THE KIDNEYS

                     

THE Kidneys, two in number, are situated in the back part of the abdomen, and are for the purpose of separating from the blood certain materials which, when dissolved in a quantity of water, also separated from the blood by the kid- neys, constitute the urine.                                                              _ They are placed in the loins, one on each side of the vertebral column, behind the peritoneum, and surrounded by a mass of fat and loose areolar tissue. Theil' upper extremity is on a level with the upper border of the twelfth dorsal vertebra, their lower extremity on a level with the third lumbar. The right kidney is usually on a slightly lower level than the left, probably on account of the vicinity of the liver. Each kidney is about four inches in length, two to two and a half in breadth, and rather more than one inch in thickness. 'I'he left is somewhat longer, though narrower, than the right. The weight of the kidney in the adult male varies from 4t ounces to 6 ounces; in the adult female, from 4 ounces to 5t ounces. The com­bined weight of the two kidneys in proportion to the body is about 1 in 240. The kidney has a characteristic form. It is flattened on its sides and presents at one part of its circumference a hollow. It is larger at its upper than its lower extremity. It presents for examination two surfaces, two borders, and an upper and lower extremity. Its anterior surface is convex, looks forward and outward. and is partially covered by peritoneum. The right kidney in its upper three-fourths is in con­tact with the posterior part of the under surface of the right lobe of the liver. on which it produces a concave impression, the impreesio renalis (page 918). Toward its inner border it is covered by the second part of the duodenum, while its lower and outer part is in relation with the hepatic flexure of the colon. 'I'he relation of the second part of the duodenum to the front of thc right kidney is a varying one. The left kidney is covered above by the posterior surface of the stomach, below the stomach by the pancreas, behind which are the splenic vessels. Its lower half is in contact with some of the coils of the small intestine and some­times with the third part of the duodenum. Near its outer border the anterior sur­face lies behind the spleen and the splenic flexure of the colon.

THE THYROID GLAND. The thyroid gland is classified with the thymus, suprarenal capsules. and pleen, und" 'h, head of du,t/", g/o"U-i. e., glana, which do not pa",,, an """a,y duct. From its situation in connection with the trachea and larynx, the thyroid body is usually described with those organs, although it takes no part in the func­tion of respiration. It is situated at the front and sides of the neck, and consists of two lateral lobes connected aCl'OSS the middle line by a narrow tran"verse portion, the isthmu8. The weight of the gland is soinewhat variable, but is usually about one ounce. It is somewhat heavier in the female, in whom it becomes enlarged during men­struation and pregnancy. The lobes are conical in shape, the apex of each being directed upward and outward as far as the junction of the middle with the lower third of the thyroid cartilage; the base looks downward, and is on a level with the fifth or sixth tracheal ring. 'I'he external or Superficial 8urface is convex, and covered by the skin, the superficial and deep £'1scia, the Sterno-mastoid, the anterior belly of the Omo­hyoid, the Sterno-hyoid and Sterno-thyroid muscles, and beneath the last muscle by the pre-tracheal layer of the deep fascia, which forms a capsule for the gland. The deep or internal surface is moulded over the underlying structures, viz., the thyroid and cricoid cartilages, the trachea, the inferior constrictor and posterior part of the Crico-thyroid muscles, the reSop}lagus (particularly on the left side of the nook), 'h, '"p";a, and inf,na, ,hy,a;d "''';'', and the "'n''On' laryngoal nerves, Its anterior border is thin, and inclines obliquely from above downward and inward toward the middle line of the neck, while the posterior border is thick and overlaps the common carotid artery. Each lobe is a bout two inches in length, its greatest width is about one inch and a quarter, and its' thickness about' three quarters of all inch.

THE TEETH

The human teeth are arranged in two parabolic arches, the upper arch being larger, its teeth overlapping the lower. The average distance between the centres of the condyles of the inferior maxillary bones is about four inches. which is also the distance from either of these points to the line of junction between the lower incisor teeth

Owing to the smaller sizes of the lower incisors, the teeth of the lower jaw are each one half a tooth in advance of its upper fellow, so that each tooth of the dental series has two antagonists, with the exception of the lower central incisors a.nd upper third molars

The third molars are called the wisdom teeth (dentes sapientia!) from their late eruption: they have threc cusps upon the upper and five upon the lower. The three roots of the upper are frequently fused together, forming a grooved cone, which is usually curved backward. The roots of the lower, two in number, are compressed together and curve backward

The crowns are cuboidal in form, are convex buccally and 1inguall:-; they are flattened mesially and distally. They are formed by the fusion of three primitive cuspids in the upper and four in the lower. '1'0 these are added in the first and . second upper molars a disto-lingual tubercle, and in the first and third molars of the lower jaw a disto-buccal tubercle. The unions of the primiti\'e forms are marked by sulci. The necks of these teeth are large and rhomboidal in form. The roots of the Uppel' molars are three in number-one large lingual and two smaller buccal roots. In the lower, two roots are found, a mesial and a distal, each of which is much flattened from before backward.

THE LUNGS.

The color of the lungs at birth is a pinkish-white; in adult life a dark slate-color, mottled in patches; and as age advances this mottling assumes a black color. The coloring matter consists of granules of a carbonaceous substance deposited in the areolar tissue near the surface of the organ. It increases in quantity as age advances, and is more abundant in males than in females. The posterior border of the lung is usually darker than the anterior. 'I'he surface of the lung is smooth, shining, and marked out into numerous polyhedral spaces, indicating the lobules of the organ; the area of each of these spaces is crossed by numerous lighter lines. The substance of the lung is of a light, porous, spongy texture; it floats in water and crepitates when handled, owing to the presence of air in the tissue; it is also highly elastic; hence the collapsed state of these organs when they are removed from the closed cavity of the thorax. Structure.-The lungs are composed of an external serous coat, a subserous areolar tissue, and the pulmonary substance or parenchyma. The serous coat is derived from the pleura; it is thin, transparent, and invests the entire organ as far as the root. The subserous areolar tissue contains a large proportion of elastic fibres; it invests the entire surfa.ce of the lung, and extends inward between the lobules. 'I'he parenchyma is composed of lobules which, although closely connected together by an interlobular areolar tissue, are quite distinct from one another, and may be teased asunder without much difficulty in the fostus. The lobules vary in size; those on the surface are large, of pyramidal form, the base turned toward the surface; those in the interior, smaller and of various forms. Each lobule is composed of one of the ramifications of a bronchial tube and its terminal air-cells, and of the ramifications of the pulmonary and bronchial vessels, lymphatics, and nerves, all of these structures being connected together by areolar tissue.

The color of the lungs at birth is a pinkish-white; in adult life a dark

slate-color, mottled in patches; and as age advances this mottling assumes a black color. The coloring matter consists of granules of a carbonaceous substance deposited in the areolar tissue near the surface of the organ. It increases in quantity as age advances, and is more abundant in males than in females. The posterior border of the lung is usually darker than the anterior.

'I'he surface of the lung is smooth, shining, and marked out into numerous polyhedral spaces, indicating the lobules of the organ; the area of each of these spaces is crossed by numerous lighter lines.

The substance of the lung is of a light, porous, spongy texture; it floats in

water and crepitates when handled, owing to the presence of air in the tissue; it is also highly elastic; hence the collapsed state of these organs when they are removed from the closed cavity of the thorax.

Structure.-The lungs are composed of an external serous coat, a subserous

areolar tissue, and the pulmonary substance or parenchyma.

The serous coat is derived from the pleura; it is thin, transparent, and invests

the entire organ as far as the root.

The subserous areolar tissue contains a large proportion of elastic fibres; it

invests the entire surfa.ce of the lung, and extends inward between the lobules.

'I'he parenchyma is composed of lobules which, although closely connected together by an interlobular areolar tissue, are quite distinct from one another, and may be teased asunder without much difficulty in the fostus. The lobules vary in size; those on the surface are large, of pyramidal form, the base turned toward the surface; those in the interior, smaller and of various forms. Each lobule is composed of one of the ramifications of a bronchial tube and its terminal air-cells, and of the ramifications of the pulmonary and bronchial vessels, lymphatics, and nerves, all of these structures being connected together by areolar tissue.

THE SPLEEN

               
     

The Spleen belongs to that class of bodies which are known as ductless [llands. It is probably related to the blood-vascular system, but in consequence of its anatomical relationship to the stomach and its physiological relationship to the liver it is convenient to describe it in this place. It is situated principally in the left hypochondriac region, its Upper and inner extremity extending into the epigas­tric region; lying between the fundus of the stomach and the Diaphragm. It is the largest of the ductless glands, and measures some five or six inches in length. It is of an oblong, flattened form, soft, of very brittle consistence, highly vascular, and of a dark purplish color. The upper end is directed inward, toward the vertebral column, where it lies on a level with the eleventh dorsal vertebra. The lower end, sometimes termed the basal surface, is flat, triangular in shape, and rests Upon the splenic flexure of the colon and the phreno-colic ligament, and is genernlly in contact with the tail of the pancreas. The anterior border is free, sharp, and thin, and is often notched, especially below. It separates the phrenic from the gastric surface. The posterior border is more rounded and blunter than the anterior. It separates the renal por­tion of the internal surface from the phrenic surface. It corresponds. to the lower border of the eleventh rib and lies between the Diaphragm and left k1dney. The internal border is the name sometimes given to the ridge which separates the renal and gastric portions of the internal surface.

THE CONNECTIVE TISSUES

have developed to the practical exclusion of the other elements. It is found in the ligamenta subflava, in the vocal cords, in the longitudinal coat of the trachea and bronchi, in the inner coats of-the blood-vessels, especially the larger arteries, a.nd to a very co.nsiderable ex~ent in t~e thyro-hyoid, crico-thyroid, and ~tylo-hy~id ligaments. It IS also found In the ligamentum nuchre of the lower animals (FIg. 614). In some parts, where the fibres are broad and .Iarge and the netwo.rk close, the tissue presents the appearance of a membrane, with gaps or perforatIOns cor­responding to the intervening space. This is to be found in the i~ner coat of the arteries, and to it the name of fenestrated membrane has been given by Henle. The yellow elastic fibres remain unaltered by acetic acid.

THE LIVER

            

The hepatic cells are of more or less spheroidal form, but may be rounded, flattened, or many-sided from mutual compression. They vary in size from the n\o to the ~ of an inch in diameter. They consist of a honeycomb net­work (Klein) without any cell-wall, and contain one or sometimes two distinct nuclei. In the nucleus is a highly refracting nucleolus with granules. Embedded in the honeycomb network are numerous yellow particles, the coloring matter of the bile, and oil-globules. The cells adhere together by their surfaces so as to form rows, which radiate from the centre to the circumference of the lobules.' As stated above, they are the chief agents in the secretion of the bile.  The Blood-vessels.-The blood in the capillary plexus around the liver­cells is brought to the liver principally by the portal vein, but also to a certain extent by the hepatic artery. For the sake of clearness the distribution of the blood derived from the hepatic artery may be considered first.