y

U. S. DEPARTMENT OF AGBpCl^Ly^E,

BUREAU OF ANIMAL INDUSTRY.— C«cClar 193.- i

A. D. MELVIN, Chief of Bureau. «, . . «

THE REGIONAL LYMPH GLANDS OF FOOD-PRODUCING ANIMALS.

BY

JOHN S. BUCKLEY, Assistant in Pathology, Pathological Division,

AND

THOMAS CASTOR, Veterinary Inspector.

[Reprinted from the Twenty-seventh Annual Report of the Bureau of Animal Industry (1910).]

WASHINGTON: GOVERNMENT PRINTING OFFICE. 1912.

CONTENTS.

Page.

Deacription of the lymphatic system 371

The submaxillary lymph glands 376

The parotid lymph glands 378

The postpharyngeal lymph glands 379

The cervical lymph glands 380

The deep cervicals or supplementary cervical lymph glands 382

The axillary or brachial lymph glands 383

The psepectoral or inferior cervical lymph glands 383

The popliteal lymph glands 385

The ischial lymph glands 385

The precrural, kneefold, or external subiliac lymph gland 385

Flank lymph glands 387

The superficial inguinal and supramammary lymph glands 387

The internal or deep inguinal lymph glands - 388

The sacral lymph glands 388

The external iliac or circumflex iliac lymph glands 389

The internal iliac lymph glands 389

The anal lymph glands 389

The sublumbar lymph glands 389

The renal lymph glands 390

The gastric lymph glands 390

The mesenteric lymph glands 390

The splenic lymph glands 392

The hepatic or portal lymph glands 393

The superior thoracic or subdorsal lymph glands 393

The inferior thoracic or suprasternal lymph glands 394

The lymph glands of the thoracic viscera 895

Other lymphatic structures 399

ILLUSTRATIONS.

PLATES.

Page.

Plate XXX. Lymph glands in the cow 376

XXXI. Lymph glands in the hog 380

XXXII. Lymph glands in the sheep 386

FIGURES.

Fig. 27. Head of cow, with tongue cut out 377

28. Head of hog, showing lymph glands 378

29. Left fore quarter of heifer, with exposed prescapular lymph gland 381

30. Portion of left thoracic wall of heifer 384

31. Left hind quarter of steer, exterior view 386

32. Left hind quarter of bull, internal view - 387

33. Stomach and portion of intestinal canal of hog 391

34. Gastric surface of the liver of cattle 392

35. Intestinal canal of cattle, spread out 393

36. Arteries and lymph glands of the intestines in the hog 394

37. Lungs and heart of steer, suspended, dorsal view 396

38. Lungs of hog, showing attached lymph glands 397

n

Historic, archived document

Do not assume content reflects current scientific knowledge, policies, or practices.

THE REGIONAL LYMPH GLANDS OF FOOD-PRODUCING

ANIMALS.

By John S. Buckley, D. V. S., Assistant in Pathology, Pathological Division,

AND

Thomas Castor, V. M. D., Veterinary Inspector, Philadelphia, Pa.

This paper dealing with the topographical anatomy of the lym- phatic apparatus of food-producing animals has been written in an endeavor to meet a need that must be felt by practically every be- ginner in that branch of sanitary hygiene which has to do with the examination of meats and the organs or carcasses of meat-producing animals. It is regrettable that a more absolute knowledge does not exist of the anatomical detail of this system in the various food animals, but an endeavor has been made to supply as much ag possible of the general knowledge that could be gleaned from the various works that treat of this subject, together with a fair amount of orig- inal investigation carried out by the writers of this paper.

Hitherto no great amount of special attention has been devoted in the veterinary schools to the study of the lymphatic system, but the prominence which has lately been given to the inspection of meats and carcasses of meat-producing animals necessitates a closer ac- quaintance with all that pertains to these structures, as intelligent judgment as to the fitness or unfitness of meats for human consump- tion is based largely on the conditions found in the lymph glands. As it is in the diseased carcasses that we find presented the ideal conditions for the best appreciation of the whole lymphatic appa- ratus, to the novice in meat inspection an exceptional opportunity is there afforded for its study which should on no account be neg- lected.

DESCRIPTION OF THE LYMPHATIC SYSTEM.

The lymphatic system presents for study the lymph and its cellular constituents, the lymph vessels and lymph glands, together with cer- tain accessory lymphatic structures which form a part of the system.

THE LYMPH.

The lymph itself is identical with the plasma of the blood and con- tains cellular elements which vary much at different periods and in different parts of the animals at the same time. In the intercellular lymph spaces and in the finest lymph radicles it has a poor cellular

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372 KEPOBT, BUREAU OF ANIMAL, INDUSTRY.

content, while it possesses rich cellular contents as it leaves the lymph glands. These cellular elements are variously classified by different histologists, one of the most convenient classifications being that based on their size, form of nucleus, and structure, into large lymphocytes, small lymphocytes, polynuclear leucocytes, and transitional leucocytes. According to their granules and their staining characters they are classified as eosinophiles (or oxyphiles), basophiles, and neutrophiles.

THE LYMPH VESSELS.

Looking at the lymphatic apparatus in a normal healthy individual, we find it to be made up of a system of tubes or conduits, sometimes designated the white blood vessels, beginning as terminal culs-de-sac in the tissue interspaces, coursing as intricate and extensive networks in practically all tissues excepting muscles bundles (but they do not exist in the intermuscular sheaths) , nerves, and blood vessels, and terminating finally as two large lymph vessels known as the thoracic duct and the great lymphatic vein, which empty into the blood vas- cular system near the junction of the jugular veins in the anterior vena cava.

Within the lymph vessels are situated involutions of the endo- thelial lining, forming valves which correspond to the valves of the veins, these valves being much more numerous, though, than in the veins. The smallest lymph vessels, i. e., the lymph capillaries, do not contain valves, nor are valves at all numerous in the thoracic duct, although several do exist at its juncture with the veins, these forming a contrivance to prevent passage of blood backward into the thoracic duct. But in all the vessels of an intermediate size the valves may readily be seen in injected preparations as constricted nodes about one-sixth of an inch apart.

In many respects the lymph vessels simulate the veins of the blood vascular system both in structure and function. They are, in fact, adjuncts of that system.

The capillary lymph vessels are formed by a single layer of endo- thelial cells, as are the smallest of the blood capillaries, and according to late investigations are said to have their origin in closed terminal culs-de-sac instead of open intercellular lacunar spaces.

Aside from the possession of valves, the intermediate and large lymph vessels are made up of three coats, as are the veins (an inner endothelial, a middle muscular, and an outer connective tissue envel- ope)., and are said to divide about equally with the veins the absorb- ent functions. It is to be noted that those lymph channels of large size also possess elastic fibers, these acting in a mild degree for the impelling of the lymph onward toward the blood.

The lymph collected by the lymphatics from all parts of the body is finally emptied into the blood stream through the agency of the

LYMPH GLANDS OF FOOD-PBODtTCING ANIMALS.

373

two large vessels already mentioned the thoracic duct and the great lymphatic vein.

The thoracic duct has its origin in a very irregularly shaped cystic dilation known as the reservoir of Pecquet, or the receptaculum chyli, situated beneath the first lumbar vertebra near the adrenals. From this origin it extends forward through the diaphragm (in cattle by a special opening) , passing along the lower surface of the dorsal vertebrae and above the aorta to the apex of the thorax, and empties into the anterior vena cava. This duct receives the lymph from all parts of the body except from the right fore limb and the right half of the head, neck, and thorax. The thoracic duct is some- times double throughout its extent, originating in the one reservoir and emptying at the junction of the two jugulars.

The great lymphatic vein, or the right lymphatic vein, is an extremely short trunk which receives the lymph from the right side of the head, neck, thorax, and right fore limb and empties into the venous system at the junction of the jugular veins or anastamoses with the thoracic duct just above the point of juncture with the anterior vena cava. It is formed by the efferents of the prepectoral glands of the right side.

THE GLANDS.

On the course of the lymph vessels are interpolated adenoid structures called lymph glands. The glands are nodular organs, varying in size from almost imperceptible points to that of a hen's egg, and varying also as regards the species of animals. In form they may be flattened, round, cylindrical, or reniform. Usually, though, they are more or less reniform (i. e., kidney shaped). The lymph vessels approaching a gland enter, after breaking up into many branches, in an oblique direction on its convex border and are known as the afferent vessels. These are the conduits that convey the lymph directly from the various tissues to the respective or cor- responding lymph glands. After having traversed a complex laby- rinth of channels in the gland and having its composition altered both chemically and histologically, the lymph leaves the gland by the efferent lymph vessels which have their origin at the hilus of the gland, situated on its concave border. These efferent vessels either enter into another gland or pass directly to the receptaculum chyli, the thoracic duct, or the right lymphatic vein.

An idea of the structure of a gland may be gotten from a study of the lymph follicles in the walls of the intestines, and then of a plexus of lymph vessels, within the meshes of which are jilaced these simpli- fied collections of germinating lymphatic cellular elements.

A lymph follicle as found in the intestinal mucosa is nothing more than a small round aggregation of proliferating lymph cells held in

374 27th eepoet, bueeau of animal industey.

an extremely delicate stroma of adenoid connective tissue and pene- trated by a richly arborescent capillary arterial twig which furnishes it nutriment. Surrounding some of these aggregations of lymphatic cellular elements is an extremely delicate connective tissue capsule opening into and continuous with the surrounding lymph capillaries, much on the order of a Bowman's capsule covering a Malpighian corpuscle in the kidney.

The lymph gland might be considered to be nothing more nor less than a large collection of these simple lymph follicles held together by a connective tissue framework containing trabeculse which sepa- rate the follicles and surrounded by a thick capsule from which this framework takes its origin. Intermixed with the fibers of connective tissue are involuntary muscle fibers in the lymph glands of some of the lower animals. The individual follicles of this compound gland do not completely fill the alveoli formed by the trabecular frame- work, but are surrounded in each instance by a hollow space which corresponds to the space between the capsule mentioned above as surrounding a solitary follicle and the follicle itself. In the com- pound lymph gland these spaces are all continuous with one an- other toward the medullary portion of the gland. The follicles of the medullary portion are elongated structures and are known as the medullar}' cords. The intercommunicating follicular lymph spaces finally are continuous with the efferent lymph vessels of the gland. For convenience of description the structure of the lymph glands is usually described as being divided into a cortical and medullary por- tion, the only difference in the two being in the shape of the lymph adenoid structures, those in the cortical portion being round and called cortical follicles, and those in the medullary portion being elongated and known as medullary cords. The spaces surrounding the follicles and cords are known as the lymph sinuses, and it is through the sinuses that the lymph passes on its way from the afferent to the efferent lymph canals. It is while traversing these tortuous sinuses that the lymph is altered in composition. From a meat-inspection standpoint it is well to remember that foreign and deleterious matter that has been taken up by the lymph on its pas- sage through the different tissues is oftentimes removed or destroyed either by a process of filtration or by chemical counteraction. This function of the gland is very important, as certain deleterious sub- stances— such, for instance, as infectious micro-organisms (tubercle bacilli for a specific example) if emptied unceremoniously by the lymphatics into the blood stream would probably be distributed over the whole organism and would likely set up a generalized infection a septicemia which would most probably soon terminate in death. The lungs, of course, filter out many germs that are thus emptied into the blood streams.

LYMPH GLANDS OF POOD-PKODUCING ANIMALS.

3V5

The bacteria filtered out or retained temporarily by lymph glands are often destroyed and disintegrated. However, such is not always the case, and bacteria may even pass through a lymph gland without leaving any trace of their passage. Many of the bacteria which are retained are chemically treated and disintegrated, or, not being de- stroyed, they produce disease of the glands. Other substances, such as particles of carbon, are filtered out and may be readily seen in the bronchial glands of nearly all old animals. Blood and other tissue pigments are seen in the glands where there has been a destruction of these tissues upstream. Parasites, too, are at times found in these structures.

The lymph as it leaves the gland is much altered. It is in the gland that some of the lymph corpuscles, which play such an ex- tremely important part in the protection of the body from infections and injuries, are added to it. It is while thus passing through that the lymph acquires its property of coagulability, i. e., it receives its fibrinogenetic qualities. The lymph with its new qualities and new constituents, together with its load of modified waste from the tis- sues, is now ready to be emptied into the blood stream to be passed along to the excretory organs.

The statement that the lymph glands filter out and modify dele- terious matters could not be very readily demonstrated by simple macroscopic means in a young, healthy animal, but it is clearly exemplified in cases of infections of individual organs and regions and in old animals where pigmentation of these glands is often observed. It is on such findings that the meat inspector is most often obliged to depend for basing his opinion of health or disease, and for deciding localization and generalization of disease and the fitness or the unfitness of meat for food purposes.

If the lymphatic system is the " scavenger of the body," if it pro- tects the body from disease, it also furnishes a route of entry for disease, and in certain cases acts as a disseminator of disease. Those cancerous atlections and infectious diseases of a malignant character which have by intent or chance become inoculated into the body are not long held in abeyance by the lymph glands, for the lymph conduits act as ways of transport in such cases, to the detriment of the whole body.

In consistency and color the lymph glands vary much. In young, rapidly growing animals the glands are quite prominent and juicy; in old and mature animals they are more firm and compact. Some- times in old milch cows the lymph glands may be quite prominent, but are usually fibrous in texture. The splanchnic lymph glands are softer in structure than those in other parts of the body, those of the abdominal digestive organs being more juicy, especially during absorption from the intestines.

376 27th ebpokt, bureau of animal industry.

The interior parts of the mesenteric glands are usually darker in color than those of other regions. The colors that prevail are white, light gray, dark gray, mottled gray and brown, light brown, and sometimes red or even black.

The red lymph glands usually represent a special kind of gland known as hemo-lymph glands, the color being due to the presence of red blood cells in the sinuses. These are quite normal glands, and are thought by some to be transitional forms, or forms induced by alterations in other organs, especially the spleen, and by others are supposed to relieve the spleen of a part of its function in the metabolism of the blood. These small red glands usually occupy a position in the sublumbar region and are designated by Warthin as " spleenolymph glands " and " marrowlymph glands."

Black lymph glands, or mottled black and white, while not nor- mal, can not be said to be always really diseased, since the color may be due to a mere deposition of normal pigment or to carbon particles which have no special significance, at least from a meat- inspection standpoint. The cortical portions of many lymph glands are white or light gray, while the medullary portions are rather dark in color. In many old animals the lymph glands are quite fibrous in texture, and on section are of a yellowish-white color.

Although the routes of the lymph conduits are more or less con- stant, there may easily be diversions of the normal or usual flow of lymph, due to various causes, the most important of these being the retrograde movements, due to blocking of the lymph channels in disease, as in cancerous and other conditions. Anastomoses of lymph vessels of adjacent regions may occur, as in inflammatory adhesions of one lobe of the lung with an adjacent lobe, or adhesion between the visceral and parietal or the visceral and mediastinal pleura, etc. All such points must constantly be kept in mind in order to render intelligent judgment in a seemingly unexplainable finding.

THE SUBMAXILLARY LYMPH GLANDS.

The submaxillary lymph glands in cattle are located superficially in the lower portion of the inferior maxillary space, between the inner aspect of the inferior maxillary bone and the submaxillary salivary glands, about 2 inches anterior to the point where the lower border of the inferior maxillary bone curves abruptly upward and above the anterior attachment of the sterno-maxillaris muscle. Usually there is but one node on each side, but at times there are two glands lying very close to each other. (See PI. XXX, 4, and fig. 27, h.)

In hogs, these glands lie, covered by the salivary glands, more pos- terior than in cattle. (See fig. 28, 9.)

Their afferent vessels, chiefly superficial, are derived from the mucous membrane of the anterior nares, the muscles of the lips,

LYMPH GLANDS IN THE COW.

1, Parotid lymph gland; 2, atlantal lymph gland, or the most superior of the superior cervicallymph glands; 3, postpharyngeal lymph gland; 4, submaxillary lymph gland; 6, small glands on the median portion of the superior face of the trachea; 6, prescapular lymph gland; 7, S, 9, prepectoral lymph glands; 11, inferior thoracic or suprastemallymph glands situated along the course of the internal thoracic artery and vein; 12, sterno-diaphragmatic lymph gland; 13, superior thoracic or sub- dorsal lymph glands; U, chain of lymph glands in the posterior mediastinal region; 13, lymph nodes along the inferior surface of trachea in the anterior mediastinal space; 16, posterior bronchial lymph gland, under the bifurcation of the trachea; 17, sublumbar lymph glands, at vcp the most anterior are at the origin of the celiac arteries; IS, external iliac or circumflex iliac lymph glands, at the angle of the haunch: 19, external iliac lymph glands at the angle of the crural trunk; 20, popliteal lymph gland; 21, superficial inguinal or supramammary lymph glands. (From Auregglo's "Album Guide.")

LYMPH GIAND8 OF FOOD-PEODUOING ANIMALS.

377

cheeks, and tissues of the anterior maxillary space, and from the anterior portion of the tongue. The efferent or outgoing lymph vessels pass to the superior cervical lymph glands.

In cattle the head is often severed from the carcass without removing the tongue and is so inspected, and in this case the submaxillary lymph gland is reached by making a longitu- dinal incision just within the angle of the infe- rior maxilla along the inner border of the stemo-maxillaris muscle, when it will be found adjacent to the submaxillary salivary gland. In other cases the tongue is removed from the head and hung up by its tip, when the gland may very easily be' reached by grasping the side of the base of the tongue with one hand to draw the tissues tense, and then making one or more short transverse incisions to the inside of the sterno-maxillaris muscle and directly opposite to the arytenoid cartilage of the larynx. These incisions should cut directly through the submaxillary lymph gland, thus exposing it for inspection.

In hogs the method of reaching these glands T^aries with the method of slaughtering. In many of the smaller establishments where the killing is slow and the work of inspection is conducted by one inspector at the eviscerating bench, it is the custom to remove the liver, lungs, heart, and tongue without separating them, and in this case the submaxillary lymph glands may be easily removed from the carcass with the tongue if a good, wide incision is made and then both sets of glands may be readily located a short distance apart embedded in the fat on each side of the tongue ; but it is neces- sary to distinguish between the lymph glands and the salivary glands, which are also removed by this method and lie adjacent to the sub- maxillary lymph glands. In the larger estab- lishments where the killing is conducted very rapidly these glands are examined on the scraping or heading bench, the head being almost severed from the body by a free trans- verse incision at the throat, after which the glands may be readily found in the location previously described by 221280-Cir. 192—12 2

Fig

27. Head cow, with tongue cut out. a, a'. Postpharyngeal or retropharyngeal lymph glands ; b, submaxillary lymph glands ; c, ton- sils ; d, posterior nares ; f, submaxillary salivary gland ; g, styloid process of hyoid bone. (From Edelmann's " Meat Hy- giene.")

378

27TH EBPOBT, j^TJKEAU OP ANIMAL INDtrSTET.

making a longitudinal incision through the salivary gland and into the adjoining submaxillary lymph glands, thus exposing them for inspection. Some inspectors use a small hook with which the salivary gland is drawn outward and twisted slightly, thus allowing the ad- joining lymph glands to be exposed easily and rapidly with a small incision. Experience is necessary to locate them rapidly and accu- rately, so as not to delay ot hinder the killing operations.

THE PAROTID LYMPH GLAND.

In cattle the parotid lymph gland is located at the supero-anterior border of the parotid salivary gland, being partly embedded in the same and partly lying on the masseter muscles about 1 inch in front

of and a little lower than the external meatus of the ear. (See PI. XXX, 1.)

In hogs the parotid glands, very numerous, large, and red in color, are arranged in a chain along the anterior border of the parotid salivary gland and posterior to the border of the inferior maxillary bone. (See fig. 28, 1 and 1'.) On the killing beds it will be noticed that very often one or more of them are left intact on the inner surface of the jowl after the head is re- moved in that method

•Fig. 28. Head ot hog, showing lymph glands. 1. 1'. Parotid lymph glands ; 2, postpharyngeal or retro- pharyngeal lymph glands ; 3, 3', superior cervical lymph glands ; 8, submaxillary salivary glands ; 9, submaxillary lymph gland on each side of the salivary gland in the Intermaxillary space. (From Aureggio's "Album Guide.")

of slaughter where the jowls are allowed to remain attached to the carcass. Where the jowls are removed from the carcass with the head, as is done in many of the larger slaughterhouses, these glands may often be easily seen, as they are frequently cut through when the head is severed from the body, although in some cases they may be entirely removed with the head and jowls, or in others they may remain in the carcass, depending entirely whether the head is cut off long or short.

The afferent vessels, chiefly of the deep variety of lymphatics, are derived from the anterior and lateral portions of the head and from the temporal and parotid regions, the cranial cavity, the base of the cranium, the tongue, the soft palate, the esophagus, and the larynx. The efferent vessels pass to the superior cervical lymph glands.

LYMPH GLANDS OP rOOD-PBODUCING ANIMALS.

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THE POSTPHARYNGEAL LYMPH GLANDS.

The postpharyngeal or retropharyngeal lymph glands are located in cattle at the base of the cranium just superior to the pharynx, lying close on either side of the median line between the branches of the hyoid bone. (See PI. XXX, 3, and fig. 27, a and a'.) These glands consist of two quite large nodes, one on each side.

In hogs they are usually quite small and are situated more pos- terior than in cattle, on the lateral plane of the larynx and the pharynx at about the lower end of the styloid process of the occipital bone. (Seefig. 28, 2, andPl. XXXI, 24.)

They receive lymph radicles from the posterior nares, the cranial cavity, the posterior portion of the oral cavity, the tonsillar region, and the pharynx, also from the other lymph glands of the head. The tonsils, in cattle at least, have four or five large ducts that empty directly into the postpharyngeal glands.

The efferent lymph vessels pass to the other superior cervical glands that lie above the pharynx but more posterior and external to the hyoid bone the parapharyngeal glands after which they pass down along the trachea following the carotid artery to the mid- dle cervical glands.

It will readily be seen how very important these glands are, from a meat-inspection standpoint, as they receive most of the efferent lymph radicles of the entrance to both the digestive and the respira- tory tracts. Indeed, it is a matter of fact that these glands are often the very first to show tubercular infection. And, too, those animals affected with actinomycosis that have the postpharyngeal glands involved usually show nodules of actinomycotic growth in the lungs. This would appear to indicate that the lymphatics are not always a protective factor in disease, but in this case their effer- ents possibly furnish a route by which this disease soon gains entrance to the blood and is filtered out in the lungs.

These glands may be exposed in cattle as follows : Where they are examined in the head after its removal from the carcass, but before the tongue is cut out, draw the larynx downward with the hand (or upward and forward when the head is lying face downward, as is 'ordinarily the case), then make a free transverse incision near the base of the cranium, which will reveal the glands lying on the supero-poste'rior surface of the pharynx. If the tongue has been cut out and hung up by its tip, it is a very simple matter to examine the glands as they are exposed to view on the wall of the pharynx at the superior part of the base of the tongue. When the pharynx is not opened up longitudinally they lie almost adjoining each other in the median line, whereas if it is opened, as it should be, to clean it of particles of food, mucus, etc., the glands will drop somewhat one to each side ^but hanging in full view at the level of the anterior

380 2,lTU EEPOKT, BUBEAU OP ANIMAL INDUSTRY.

border of the arytenoid cartilage. This position will of course vary somewhat when the tongue is hung up by its base, as is sometimes done.

In hogs the method of locating these glands is similar to that de- scribed for the submaxillary glands, the only difference being the slight difference in location, the postpharyngeal being located in a mass of fat at each side of the larynx and pharynx, and not so large or prominent as the submaxillary glands.

THE CERVICAL LYMPH GLANDS.

The term " cervical lymph glands," as used in the meat-inspection regulations and reports of the Bureau of Animal Industry, includes the submaxillary, the superior cervical, the postpharyngeal, the para- pharyngeal, and the parotid lymph glands. These are very impor- tant to the inspector, and it is necessary to examine them carefully. In hogs especially the cervical lymph glands frequently present the first and often the only lesions of tuberculosis found in the entire carcass.

When tuberculous lesions are found in any of the cervical lymph glands in a carcass that is to be passed for food or lard, the head and tongue should be condemned and tanked^ or may be passed for lard, depending upon the extent and severity of the lesions, but if passed for lard all the cervical lymph glands should be carefully trimmed out, and in either case all of the lymph glands of the neck region, including the prepectoral, the prescapular, the middle cervical, and the deep or supplementary cervical glands, should be thoroughly trimmed out and tanked.

THE SUPERIOR CERVICAL LYMPH GLANDS (aTLANTAL, PARAPHARYNGEAL, AND ANTERIOR CERVICALS).

These glands are located in cattle at the extreme superior end of the submaxillary salivary gland, just under the styloid process of the occipital bone, and bordering the lateral aspect of the occipito-atloid articulation just above the pharynx. They consist of a small group, two or three in number. (See PI. XXX, 2, and PI. XXXII, 7'.)

The superior cervical glands in hogs are very important ones to examine for tubercular infection. See also the middle cervicals, which are continuous with these in the hog. (See PI. XXXI, 23, and fig. 28, 3 and 3'.)

They receive afferent vessels from the immediate surrounding tis- sues, and the efferent branches from the three preceding glands. Their efferents pass, accompanying the large blood vessels lying be- side the trachea, to the inferior cervical glands, at times directly, at times through one of the small glands, interposed on their course, known as the middle cervicals.

1, Incision to expose the gland of the hock; 2, popliteal lymph gland; 3, anal lymph gland; 5, superficial ingninal lymph gland; 6, internal obturator muscle: 7, ischial lymph gland; 8, posterior node of the internal iliac lymph glands; 9, subsacral lymph glands; 10, incision to expose the external Inguinal lymph glands; 11, group of lymph glands in the sublumbar region, continuous with the internal iliacs; 13, suDlumbar lymph nodes; 14, kidney; 16ff, stemo-diaphragmatio lymph gland; IS, small lymph nodes along the aorta; 19, inferior thoracic or suprasternal lymph gland; 21, prepeetoral Ivmph glands; 23. glands of the median cervical region, seen osnallj still attached to the dressed carcass; 24, postpharyngeal or letropharyngeal lymph glands. (From Aureggio's "Album Guide.")

LYMPH GLANI« OP FOOD-PRODUCIirG ANIMALS, 381

THE MIDDLE CERVICAL LYMPH GLANDS.

These are small glands, several on each side, against the wall of the trachea and esophagus, just a little lower than the thyroid gland. (See PI. XXX, 5.) Large nodes are never present except occasion- ally in the sheep. It will be found that the efferent lymph vessels of the superior cervical glands pass through the nodes that may be present. These glands receive afferent radicles from the esophagus and the trachea. Their efferents pass directly to the prepectoral Ijrmph glands. In hogs these glands are continuous with the superior cervical chain which extends upward to the occipital bone. (See PI. XXXI, 23.) In cattle they are often absent.

Fig. 20. Left fore qmirter of heifer, with exposed prescapular lymph gland, a, 9, Cervical trapezius muscle ; h, 6', omo- tr^srersarlug moscle ; c, c", c"> brachiocephalic muscle ; b, pre- scapular lymph gland. (From Edelmann's "Meat Hygiene.")

THE .PaBSCAPTJtAR OR StrPERTICIAL CERVICAL LYMPH GLANDS.

These glands are located a little above and inward from the shoul- der joint, embedded in a cushion of fat and covered by the mastoido- humeralis muscle. This gland in cattle consists of an elongated voluminous glandular node (see PI. XXX, 6, and fig. 29, 1) ; in hogs, a more or less completely fused chain. They play an important part in deciding the question of generalization of disease in tubercu- losis, for example -as the afferents are all derived from centripetal lymph ducts, i. e., from ducts that are not connected with any other lymph area. In other words, this lymph area is an isolated area, so that any secondary infection coming in it must first be brought to this area through the medium of the blood vessels. Perhaps inflam- matory conditions which would cause anastomoses with the lymph

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vessels of an adjoining region might take place. In this manner pleural lymph radicles could become fused with deep-lying lymph vessels on the pectoral wall, and these in turn pass over the shoulder to the prescapular glands. It would seem that such a roundabout course would almost never take place. Of course disease of these glands without other centers of infection would point to a primary local infection.

The afferent radicles are derived from the superficial parts of the shoulder, the upper and lower leg, the posterior portion of the lateral pectoral wall (the vessel in this latter case passing to these glands across the muscles of the shoulder) , from the superficial parts of the base of the neck, and from part of the inner face of the scapular region.

The efferent vessels pass to the prepectoral lymph glands, i. e., the inferior cervicals.

The glands may usually be felt in live cattle by pressing the hand forcibly in the hollow of the shoulder, about in front of the neck of the scapula. In a side of beef in the hanging position a small cut parallel to the muscle fibers along the superior border of the mas- toido-humeralis muscle, 3 inches in length, just inward from the shoulder joint, will be sufficient for the inspector to reach in and secure the gland for examination. The muscle can then be laid back in place, flattened out with the hand, and held there with a skewer, so that when the carcass cools it will be scarcely possible to notice any sign of the muscle having been disturbed. It may also be reached for examination from the inner surface of the split beef car- cass by making a longitudinal incision through the neck muscles in the jugular gutter just anterior to the scapulo-humeral articulation. This method is preferred by many inspectors.

In hogs it is easiest reached from the internal or split surface of the carcass by making a transverse cut just in front of the shoulder joint from the nape of the neck to the trachea some distance anterior to the first rib, and the lymph gland will be found to occupy a place about in the middle of the incision.

It is also quite important to examine these glands in sheep to detect diseases such as caseous lymphadenitis. In sheep the glands are located as in cattle. (See PI. XXXII, 9.)

This gland, like the other bond glands, is, as a rale, only exam- ined in the final examination of retained carcasses, as to expose them mutilates the carcass more or less.

THE DEEP CERVICALS OR STrPPr.EMENTARy CERVICAL LYMPH GLANDS.

These glands are located, in hogs, above the superficial cervical glands beneath the angular muscle of the scapula, external to the lower part of the second cervical vertebra, embedded in a mass of fat.

LYMPH GLANDS OF FOOD-PEODTJCING ANIMALS.

383

The afferent vessels are from the deep muscular layers of the base of the neck. The efferent vessels pass to the superficial cervical or prescapular gland.

In cattle this gland does not exist.

This gland can be reached in the hog after the carcass has been split by cutting through the neck muscles inferior to the first and second cervical vertebrae. To reach the gland in this manner muti- lates the neck somewhat and occasionally the shoulder to a slight extent. A still better way as it causes very little mutilation is, in the hanging, split decapitated carcass to make a free upward incision between the neck muscles covering the first and second cer- vical vertebra} and the layer of superficial fat, when the gland can be readily reached in a cushion of fat somewhat anterior to the scapula and torn loose and brought out for examination.

This gland is considered in the work of the Bureau of Animal Industry as a portion of the prescapular glands and should be so named in making out reports.

In the superficial parts of the base of the neck and shoulder there are also several other very small lymph nodes.

THE AXILLARY OR BRACHIAL LYMPH GLANDS.

These glands are located in cattle on the inner aspect of the inter- nal scapular muscles, posterior to the shoulder joint, in the midst of the brachial vessels and nerves where these emerge from the thorax and enter the leg. They are variable in number and usually are smaller and more flattened than any of the glands so far described.

The axillary lymph glands are most often missing in swine, and the lymph of this region empties into the median or inferior cervicals.

The gland is accessible only from the external surface after remov- ing the scapula, which is ordinarily impracticable in a food carcass, but may be easily reached in cattle from the inrier surface of tlie split carcass, as it lies just external to the first or second rib (usually the latter) at about midway between its two extremities ; and by cutting through the miiscles along the anterior border of the first rib near its center the gland may be readily located embedded in a cushion of fat external to the first or second rib. This gland is not examined in the ordinary post-mortem meat inspection.

They receive their afferent rootlets from the middle and inner scapular region, from the lower arm, forearm, and foot, and from the thoracic walls. Their efferent vessels pass to the prepectoral or inferior cervical glands.

THE PREPECTORAL OR INFERIOR CERVICAL LYMPH GLANDS.

In cattle and hogs these glands are located at the entrance to the thorax on and between the lower anterior borders of the two first ribs laterally and inferior to the trachea and esophagus, extending

into the fore part of the anterior mediastinum, usually embedded in fat that also acts as a cushion for the large veins and arteries at this location. (See PI. XXX, 7, 8, 9; PI. XXXI, 21, and fig. 30, 5.)

These are very important glands to examine, as they are the terminal glands through which all the lymph from the head, neck,

and fore extremities passes on its way to the thoracic duct and the right lymph vein. They also re- ceive the efferents of the suprasternal lymph glands o n their passage to the thoracic duct and from several small lymph nodes in the anterior mediastinal space. They bear the same relation to the anterior portion of the body as do the sublumbar glands to the vessels of the posterior regions. The efferents of the prepectoral glands on the right side empty into the great lymphatic vein, and on the left side into the thoracic duct or occasionally into the anterior vena cava. These glands are frequently found to be affected with tu- berculosis, so occa- sionally lesions of that disease may be thus detected even after the viscera have been removed and disposed of. ^ ^ese glands, or at least a Jwrtion of them which always remain in the hanging split carcass of beef, may be easily reached by insert- ing the knife into the cut end of the large venous trunk above re- ferred to and making a downward longitudinal incision parallel to the fibers of the long muscles of the neck, where the gland may be readUv found embedded a short distance in the fatty cushion.

'Pia. 80. Portion of left thoracic wall of heifer. A, Inter- nal thoracic artery ; Vi Internal thoracic vein ; M, tri- angular muscle of the sternum cut through ; a, inferior thoracic lymph glands ; a', anterior mediastinal lymph glands ; b. Inferior cervical or prepectoral lymph glands. (From Edelmann'B " Meat Hygiene.">

LYMPH GLANDS OF FOOD-PBODtTClNG ANIMALS. 385

Proceeding somewhat in the order of examination of the carcass as it is conducted at the time of evisceration, or following the plan of inspection by passing from terminal to central lymph structures as the lymph flows, we have the following glands :

THE POPLITEAL LYMPH GLANDS.

The popliteal lymph glands are located deep in the muscles behind the knee joint on the gastrocnemius between the semitendinosus and biceps femoris muscles at about the point of bifurcation of the gas- trocnemius. (See PI. XXX, 20, and PI. XXXII, 1, 1'.)

In hogs the popliteals are absent in some instances, but there exists always a very small gland in the subcutaneous tissues 3 or 4 inches above the hock. (See PI. XXXI, 1, 2.)

The popliteal gland is not examined ordinarily, this not being con- sidered necessary except in special cases, as it mutilates the carcass considerably to expose it. To reach it in the hanging cattle carcass, make an incision on the posterior part of the thigh, parallel to the muscle fibers, between the biceps femoris and the semitendinosus muscles, on a line from the point of the ischium to the point' of the OS calcis, at the intersection of a horizontal line drawn backward from the center of the patella. The fingers may then be thrust in between the muscles to the cushion of fat between the heads of the gas- trocnemius, where the gland may be readily located.

The afferent vessels are from the lower portion of the hind leg. The efferent vessels follow the sciatic nerve, pass upward to a lymph gland (the ischial) lying on the outer portion of the ischium in the middle of the lesser ischiatic notch, thence to the posterior sublumbar gland. At times they pass by this gland without entering it and pass directly to the sacral or sublumbars or the internal iliacs.

THE ISCHIAL LYMPH GLANDS.

These glands are located on the deepest and outer part of the lesser ischiatic notch, adjacent to the external surface of the bone, covered by the broad ligament of the pelvis, on the ventral border of the coccygeal muscle. (See PI. XXXI, 7.)

The afferent vessels are derived from the surrounding region and from the efferent branches of the popliteal glands. Sometimes the efferents of the popliteals pass quite near to this gland without enter- ing it.

The efferent vessels of this gland pass to the sacral and sublumbar glands.

THE PRECRURAL, KNEEFOLD, OR EXTERNAL SUBILIAC LYMPH

GLAND.

This gland forms a voluminous mass located in the loose cellular tissue of the flank just above and inward from the femero-tibial articulation on the anterior border of the tensor fascia lata muscle.

flTS BBP08T, BtTBEAtT OP ANIMAL INDtlSTBY.

(See PI. XXXI, 10, and fig. 31, I)

,Fie. 31. -Ititt blndaiutrter of tteer, external ylew.

teal iTiniili gland; I, precraral Ijmph gland; h, i', biceps fw<H^l8 muaele; e, BemlmembranosuB muscle. (From Edel- mann'B " Meat Hygiene.")

gland can be readily found with the least

In animals in good condition it is embedded in a mass of fat. It is one of the most ac- cessible glands , in the dressed carcass, and is quite as im- portant from the meat- inspection standpoint as is the prescapulai