Duct (anatomy)

“ Hence the canal of Wirsung in the adult is a compound product. It includes the duct system developed, in connection with the bile duct, in the head of the gland, forming the intestinal termination of the main duct. Its distal body portion on the other hand is derived from the duct system of the originally larger proximal outgrowth, including the entire peripheral portion which has become secondarily added to the duct of the ventral outgrowth to form together with it the canal of Wirsung. ”

“ This duct arises, as in Teleostei and Amphibia, by the constriction of a hollow ridge of the somatic mesoblast into a canal, which is placed in contiguity with the epiblast, along the line of junction between the mesoblastic somites and the lateral plates of mesoblast. Anteriorly the duct [Pg 816] does not become shut off from the body-cavity, and also bends inwards towards the middle line. The inflected part of the duct is the first rudiment of the pronephros, and very soon becomes considerably dilated relatively to the posterior part of the duct. ”

“ Branch ducts should never be made to enter a main duct on the outer side of a bend, because at this point the pressure of the current of air inside the duct is increased. They should join up on the inside of a bend, where the pressure is reduced. ”

“ By its very nature a duct is a structure which can hardly arise de novo. We must even suppose that the segmental organs of Annelids were themselves transformations of still simpler structures. On the other hand I would point to the development in this very duct amongst Amphibians and Osseous fishes of a glandular portion similar to that of a segmental tube, as an à posteriori proof of its being a metamorphosed segmental tube. ”

“ The upper ends of these numerous involutions unite together and form a string of cells, at first solid, but very soon acquiring a lumen, and becoming a duct which communicates (as it clearly must from its mode of formation) , at numerous points with the pleuro-peritoneal cavity. It is very probable that there is one involution to each segment of the body between the front and hind ends of the Oviduct. This duct is the Wolffian duct, which thus, together with the Oviduct, is formed before the appearance of the external gills. ”

“ At such times as the pipe became uncoupled inside the duct line, the part remaining inside was recovered by the use of the tool shown at D, Fig. 15, called a “weasel.” In two instances, the mandrel became stuck in such a manner that the duct line had to be cut into in order to take it out.
The best day’s work of the rodding gang (1 foreman and 4 men) was 20,400 duct ft. of the 4-way conduit in the telegraph and telephone line, and 19,200 duct ft. of single conduit on the low-tension line, an average day’s work under ordinary conditions being about 10,000 duct ft. ”

“ That the method which be has invented 'for securing the proper feed under all circumstances' without 'objectionable features is to make the bore of the duct of comparatively large size and then restrict the duct by means of a wire or rod preferably centrally located therein to leave a channel of the proper size.'
'This arrangement is simple; but in a long experience it has been found to be entirely successful. It is possible to secure the correct drop-by-drop feed with a duct of considerable size, since the friction of the water on the large area of the tube-wall and wire reduces its flow. ”

“ As intimated, especially if the cells of the duct are still in situ, it is impossible to follow the fine nerve-fibres any further. By pressing out the cells from the ducts, one can obtain portion of the duct, with the capillaries belonging to them, but they are short pieces, and the nerve fibril is not easily discoverable. ”

“ There; an emergency pressure duct, designed to open automatically in the event of malfunction of the ship's atmospheric regulators. Emergency pressure could be built up through the ducts in the event of any sudden fall of more than eight ounces per square inch; and would be instantly released should it mount more than three pounds above. All he had to do was jam this single duct to the "excess" position and hold his breath.
It was like picking a lock with his bare fingers, and they felt like fat sausages. ”

“ In the 657,000 duct ft. of conduit in the river tunnels only eight serious obstructions were met. That the work was of exceptionally high quality is shown by the fact that a heavy 3-in. lead cable has been passed through from manhole to manhole (450 ft.) in 6 min., and the company, engaged to lay the cables in these ducts, broke all its previous records for laying, not only for tunnel work, but also in the open.
Fig. 1, Plate XXXV, shows a collection of the tools and arrangements used in laying and rodding ducts. ”

“ Small lateral branches proceeded from different parts of the stem, not exceeding two or three inches in length, nor a quarter of an inch in diameter at the points of insertion. They were conical, and ended in points, gradually bending downwards. Internally they were hollow, and opened into the principal duct, which, except in dimensions, they perfectly resembled. ”

“ But if the tube is large, or its sides are thin, and you bend it without proper precautions, the force you employ entirely destroys its cylindrical form, and the bent part exhibits nothing but a double flattening,—a canal, more or less compressed. To avoid this deformity it is necessary, first, to seal the tube at one extremity, and then, while giving it a certain curvature, to blow cautiously by the other extremity, which for convenience sake should previously be drawn out. ”

“ The reader will have been struck with the similarity between this aqueduct and those of ancient Rome; it remains to be shown that there is one other point of resemblance, in the air-shafts that are built at intervals of a mile. They rise 14 feet above the ground, and, like the old Roman ones, are in the form of towers. Every third one is provided with a door and way of access into the conduit. But the conduit is without the filtering-places and the angles. ”

“ The art of making it has been lost. The conduits, always covered, were carried on arcades only where it was necessary to cross a valley or a plain above its level; for the rest of their way they ran in places upon the surface of the ground, but mostly below it. Thus of the 58 miles of the Anio Novus, 49 were underground. No two aqueducts were on the same level, and so, where their courses converged, it was both possible and convenient to carry one conduit upon another, because it was forbidden by law to erect a building within a certain number of feet on either side of an aqueduct ”

“ A tube of rectangular section has the advantage of greater depth than a solid rod of the same weight; and if the bottom of the tube be strong enough to resist the extension, and the top strong enough to resist the compression, the girder will be stiff and strong.
468. In the Menai Tubular Bridge, where a gigantic tube supported at each end bridges over a span of four hundred and sixty feet, special arrangements have been made for strengthening the top. It is formed of cells, as wrought iron disposed in this way is especially adapted for resisting compression. ”

“ That a tube may be regular in the bore, it is not necessary that the bore be cylindrical; it is sufficiently accurate when equal lengths correspond to equal capacities. A tube with a flat canal, for example, can be perfectly accurate without at all approaching the cylindrical form. It is only necessary that a drop of mercury occupy everywhere the same length. We may observe, by,the way, that, in flat canals, the flattening should be always in the same plane. ”

“ The level of the pipes being thus adjusted, they will not be sprung out of place by the force generated at the descent and at the rising. For a strong current of air is generated in an aqueduct which bursts its way even through stones unless the water is let in slowly and sparingly from the source at first, and checked at the elbows or turns by bands, or by the weight of sand ballast. ”

“ This water was very abundant, but it appeared more like the continuous stream of an aqueduct than a natural spring of water; it was at a very low level, quite 30 ft. underground. At a considerably higher level, and near the surface of the ground, was an aperture into the brick specus or conduit of an aqueduct of the third century, in which the water was flowing steadily along from west to east; this continued all the summer of 1874, and the water was always flowing. This aperture was closed in the summer of 1875, and the whole specus buried again ”

“ These canals, reservoirs, or stagna, were brought out more clearly in 1875, and the substructures which supported them were then made visible [73] .
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In the corridors are many remains of the open channels for the water brought from the aqueducts. They are not more than a foot deep, often not so much, being frequently much worn: when perfect they are nearly of that depth, and are lined with the peculiar cement used only for the aqueducts, called Opus signinum, and in Italian, Coccio-pesto. This is an invariable mark of an aqueduct ”

“ This goes on year after year underground, new tubes always travelling outwards till the circle widens and widens like the rings of water on a pond, only that it spreads very slowly, making a new ring each year, which is often composed of a mass of tubes as much as a foot thick in the ground, and the tender tubes in the centre die away as the new ones form a larger hoop outside. ”

“ The level of this branch pipe is about 120 feet below the bottom of the Aqueduct on the north side of the valley; affording an opportunity for a beautiful jet d’eau;—such an one as cannot be obtained at the fountains in the city. From an orifice of seven inches diameter the column of water rises to a height of 115 feet when there is only a depth of 2 feet of water in the Aqueduct. ”

“ A description from such source, accompanied with detailed plans of all the appurtenances of the Aqueduct, with the results of experiments on the flow of water in the Aqueduct, would be a useful contribution to the cause of science, a valuable work to Engineers generally, and particularly so to younger members of the profession. ”

“ The ducts were laid on beds of mortar, and were made to break joints at top and bottom and side to side with the adjacent ducts. They were laid with a wooden mandrel; a square leather washer at the near end acted as a cleanser when the mandrel was pulled through.
The specifications required the ducts to be laid at the same time as the concrete and be carried up with it, but this was found to be a very awkward operation, as the tamping of the concrete and the [Pg 204] walking of men disturbed the ducts, especially as the bonds lay across them. ”

“ But many have not been content to confine themselves to their limits, but have laid hands on the aqueducts themselves by puncturing, here and there, the side walls of the channels, not merely those who have secured a right to draw water, but also those who misuse the occasion of the least favour for attacking the walls of the conduits. ”

“ The central span of the viaduct is an arch of 220 ft. span between abutments, and about 90 ft. height; the remainder of the space on each side is divided into two spans by an iron pier at a distance of 68 ft. from the retaining wall. These piers are 36 ft. 2 in. high, and carry girders 144 ft. long, balanced each on a pivot in the center. One end of these girders is secured to the retaining walls by means of horizontal and vertical anchorages, while the other end rests in a sliding bearing on the top flange of the arch. ”

“ The most important purpose for which aqueducts are constructed is that of conveying pure water, from sources more or less distant, to large masses of population. Aqueducts are either below ground, on the surface, or raised on walls either solid or pierced with arches ”

“ The abutments have a foundation of solid rock which was excavated in proper form to give them firm footing. The whole structure presents a degree of stability which seems to defy the effects of time. The Aqueduct has a cast iron lining over this bridge (as it has over all of this character) : it is formed of plates five eighths of an inch thick, put together with screw-bolts and nuts and the joints closely filled with iron cement. This lining is within the brick work of the bottom and sides of the channel-way, having four inches of brick outside of it and four inside. ”

“ This Aqueduct is formed by two ranges of arches; those in the lower tier are seventy in number, and each 28 feet span; the piers of these arches are each 12 feet thick. The arches of the second or upper tier are much smaller, and are arranged so that three of them come within the space occupied by one of the lower arches. They are 9 feet diameter; their piers are 4 feet and a quarter thick. ”

“ BLOODVESSELS. It was somewhat surprising to me, and not a little interesting, to find that the ducts have a decidedly richer blood supply than the gland substance proper, the meshes of the capillaries covering the ducts very closely indeed.
I will also call attention to the fact that, along the terminal portions of the ducts, no arteries or veins can be seen; and what is still more important, no free nerve-fibres can be discovered. ”

“ Secondly, water from clay pipes is much more wholesome than that which is conducted through lead pipes, because lead is found to be harmful for the reason that white lead is derived from it, and this is said to be hurtful to the human system. ”

“ Apply this spinal branch of phrenology to the Sperm Whale. His cranial cavity is continuous with the first neck-vertebra; and in that vertebra the bottom of the spinal canal will measure ten inches across, being eight in height, and of a triangular figure with the base downwards. As it passes through the remaining vertebrae the canal tapers in size, but for a considerable distance remains of large capacity. Now, of course, this canal is filled with much the same strangely fibrous substance—the spinal cord—as the brain; and directly communicates with the brain. ”