ribs extend from the dorsal portion of the vertebral column to the sternum, forming arches, which enclose the lateral parts of the thorax. They are usually twelve in number at each side, but cases occasionally occur in which the number is augmented by the addition of a cervical or a lumbar rib, to which reference has already been made in describing the vertebras of those regions. The number may also be diminished to eleven. I have lately seen an instance in which this diminution was accompanied with the absence of a dorsal vertebra. The seven superior pairs, which are united by means of cartilaginous prolongations to the sternum, are called sternal or true ribs; the remaining five, which are not prolonged to the sternum, being denominated asternal or false ribs.
The sternum, (os pectoris: xiphoides ; French : le sternum) is situated in the median line, at the fore part of the thorax: it is flat and narrow, but not of equal width in its entire extent, being broad at its upper part, then narrowed somewhat, after which it widens a little; finally it becomes compressed and narrow where it joins the ensiform cartilage. Its direction is oblique from above downwards and forwards; and the inclination forwards, together with the curve backward in the dorsal part of the vertebral column, causes a considerable increase in the anteroposterior diameter of the thorax. We have to consider successively its surfaces, extremities, and borders.
The maxillary bone, (maxilla superior,) is very irregular. It presents an external convex surface, corresponding with the anterior and lateral parts of the face; another, internal, of considerable extent, corresponding with the nasal cavity ; one, superior, smooth, and inclined inwards, forming the floor of the orbit, and surmounted internally by a triangular process, forming the side of the nose ; lastly, a surface which projects horizontally inwards, to form the arch of the palate. The external surface is bounded inferiorly by a thick, dependent border (alveolar), for the lodgment of the teeth; to this as to a common point of union, all the other parts of the bone may be referred.
The oral cavity [cavum oris] represents the first segment of the alimentary canal. Its walls are exceedingly specialized in structure, corresponding to its manifold functions (mastication, insalivation, taste, speech, etc.).
Numerous glands - labial, buccal, palatine and lingual - have already been mentioned, which pour their secretions into the mouth cavity. In addition to these, there are three larger pairs, the salivary glands proper. They include the parotid, the submaxillary, and the sublingual (the latter really a group of glands).
The tongue [latin: lingua; French: La langue] is a muscular organ covered with mucous membrane and located in the floor of the mouth. It is an important organ of mastication, deglutition, taste and speech. Upon its upper surface is a V-shaped groove (sulcus terminalis) indicating the division of the tongue into two parts. The larger anterior part, or body [corpus linguae] belongs to the floor of the mouth, while the smaller posterior part, or root [radix linguae], forms the anterior wall of the oral pharynx. The inferior surface (facies inferior) of the tongue is chiefly attached to the muscles of the floor of the mouth, from the hyoid bone to the mandible. Anteriorly and laterally, however, the inferior surface of the body is free and covered with mucosa. The superior surface of the body is called the dorsum. It is separated from the inferior surface by the lateral margins, which meet anteriorly at the tip [apex linguae].
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