Muscles.. D, biceps cruris ; E, gendui or coleus mus cles ; G, tibia/is anticus ; extensor pollicis pedis proprius ; 1, 1, the interosseus ligament ; K, L, 11711I, extensor digitorum lon.c118, with its tendons ; I', pero yens brevis ; Q, peroneus longus ; I?, T, X, exten sor brevis digitorum pedis ; Y, Z, infe•os.sei.
b, superior external articular artery ; c, inferior external articular artery ; d d, superior inter nal articular ; e, inferior internal articular ; i i, anterior tibial artery ; / I, its anastomosis, with branches of the posterior tibial ; p, a branch of the peroneal artery, in osculating with a branch of the anterior tibial ; a branch of the anterior tibial going to the tarsus ; H, an other going to the metatarsus ; the dorsal artery of the great toe ; the plantar artery.
Of the ORGANS of ABSORPTION.
To convey the nutritious particles of the food sepa rated in the stomach and alimentary canal, to the gene ral mass of circulating fluids, the body is provided with numerous small vessels that open into the cavity of the intestines, traverse the mesentery, where they pass through what are called the mesenteric glands, from which they again emerge, and gradually unite in larger tubes, till they all centre in one vessel that lies beside the ascending versa cava, and carries its contents into the left subclavian vein. These vessels have been called lacteals, from the fluid they contain being of a milky colour. Numerous vessels of a similar structure take their origin from all the principal cavities of the body, and probably from every part of its surface. These take up the fluids that have been separated from the general mass of blood, and which are no longer adapted to the purposes for which they were separated, or are excre mentitious, and would prove injurious to the system, if retained. These vessels carry the matters they receive to the same general trunk with the lacteals, and most of them pass into bodies, of a roundish form and glan dular appearance. These vessels are called lymphatics, and the bodies through which they pass lymphatic glands. The general trunk in which the lacteals and lymMatics ultimately meet, is called the thoracic duct, as its course is chiefly confined to the thorax or chest. The lacteals,
mesenteric glands, lymphatic glands, and thoracic duct, constitute the organs of absorption, or the absorbent sys tem.
The lacteals and lymphatics (see Plate XX.) are so nearly alike in structure, disposition, and uses, that we shall consider them together under the general head of absorbent vessels. These are extremely minute, and so transparent, that in their natural state they are scarce ly discernible Ly the naked eye ; though, while the lacteals are filled with chyle, or when any of the absor bents are injected with an opaque fluid, such as mercu ry, they are very perceptible. \Ve then find that they am cylindrical tubes, resembling the small branches of veins in the thinness and flaccidity of their sides ; but having more ofa jointed appearance, owing to the greater number of valves, which are thickly set within their cavities. Their sides, though extremely thin, appear to be of considerable strength, and so lar as can be ascer tained, from an examination of the thoracic duct, they are composed of two coats ; an inner membrane, that is extremely fine and delicate, resembling the internal membrane of the veins, and an outer coat, giving them their strength and elasticity. Sonic anatomists have supposed that this outer coat contains muscular fibres, but the presence of these has not been proved. As there is no doubt, however, that the absorbents possess a power of contracting when irritated, it is probable that their external coat is of a muscular texture. See Cruikshank on the 4bsorbents, 2d ed. p. 62.
The valves of the absorbents, like those of the veins, are arranged in pairs, at very short and generally regu lar intervals. Bichat supposes them to be formed by dou blings of the proper or external coat of the absorbents.
The absorbent vessels run from the points where they originate, in a serpentine direction, and as they pass, they frequently unite with each other, sometimes form ing an intricate net-work, Like the veins, they are most numerous at their origin, and after passing through glands, they become less numerous. The ramifications almost always unite at very acute angles, in this respect resembling those of the nerves.