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].
The lips [labia oris] form the anterior wall of the mouth cavity. The lower lip [labium inferius] is marked off from the chin by the sulcus mentolabialis. The upper lip [labium superius] extends upward to the nose medially and the sulcus nasolabialis laterally. The philtrum is a median groove on the upper lip extending from the septum of the nose above to the labial tubercle [tuberculum labii superioris] below, at the middle of the rima oris. On each side of the rima oris the upper and the lower lips are continuous at the angle of the mouth [angulus oris], which is usually opposite the first premolar teeth. Laterally, the lips are continuous with the cheeks [buccse], which form the lateral walls of the mouth cavity.
Our knowledge of the lymphatic system has been very greatly increased during the past ten years by studies on its mode of development. Previous to 1902 nothing definite was known about the primary development or the mode of growth of the lymphatic system. It was concluded by some (Budge, Gullard and Saxer) that the lymphatics arise from undifferentiated mesenchyme cells; Ranvier believed that they arise from veins by budding of the endothelium; while Sala described them as arising partly from the mesenchyme and partly from venous endothelium.
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