ANATOMY.

140'

immediately after killing an animal, not onlv the lacteal, but alsothe lymphatic, vessels, in the abdomen and lower extremities, be-come distended with their natural lluids, the course of those lluidsbeing stopped by the ligature.

The lacteals, the lymphatic's, and the thoracic duct, havetheir coats thinner and" more pellucid than those of the blood-vessels. But though their coats are so thin, they are very strong,as we daily see on injecting them with mercury, since they resista column of that fluid, the weight of which would burst the blood-vessels. This thinness prevents our dividing them from one ano-ther, and thereby ascertaining their number, as we do those iffthe blood-vessels' But as the blood-vessels have a dense internalcoat to prevent transudation, we have reason to believe the lym-phatics have the same. And as the blood-vessels have a muscularcoat, which assi-ts in the circulation; so may the lymphatics.

In most animals, but particularly in man and quadrupeds, theIvmphatic vessels are full of Valves . These valves have beendescribed by the celebrated Nttck, Ruvsch, and others, and aremuch more frequent than in the common veins, and thence theselymphatics have sometimes been distinguished by the name ofvalvular lymphatic vessels. These valves are generally two innumber, of a semilunar shape, and the one sometimes much largerthan the other. In most parts of the body these pairs are so nu-merous, that there are three or four pair in an inch, hut sometimesthere is no more than one pair, and sometimes several inches ap-pear without a valve. They are less numerous in the thoracicduet than in the branches of the system; thence it might be sup-posed, that in proportion as we go from the trunk to the branches,we should find them in greater number: but this is not alwaystrue, for Mr. Hcwson observed them more numerous in the lym-phatic vessels of the thigh, than on those of the leg.

The lymphatic system, in different parts of its course, has theGlands^ called conglobate, or lymphatic. These glands are soplaced, that the vessels come in on one side, and pass out on theother, in their way to the thoracic duct. They are commonly ofan oval, though sometimes of a round form, and frequently some-what flattened^ and of various sizes, some being no larger than amillet seed, while others are almost an inch in diameter.

The lymphatics may be divided into two kinds, viz. superficial,and deep-seated.

The Superficial Lymphatics consist of the numerous ves-sels that lie between the skin and the muscles, and belong to thesurface of the body or the skin, and to the cellular membranewhich lies immediately under it. Numerous large branches ofthem can be readily enough discovered in the limbs of dropsicalsubjects. Many of them run upon the top of the fool; others aregenerally to be found just under the inner ancle. Bv means oftubeswhich have been introduced into two of them, the lymphaticshave been filled the whole length of the lower extremity. (SecPlate XVIII. Fig. 2.)

The Deep-seated Lymphatics arise from the glands andbody of the penis, and accompany the arteries into the lower partof the pelvis. lienee if venereal matter be absorbed by thesevessels, the constitution may be affected without our being awareof it. The lymphatic vessels of the testicle are numerous, andvery large for the size of this organ. They arise from its coats,from the body of the testicle, ami from the epididymis; and afterrunning along the spermatic cord, they terminate in the lumbarglands. In their course they have few communications with eachother. The lymphatics of the scrotum, which are also numerous,go chiefly (o the'glands of the groin, though some pass along withthose of the testicle to the lumbar glands.

Of the Lacteal Sac and Duct, asd Absorbent Vesselsof the Trunk.

(See Plate XVIII. Fig. 2.)

The Receptacle of the Chyle is a membranous bag, some-what pyriform, two-thirds of an inch long, one-third of an inchover in its largest part when collapsed ; situated on the first verte-bra of the loins to the right of the aorta, a little higher than theright emulgent artery, behind the right inferior muscle of thediaphragm. It is formed l>v fliC uni not three lubes; one fromunder the aorta, the second from the interstice of the aorta andeava, and the third from under the einulgenls of the right side.

’P.he Lacteal Sac, becoming gradually smaller towards itsVOL. I.—NO. 10.

upper pari, is contracted into a slender membranous pipe, of abouta line diameter, which is generally named the thoracie dint.This passes between the muscular appendices of the diaphragm,on the right of the aorta. It then mounts betwren the aoita andthe vena azygos as far as the fifth vertebra of the thorax, where itis hid by the azygos, as this vein rises forwards to join the de-scending or superior cava; after which the duet passes ohliquelvover to the left side, behind the a-sophagus, aorta deseeudctis,and the great curvature of the aorta, until it reaches the left carotidartery; behind which, on the left side of the (esophagus, it nunto the interstice ot the first ari'd second vertebra of the tlvorax,where it begins to separate fro\ji the carotid, stretching farther to-wards the let! internal jugular vein by a circular turn, who.e con-vex part is uppermost.

The Coats of the sac and duct are thin transparent membranes;from the inside of which, in the duet, ten or twelve small semi-lunar valves are produced, mo t commonly in pairs ; which are -o-situated as to allow the passage of liquors upwards onlv. This isthe most simple and common course , situation, and structure ofthe receptaculum chyli and thoracic duct; but there often exists-a variety in these parts, in different subjects.

The Lacteal Vessels, so called horn their comm onlv con-veying a fluid of the colour of milk, are found in two sets, "whichcommunicate with each other; the internal begin from the innersurface of the intestines, where each lacteal is at first formed, upon:the surface of the villi, by numerous small radiated branches, with-orifices destined to imbibe the nutritious fluid or chyle. Front,the cavity of the intestines, tiiese vessels pass obliquely throughtheir coats, uniting as they go, so as to form larger "branches.They follow the course of the arteries and the veins, and are dou-ble their number; one being situated on each side. The-e-brandies run on the outside of the gut to that part which is nextthe mesentery ; and, whilst they are yet upon the gut, they aresometimes ot a size sufficient to admit a small pipe, so that thehave been frequently injected with mercury in the human subject".And in man, as well as in different animals," the external set appearbetween the peritona’al and muscular coat, and commonly run fora considerable way in the same direction with the intestine. Fromthe intestines, they run along the mesentery and mesocolon, to-wards the spine; passing through the lacteals, in their wav to tiv;conglobate or mesenteric glands. These glands divide the Iacte-als into two regions: from the intestines to the glands these vesselsare called lactea primi generis; and from the glands to the Uiora- 'cie, duct, lactea secundi generis.

The lacteals of the Jejunum are larger and more numerousthan those of the ilium. Those of the small intestines, a- tlievrim uppn the mesentery, commonly accompany the superior, ormesenteric artery, and unite, as they proceed, into largerbranches; so that, by the time they arrive at- the root of the me-sentery, they are of a considerable size.. From the mesentericartery, they descend by the sides of the aorta, and open at last-into the thoracic duct: the lymphatics of the large intestines runsomewhat differently,

1 he Thoracic Duct, which receives the hmphatics and-lacteals', differs in its size in different subjects; but it is always-smaller in its middle than at its begirmiitg. Sometimes its lowerpart is still larger, and that enlargement lias been called reeeptacu-ium chyli. It is considerable in some quadrupeds, in turtle, andin fish; but many anatomists have denied that there is any paitof the thoracie duct, in the human subject, that deserves the nameof receptaculum, having never seen any thing like a pyriform bag-,as it has been described, but merely an enlargement, net unlikea varix, and that only in few subjects; it generally appears onlya little larger at its middle than at its ends. This lowercxtremitVof the thoracic duet is formed by the union of uvo or three verylarge trunks or lymphatic vessels.

The superficial lymphatics of the Lungs form a beautiful net-work, the larger branches running chiefly between the lobules, thesmaller passing over them ; and here, as’well as on the- liver, and.other parts, there are numerous valves, the-existence of which hasbeen denied by some authors, f rom the surface they pass to theroot of the lungs, and there they go through the bronchial glands-At this place they are joined by the "deep-seated absorbentswhich creep along the branches of the trachea, and likewise on.those of the pulmonary artery and vein.

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