branch, its size is sensibly diminished; and when a vein receives a branch, it is enlarged; but when a lymphatic ramifies, there is generally little change of size, whether the branch given off be large or small.

The lymphatics consist of two planes,-the one superficial, the other deep-seated. The former creep under the outer covering of the organ, or of the skin, and accompany the subcutaneous veins. The latter are seated more deeply in the interstices of the muscles, or even in the tissue of parts; and accompany the nerves and great vessels. These planes anastomose with each other.

This arrangement occurs not only in the limbs, but the trunk, and in every viscus. In the trunk, the superficial plane is seated beneath the skin; and the deep-seated between the muscles and the serous membrane that lines the splanchnic cavities. In the viscera, one plane occupies the surface; the other appears to arise from the parenchyma.

The two great trunks of the lymphatic system, in which the lymphatic vessels of the various parts of the body terminate, are the thoracic duct, and the great lymphatic trunk of the right side. The course of the thoracic duct has been described already. It is formed of three great vessels;-one, in which all the lymphatics and lacteals of the intestines terminate; and the other two, formed by the union of the lymphatics of the lower half of the body. Occasionally, the duct consists of several trunks, which unite into one before reaching the sub

Fig. 257.

clavian vein; but more frequently it is double. In addition to the lymphatics of the lower half of the body, the thoracic duct receives a great part of those of the thorax, and all those from the left half of the upper part of the body. At its termination in the subclavian, there is a valve so disposed as to allow the lymph to pass into the blood; and to prevent the reflux of the blood into the duct. We shall see, however, that its mode of termination in the venous system possesses other advantages. The great lymphatic trunk of the right side is formed by the

Lymphatic Vessels and Glands of the Groin of the absorbents from that side of

Right Side.

abdomen. 3. External pudic vein. 4. Lymphatic ves

vein on its inner side. 5. External trunks of the same

the head and neck, and from the right arm. It is very short, being little more than an inch, and sometimes not a quarter of an inch, in length, but of

1. Saphena magna vein. 2. Veins on the surface of sels collected in fasciculi and accompanying the saphena set of vessels. 6. Lymphatic gland which receives all these vessels. It is placed on the termination of the sabecome deep-seated and accompany the femoral artery. a diameter nearly as great as 8. One of the more external lymphatic glands of the groin. 9. A chain of four or five inguinal glands, which receive the thoracic duct. A valve the lymphatics from the genitals, abdomen, and external also exists at the mouth of

phena vein. 7. Efferent trunks from this gland; they

portion of the thigh.

this trunk, which has a similar arrangement and office with that of the left side.

The lymphatics have been asserted to be more numerous than the veins; by some, indeed, the proportion has been estimated at fourteen superficial lymphatics to one superficial vein; whence it has been deduced, that the capacity of the lymphatic is greater than that of the venous system. This must be mere matter of conjecture. The same may be said of the speculations that have been indulged regarding the mode in which the lymphatic radicles arise,—whether by open mouths or by some spongy mediate body. The remarks made regarding the chylous radicles apply with equal force to the lymphatic.

It has been a matter of some interest to determine, whether the lymphatic vessels have other communications with the venous system than by the two trunks just described; or, whether, soon after their origin, they do not open into the neighbouring veins,—an opinion held by many of those, who believe in the doctrine of absorption by the lymphatics exclusively, to explain why absorbed matters are found in the veins. Several of the older, as well as more modern, anatomists, have professed this opinion; whilst it has been strenuously combated by Sömmering, Rudolphi,' and others. Vieussens affirmed, that, by means of injections, lymphatic vessels were distinctly seen originating from the minute arteries, and terminating in small veins. Sir William Blizard' asserts, that he twice observed lymphatics terminating directly in the iliac veins. Mr. Bracy Clarke3 found that the trunk of the lymphatic system of the horse had several openings into the lumbar veins. M. Ribes, by injecting the supra-hepatic veins, saw the substance of the injection enter the superficial lymphatics of the liver. M. Alard' considers that the lymphatic and venous systems communicate at their origins. Vincent Fohmann thinks, that the lymphatic vessels communicate directly with the veins, not only in the capillaries, but in the interior of the lymphatic glands. Lauth,' of Strasburg,-who went to Heidelberg to learn from Fohmann his plan of injecting,-announced the same facts in 1824. By this anatomical arrangement, Lauth explains how an injection, sent into the arteries, reaches the lymphatics, without being effused into the areolar tissue; the injection passing from the arteries into the veins, and thence, by a retrograde route, into the lymphatics. M. Béclard believed, that this communication exists at least in the interior of the lymphatic glands; and he supported his opinion by the fact, that in birds, in which these glands are wanting, and are replaced by plexuses, the lymphatic vessels in the plexuses are distinctly seen opening into the veins. Lippis has made these communications the

1 Grundriss der Physiologie, u. s. w., 2ter Band, 2te Abtheilung, s. 247, Berlin, 1828.

2 Physiological Observations on the Absorbent System of Vessels, Lond., 1787. 3 Rees's Cyclopedia, art. Anatomy, Veterinary. 4 Magendie, Précis, etc., ii. 238.

5 Du Siége et de la Nature des Maladies, ou nouvelles considérations touchant la véritable action du Système Absorbant, etc., Paris, 1821.

6 Ueber die Verbindung der Saugadern mit den Venen, Heidelb., 1821, und Das Saugadersystem der Wirbelthiere, Heft 1, Heidelb., 1824; and Mém. sur les communications des vaisseaux lymphatiques avec les veines, Liége, 1832.

7 Essai sur les Vaisseaux Lymphatiques, Strasbourg, 1824.

• Illustrazioni Fisiologiche, etc., Firenz., 1825.

subject of an express work. According to him, the most numerous exist between the lymphatic vessels of the abdomen, and the vena cava inferior and its branches. So numerous are they, that every vein receives a lymphatic vessel, and the sum of all would be sufficient to form several thoracic ducts. Opposite the second and third lumbar vertebræ, the lymphatic vessels are manifestly divided into two orders:-some ascending, and emptying themselves into the thoracic duct; others descending and opening into the renal vessels and pelves of the kidneys. Lippi admits the same arrangement, as regards the chyliferous vessels; and he adopts it to explain the promptitude with which drinks are evacuated by the urine.

Fig. 258.

Lymphatics.

Subsequent researches have not, in general, confirmed the statements of Lippi. G. Rossi,1 indeed, maintains, that the vessels, which Lippi took for lymphatics, were veins. It would appear, however, that when Rossi was in Paris, he was unable to demonstrate, when requested to do so by M. Breschet, the very things, that he had previously figured and described. Panizza, too, affirms, that no direct union or continuity between the venous capillaries and lymphatics has ever been made manifest to the eye, either in the human subject or the lower animals:2 and, on the whole, the observations of Lippi as to the alleged termination of lymphatics in various veins of the abdomen have generally been either rejected as erroneous or held to refer to deviations from the normal condition. It is proper to remark, however, that, recently, Dr. A. Nuhn, Prosector at Heidelberg, has maintained, that there is a regular communication between the abdominal lymphatics and veins, and describes three cases of the kind which fell under his own observation. In two of these the lymphatics opened into the renal veins; in the third into the vena cava. The article contains a good history of the views of different observers on the communication between the absorbents and veins.

We are perhaps justified in concluding with Panizza, that anatomy has not hitherto sucrent lymphatic vessels proceed- ceeded in determining, with physical certainty, Lymphatic glands. The arrows in what relation the sanguiferous and lymphatic systems stand to each other, at their extreme

ing towards thoracic duct. b, b.

indicate the direction in which the chyle passes.

1 Omodei's Annali Universali, Jan., 1826.

2 Osservazioni Antropo-zootomico-fisiologiche, Pavia, 1833; and Breschet's Système Lym phatique, Paris, 1836.

3 Quain's Human Anatomy, by Quain and Sharpey, Amer. edit., by Dr. Leidy, ii. 43, Philad., 1849.

4 Müller's Archiv. fur Anatomie, u. s. w., Heft 2, s. 173, Berlin, 1848.

ramifications. M. Magendie' conceives the most plausible view regarding the lymphatics to be:-that they arise by extremely fine roots in the substance of the membranes and areolar tissue, and in the parenchyma of organs, where they appear continuous with the final arterial ramifications; as it frequently happens, that an injection sent into an artery passes into the lymphatics of the part to which it is distributed. By some, they are described as commencing either in closely meshed networks, interspersed among

the blood vessels of the several tissues, or else in pointed closed tubes or processes, as shown in the marginal figure of the lymph and bloodvessels in a part of the tail of the tadpole;-the bloodvessels being denoted by the corpuscles in them. In this state, many of the extremities of the lymphatics appear to communicate with pointed or star-shaped cells; but this, according to Messrs. Kirkes and Paget, may be peculiar to the embryonic state, as no similar cells are seen in the adult; nor is there any appearance of the existence of cells for the elaboration of lymph, similar to those described as existing in the intestinal villi.

Fig. 259.

Bloodvessels and Lymphatics from the Tail of the
Tadpole.

The structure of the lymphatic vessels is like that of the lacteals. They have the same number and character of coats; the same crescentic valves or sphincters, occurring in pairs, and giving them the knotted and irregular appearance, for which they are remarkable;-every contraction indicating the presence of a pair of valves, or sphincter. The minutest lymphatics seem, however, to be destitute of valves: but they are discernible in those of less than one-third of a line in diameter, and have the same structure as those of the veins. In man, each lymphatic, before reaching the venous system, passes through a lymphatic gland or ganglion, formerly called a conglobate gland. These organs are extremely numerous; and in shape, structure, and probably in function, resemble entirely the mesenteric glands. They, therefore, do not demand distinct notice. They exist more particularly in the axillæ, neck, neighbourhood of the lower jaw, beneath the skin of the nape of the neck, in the groins, and pelvis in the neighbourhood of the great vessels. The connexion between the lymphatics and those

1 See, on both sides of this subject, Müller's Handbuch, u. s. w., Baly's translation, p. 273, Lond., 1838; and Weber's Hildebrandt's Handbuch der Anatomie, iii. 113, Braunschweig, 2 Précis, &c., ii. 194. 3 Manual of Physiology, Amer. edit., p. 205, Philad., 1849.

1831.

glands is the same as that between the chyliferous vessels and mesenteric glands.

M. Chaussier includes in the lymphatic system certain organs, whose uses in the economy are not manifest, the thymus gland, the thyroid, the supra-renal capsules, and perhaps the spleen. These he considers to be varieties of the same species, and terms them all glandiform ganglions.

The

The thymus gland is a body consisting of distinct lobes, situate at the upper and anterior part of the thorax behind the sternum. It has been considered to belong more particularly to fœtal existence, and will be investigated hereafter. The thyroid gland is, also, a lobated organ, situate at the anterior part of the neck beneath the skin and subcutaneous muscles, and resting on the anterior and inferior part of the larynx, and first rings of the trachea. It is formed of lobes, which subdivide into lobules and granula; is of a red, and at times yellow colour; and presents, internally, cells or vesicles, filled with a viscid and colourless or yellowish fluid. Collected on the point of a knife after incising the gland, it appears like weak solution of gum, and is almost devoid of the ropiness of white of egg. Put into common rectified spirit it seems to lose only a little water; becomes solid, but not opaque; and loses but little. The same effects result in the cells when the gland is boiled for a quarter of an hour: no apparent solution occurs. thyroid gland has no excretory duct; and, consequently, it is difficult to imagine its use. It is larger in the foetus than in the adult, and has been supposed to be, in some way, inservient to foetal existence. It continues, however, through life; receives large arteries, as well as a number of nerves and lymphatics, and hence, it has been supposed, fills some important office through the whole of existence. This, however, is conjectural. Mr. King' has affirmed, what had been already imagined by many, that the absorbent vessels of the thyroid convey its peculiar secretion to the great veins of the body. It is the seat of goitre or bronchocele, the swelled neck, Derbyshire neck, papas, &c., as it has been termed in different quarters of the globe, a singular affection, which is common at the base of lofty mountains in all parts of the world; and for the cure of which, we have a valuable remedy in iodine. The eutrophic agency of this drug is particularly exerted on the thyroid, and it affords an additional instance, to the many already known, of remedial agents exerting their properties upon a particular organ, without our being able, in the slightest degree, to account for the preference. Iodine stimulates, perhaps, the absorbent vessels of the gland to augmented action; it certainly modifies the nutrition of the organ; and the consequence is absorption of the morbid deposit. Lastly; the suprarenal or atrabiliary capsules or glands are small bodies in the abdomen, behind the peritoneum, and above each kidney, which are larger in the foetus than in the adult. The arteries distributed to them are of considerable size. These bodies consist of small sacs, with thick parenchymatous parietes; are lobular and granular,—the internal cavity being filled, according to Sir Everard Home, with a viscid fluid 1 Guy's Hospital Reports, i. 437, Lond., 1836, and Sir Astley Cooper, ibid., p. 448. 2 Lect, on Comp. Anat., v. 262, Lond., 1828.