monary artery, and is formed by left superior cardiac, left inferior cardiac of pneumogastric, and branches from deep cardiac plexus. Coronary, the posterior, chiefly from deep, the anterior from superficial cardiac plexus. Accuking R. 2. Chern.az Aortic, on sides and front of vessel between roots of superior and inferior mesenteric arteries. Hypogastric, lying in front of sacrum, between common iliac arteries, it supplies the pelvic viscera, and is formed by filaments from aortic plexus, and from lumbar and first two sacral ganglia, contains no ganglia, and divides into two lateral portions, forming the inferior hypogastric or pelvic plexuses. Inferior hypogastric plexuses. These lie upon each side of rectum and bladder (rectum, vagina, and bladder, in females), and each is formed by a continuation of the hypogastric plexus and branches from second, third, and fourth sacral nerves, and a few filaments from sacral ganglia; the branches accompany those of internal iliac artery, and are distributed to all the pelvic viscera; their branches are Any of the internal organs with their appendages, contained within the cranial, thoracic, or abdominal cavities. Of what does the digestive apparatus consist? Of the alimentary canal, a musculo-membranous tube, lined with mucous membrane, about thirty feet long, and extending from the mouth to the anus, and certain accessory organs. Name the subdivisions of the alimentary canal. Mouth, pharynx, oesophagus, stomach, small intestine (duodenum, jejunum, ilium), large intestine (cæcum, colon, rectum). What are the accessory organs? The teeth, salivary glands (parotid, submaxillary, sublingual), liver, pancreas, and spleen. What is their function? The Teeth. To reduce the food to fragments, thus enabling the digestive fluids to act to best advantage. Into what classes are they divided? Into Temporary, or milk teeth, ten in each jaw, viz., four incisors, two canines, and four molars; Permanent teeth, sixteen in each jaw, viz., four incisors, two canines, four bicuspids or premolars, six molars. Of what parts does every tooth consist? Of a Crown or body (Fig. 82), that part projecting above the gum. *Fang, or root, that part occupying the alveolus, held there by the periodontium (periosteum), lining the socket; in addition, the teeth are steadied by the gums, composed of dense fibrous tissue covered with mucous membrane. Pulp-cavity, an interior cavity filled with the tooth-pulp, a vascular connective tissue with numerous nerves, both arteries and nerves reaching the pulp by a canal opening at apex of fang. Describe the characteristics of each of the four varieties of teeth. Incisor or cutting teeth. The crown is wedge-shaped, convex in front, bevelled and slightly concave behind; the fang is single, long, conical, and transversely flattened. Canines. Crown is large, conical, convex in front, rises above level of other teeth; fang long, conical, compressed laterally; upper pair are called in common parlance "eye teeth," the lower 'stomach-teeth." Bicuspids. Crown has two-projecting cusps, fang generally is single, laterally grooved with bifid apex; they are also called premolars. Molar (grinders). Crown nearly cubical, with four cusps in upper, and five in lower molars; fangs, usually three for first two upper, and two for first two lower molars; the third molar is called the "wisdom tooth" (dens sapientia), from its late appearance, and usually has but one fang with grooves indicating a tendency to formation of three fangs in upper, two in lower jaw. FIG. 82. The second temporary molar is the largest milk tooth, and is succeeded by the second permanent bicuspid. Describe the structure of a tooth. Each is formed chiefly of Dentine, or ivory', composed of minute, wavy, branching tubes, called dental tubuli, embedded in a hard, homogeneous substance, the intertubular tissue. The tubules are about 5th of an inch in diameter, dividing dichotomously, giving the wavy appear ance of the cut surface, and open into the pulp cavity. Chemically dentine consists of twenty-eight parts of animal, and seventy-two of earthy matter. Enamel1 forms a thin crust over crown, is the densest of all animal tissues, containing only 3.5 per cent. of animal matter, and is composed of minute parallel hexagonal rods, about 50th of an inch in diameter, pursuing a wavy course. Cement, or crusta petrosa, is a layer of true bone commencing at the neck and becoming thicker toward apex of fang. Pulp, filling the pulp-cavity, consisting of soft, very vascular connective tissue, with numerous nerves and cells, the latter being 12 Wisdom. of two kinds, columnar, called odontoblasts—arranged in a layer lining pulp-cavity-and fusiform cells wedged in between these or permeating the pulp, both having fine processes, said to be prolonged into the dentinal tubules. Whence do the teeth obtain their blood and nerve supply? From the alveolar and infraorbital branches of internal maxillary, and from inferior dental artery; the nerves come from the anterior and posterior dental branches of the superior maxillary, and from the inferior maxillary division of the fifth nerve When do the temporary teeth appear? The time is variable, but, according to the latest authority, they crupt as follows, expressed in months: 7 3 The order of their appearance is first, lower central incisors; then upper central incisors, closely followed by laterals; then lower laterals; next upper anterior molars followed by lower; then upper canines followed by lower; finally, lower back molars, followed by upper. Describe the order of appearance of the permanent teeth. The first to appear are first molars at end of sixth year, the lower teeth usually preceding the upper; thus, expressed in years, these teeth erupt as follows: 6 3 2 2 3 Upper 17-21 12-13 62 10 9 11-12 8 7 7 8 11-12 9 Lower 17-21 12-13 62 10 9 11-12 8 7 7 8 11-12 9 10 62 12-13 17-21 10 62 12-13 17-21 Wisdom Describe the development of the teeth. About the seventh foetal week appears a depression in each jaw, the primitive dental groove, from the bottom of which is developed a ridge which, atrophying at intervals, leaves a row of projecting papillæ, containing odontoblasts, which become capped with epithelial masses developed from the margins and sides of the groove, the enamel organ. Now the groove becomes converted into follicles, each containing a papilla, by contraction and projection of its margins and the ingrowth of membranous septæ. About the thirteenth week the papillæ grow rapidly, the follicles deepen and become closed in by the coalescence of from two to five small membranous outgrowths springing from their margins, called opercula. The lips of the dental groove advance and fuse, completing the saccular stage about the end of the fifteenth week. The more superficial portion of the groove remains open, leaving the secondary dental groove, in which ten lunated depressions appear behind each of the sacs of the milk teeth, for the ten anterior permanent teeth; the secondary groove closes in like the primary one, the follicles becoming cavities of reserve, into which papillæ grow to be closed in as for the temporary teeth; the remaining teeth arise from successive expansions backward of the primitive dental groove. The dentine forms from without inward capped with enamel, and by the gradual growth of the fang the crown produces absorption by pressure upon the overlying bone and mucous membrane, when eruption occurs; the cementum is formed by the periodontal membrane last of all, increasing up to old age. What is the mouth? The Mouth. It is an ovoid cavity in which food is masticated, bounded by lips in front, by cheeks and alveolar processes of both jaws with their contained teeth at sides, by hard and soft palate above, by tongue and floor of mouth below, and terminates at the anterior pillars of the fauces where it opens into pharynx by fauces, and is lined by mucous membrane covered by scaly stratified epithelium containing numerous racemose glands, continuous with external skin; it presents for examination |