FTVE F'IGTIILES In a recent paper ('34) the writer establishet2 the presence of omcntal lymphatics in tlie white r a t and in man. Thcl occurrciice of similar chaiiriels in other species has long heen an open qnestion which has aroused great intercst. This investigation afforcls a dcfiiiitc aiiswer t o the problem iu so fat. as the dog atid cat are coiicerned, and it demonstrates the p a t h of lymph drainage in these animals from the omental vessels t o the thoracic duct. REV T I 3 W O F LI 'I'ER AT LlR 13: Numerous investigators have studied the ommtum of the dog. Robinson (189<5)discnssetl its macroscopic anatorny and conchided that this organ is a great peritoiical protcctor against infectious discilses. A fcw p a r s later I-7cger ('04) iiitroilucd metallic powde1- into the peritoneal cavity and studied its movement by ineaiis of tlie X - r i l j T . R e belicved that granulrs of particnlatc matter entered the lymph vesscls of the omcritum aud wem carried in the lymph stream to thc left lobe of tlie livcr. Norris ('OX) a i d Koch ( '11) tlescrihed numerous lymphatics in the dog omcntum. J3y means of silver nitrate p i q a r a t i o n s , Pasparis ( '1 8 ) demonstrated omeiital lymphatics along the 1a~g-eblood ~ e s s ~ lbut s , bc failed in all attempts to inject these channels with color masses. In the same year Haurn ('18) sunimarizcvl the results of his 197 198 PARRE H. SlRfER extensive studies of the lymphatic system in the dog. Nc described orneiital lymphatics which accompany the blood vessels iii the fat strips. By injecting these cliannels with color masses lie demonstrated that the lymph vessels of the omentum drain into nodes near the duodenum and spleen, and from these collecting points the drainage is successively to tlie portal nodes, tlic iritest,iiial lymph trunk, arid the cisterni chyli. Recent iiirestigators are apparentlv uiia\var~ of H t i ~ r ~ i ' s observations. Hamazalii ( '25) noted numerous lymph chaniiels in the milk spots of the dog omentum hut did not discuss tlic coiinections between these ressels and those descrihed by previous workers. In his omental studies of rarious laboratory animals, presLirnab1:- iiicliiding the dog, Poynter ( '28) does ziot melition the presence of lymph chamiels. IIiggiiis arid Rujii ('30) studied sections of dog omenta bnt d o not record that lymph vessels were observed. This omission inclicatcs that many present day anatomists doubt the psistence of omental lympliaties in the dog. The presence of lymph chaririels in the cat omeiitum has been geiierally denied siiice the publication of Ranvier's ohscrrations (1896). He reported that such cliaiiiiels oclcur onl>- in tlic i i c ~ ~ b o rkjntten and they disappear by regression, leaving no indication of their existence i n the adult. Shipley aiid Cunniiigham ( '17) were uaable to ideiitify lymph cliaiiiiels in the sections of cat omciita x4iicli thcy studied, aud IIamazaki ('2.5) stated that the lymph vessels in tlic milk spots a r e riot clearly secii. Poyiiter ( '28) studied scctjoiis of omciita from rarious l a h o r a t o ~ yanimals hut did not report the o ( m r rerice of omeiital lymphatics in the cat. In their recent study of this animal, Higgiris and Baiii ('30) isolated the distal portion of the omentum in a subcntaiieous poucli. A few d a p later they injected a graphite suspeiisjoii into tlie poiich, after mlijch animals were Billed at snccessirc intervals and regions of graphite infiltration noted. On the basis of these observations thep state that the routes of drainage from the distal part of the omentum iiivolve the gastrolienal ligament, the OMNNTAT, LYMPHATICS 199 dorsal surface of the stomach, the lesser omentnm aiici caudate lobe of the liver, the coronary ligament of the liver, thc lymph vessels of the central tendon of the diaphragm, and the anterior mediastiiial lymph nodes. These investigators were unable to demonstrate coricliisively the presence of omerital lymplialics iii this animal. Tt appears, therefore, t h a t anat,omists in general agrce with Ranvier’s statement that omental lymph vessels do not occnr in the adult cat. iii a n artery, A ; Fig. 1 Pliotoinicrogrsph of ij section of dog o m ~ n t ~ ~showing veins, V ; the Inrgpr with valre, and numerous Iymphatjc chaniicls, 1,. Three nerves are shown to t h e left of the arterial wall. X G O . OHSERVATIONB O N TIIE DOG OMENTVM I n view of the lack of agreeincut concerning the existence of lymphatics in the omexitum of tlic dog, serial sections from cliffercnt parts of this organ were preparcd mid studied. In every preparation numerous lymph chaiiriels were easilJ- identified in the fat strips which accompany the blood vessels (fig. 1). These lymphatics consist of a n anastomosiiw nlexns of thiii uvilled vessels surrounding thc artery, aiid one or more 200 PARKE H. SIMEI: solitary channels, located in the pxivascular f a t some distance from the blood vessels. The chaiiriels comprising the arterial plexus lie adjacent t o tlie adventitia of the arterial wall and a r e often much compressed. The outlj-ing or solitary vessels a r e usually larger in size and appear almost circnlar in traiisverse section. All omental lymphatics are lined wj t h a distinct endothelium and have numerous valves. 9 more complete picture of the omental lymph vcssels in the dog was obtained by injecting them with filtered India ink. This mas accomplished by forcing the point of a sinall (27 gauge) hypodermic needle through the perivaseular fat until it was quite closc to the arterial wall and almost parallel with it. A slight amount of pressure was theii applied to the plunger of the syringe. 111 this manner the arterial lymphatic plexus was often puiicturrd and filled with the injection fluid. It was observed that the ink iiever exteiidecl in the plexus for a distance of more thaii 1 o r 2 em.; instead, it passed through conneetirig branches to tlie solitary channels (fig. 2 a). The numher and yositioii of these chariiicls a1.e variable. A single one, lying near one margin of the pcrivascular f a t is a frequent finding, but it may cross the blood vessels from one side t o the other a i d bc ac.companied by oiie or more lymph vessels of the same type (fig. 2 K ) . Thcse continiie as tortuous chaiiricls through the perirascular f a t to the proximal attachmeiits of the omeiitum. Along the course of saeh chaiinels numerous ink-fillcd spurs of tributaries may he observed (fig. 2 (”). Further extension of the iiijection fluid into these tributaries was barred by their most proximal n l v e s . It was not possible to fill a large number of lymph c h a n n ~ l s in aiiy one omentum, f o r the irik smudge resulting from Fig. 2 Photomit-rographu of purlions of dog orrrcnta in which the lpniph c.hannels are injected with India ink. X 8. A , a short plcxus of lymph vessels surrounds the artcr? and empties by communicating branches into n more oiitlyiiig channel. Note the beaded appearance of the latter, indicating the position of valx es. 13, scveral 1) rriph channels accompanying the blood vcsucls. c!, a dense lyniphatir plems ol)r4c.urcs the blood \ eswls. O u t l ~ i n gchaimcls, one with A: spur, X, also shown. 201 202 PARKF. 1%. SIMER iiumerons attempts soon clonclecl the entire organ and made further efforts impractical. Best rcsirlts were obtained on fresh material1, for in such omenta the perivascnlar fat i s relatively traiisparcnt and tlie ink-filled chaiinels can easily he identified and followed. By meaiis of repeated iiijcctions in all regions, the draiiiage paths of the lpmphntics in the dog omentum were established (fig. 3 ) . Almost all of the lymph vessels of the veiitral leaf drain into traiisrerse coiinecting cliannel s wliicli lie near the gastroepipluic blood vessels. These lymphatics empty their contents into the duodenal Iymph node. ‘l’he lymph from a relatively sniall area a t the left side of the ventral leaf drains into collecting channels which ,zccompan;r- the left gastroepiploic vein to lymyli nodes near the spleen. The spleiiic iiodcs also drain the left onethird of tlic dorsal leaf of the omeritum, while lymph from the remainder of this leaf enters the cluodenal Ipmph node clirectly or throngh efferent channels from a minute omental node xvhich lies 2 o r 3 cm. distal to tlie duodei~aInode and is frequently absent. It may be noted that these observations a r e not entirely in accord with the statements b;r- Baum (’18) that the duodeiial node drains the right half and the spleiiic nodes the left half of the ventral leaf of the omentum. The further course of the lymph stream from the duodenal and splenic nodes was also determined by injection. Effereiit chaniiels from the duodenal nodes empty into nodes located oii either side of the portal vein. lnli injected into these portal nodes drained into the iiitestiiial lymphatic trunk, and then into the cistcrni chyli. Efferent vessels froin the splenic nodes pass pither t o the portal iiodcs or directly to the iiitestinal trunk. There mas n o indication i n a117 of these experiments that the paths of omental drainage in the dog involve the lymph vessels of the diaphragm. “rhe writer wishes t o thank Iloctoi Higgins 2nd Mr. Helfrirh, of thc P h a r macology Lkpartrnent, Unirersitp of 711iuois, College of Medicine, for their cooperation in securing material for this investigation. OMFNTAL LYMI’HATICS 203 ORSERVAT CONS ON THE CAT OWEXTUM M7he21 attention was directed to serial swtions of omerita from adult cats, it was rioted that lymph cliaiincls are it conbtant finding. This observation deserves emphasis iii view of the statements by Railvier (1896) ant3 Rhjplcy and Cunning- Fig. 3 Drawing d i o n i n g the drainage paths of the lymphstirs i n t h e ventral leaf of the dog omentum. The black spnt near the duodenal flexure is t h e duodenal lymph node. The asterisk indicates the point at which t h e lymph vessels draining the left portion of this omental ltaf pass rlorsnllj, in company with the gastroepiploie vein, t o rmptg into the splcniq lympli iiodes. Four-ninths natural size. 204 FARICE H. SIMER ham ( '17) that such vessels are not present in the omenturn of the adult cat. But the existence of omental lymphatics in this aiiimal caiinot be doubted, for they may be ohsei*ved in preparations from all parts of this organ. The omental blood vessels in tlie cat are much smaller than in the dog, and as 2, conseqnericc the lymph vessels wliicli accompanj- them are neither as large n o r as thick walled as those described in the larger animal, but they have a distiiict eiidothclial lining and iiiim~ro~w d w s . Central lymph c~lianiiels arc locaatecl betm--ren the Mood vessels in the peri~asculartissue (fig. 4), but rarely form i; plexns aroirid the artery. 0ccasioiidl~-ail outlying chaunel is observed near the blood ressels (fig. 4 A ) . liik injections accomplidietl with clifEculty irr this aiiimal, sEiow that the central channels pass iii a relatively straight course I-)etween the blood vessels (fig. 5, A, €3 and ('). The ahserice of ~itimeroi~s anastomosis between these cliaiinels is a charI-ZCt eristic f ca t 11 re iii tlie cat. Commu iii catiiig braiiche s coziiiw t such central lymphatics wit11 the small solitary chniiiiclx which cai=ry12ic lympli to the collcxtiiig iiodes, h i t which arr iiot niiinerous in any specific locality and do not sliow as freqiieiit branchiiig as was obsei.rec1 in the dog, tlioug!.h they have the typical segmented form (fig. 5). Ti1 addition to the normal inflation of the proximal portions of these vessels, it j s not unusual to find tliem filled with iiik for a short distance distal to the point of injection. This indicates that even the slight hack pressure which is employed is sufficient to overcome the aclioii of tlie i i e a i ~ ~valves. st The paths of lymph drainage in the cat are similar to those in the dog, although the ~iiimberarid position of the lymph nodes often s h o ~ 7considerable variation. A siiigle iiode is located along the median sidtl of the duodennm at the level of its superior flexure, and ventral to the pancreas. hi m e of the eighteen animals examined a second node was obscrved OMEXTTAL LYMPHATICS 205 206 PARKE H. SIMER at the same level, but 011 the lateral side of the duodenum. The splenic nodes consist of oiie or more small glands located at the distal border of the liilus of the spleen, arid a single much larger gland wliicli lies near the point of union of the gastric and splenic veins. The duodenal and splenic nodes are tlic primary collecting centers of the lyrripli stream from the omentum, and their eff erent channels lead dircctly into the intestinal lymph truiik or into the nodes located near the portal vein. X left portal node was present in every animal examined, and in two cases a smaller right portal node was observed. When India ink is injected into the portal nodes, it passes rapidly into the intestinal lymph trunk and cisterni chpli and then fills the entire thoracic duct. There was no evidcricc in these experiments that the lymph from omental vessels drains into the thoracic duct by paths othcr than those just outlined. Higgins and Rain ( '30) described transference of particulate matter from the greater. omcntiim of cats by paths which follow the dorsal surface of the stomach, the lesser omenturn arid the diaphragm. It must be emphasized that that they did not observe definite lymph channels in the greater and lesser omcnta iii which the particulate matter was being transferred, and it is therefore apparent that the paths described by them a r e riot those concerned with omental lymph drainage. I n all sections examincd in this study, omental nerves were a coristant finding. The cxistence of such nerves lias been doubted by many iiirestigators, but there is no question that they occur generally for they h a w been observed recently also in the hiimaii omentuni by the writer ('34). Fig. 5 Photomicrographs of portions n f (.at oincnta in which the lymph vessels are injcctcd with India ink. X 16. A , B, anti C, ecntral lymph channrls accompany the blood ressels and draiii into outlying colleeting channels. -4n ink filled valre siiius is seeii iicar the bifurcation of thc artery iii C . D, an outlFiiig lymph rhanncl. The sharp angle near its center iiidicatea the p e s r n c e of a valve at the junction of a trihutary. O M E N T B L LYMPHATICS 207 208 PARXF. H. SIMER SEMMARY 1 . Omciital lymphatic clianiiels accompany tlie blood T-cssels in all parts of this organ in the adnlt dog arid cat. These lymphatics consist of central cliaiiiiels which lie near the blood vessels aiid communicate at intervals with more solitary channels which lie peripherally in the perivascular fat. 2. Omental lymph drainage is by way of such outlying chaiinels into the duodenal and spleiiic lymph glands. Lymph from these ziodcs passes directly or indirectly into the intestinal lymph t ruiik and cisteriii chyli. 3 . There is no evidence that t41r lymphatic cliannels of the diaphragm play any part in omental lymph drainage in tlie dog arid cat. IiITERATUKE PIT ED BAUN,11. 1918 J)as T~gmphgefasxspstcrndes Hundes. Herlin. CASPARIS, H. R. 1918 LFinphatics of the ontcnturn. Anat. Rcc., pol. 15, pp. 93-99, v. 19% Comparative studies on the milk spotq, ‘ Tachcx laiteuscs,’ of Tnrious animals. Folia Anat. Jap., Bd. 3, 8. 243-265. HEGEK,1’. 1904 La bnlapage de la c.arit@p6riton6ale par I’6piploou. Arch. internat. de plipsiiul., T. 1, pp. 26-34. HIGGIh-S, (+. M., AND c‘. (;RANT RAIN 1930 The absorption and trarisference of particulate matter 11.v t h c grcnt onientuni. Surg., Gyncc. and Dhst., tol. 50, pp. 851-860. IIOCH,J . 1911 iyber das Verhalten dcs grossen Netzes (Omeiilum inajus) b r i der pcritonealei> und intcstinalen Infektion. Med. Klin., Hd. 7 , S . 1983-1984. h e r die Bedeutung und Titigkeit des grossen Netzes bri der peritonealen lnfrktion. Ztschr. f . IIyg. 11. Infetionskrankh., Bd. 69, S. HaMAZAKI. _ _ _ I - 417-435. NORRIS,C. C. 1908 The onientmn ; its anatomy, his to log^, aiid pliysiolog~ in health ant1 diwase. TJniv. Pelin. Med. Bull., vol. 21, pp. 119-12i. POYSTEX,(‘. W . M. 1928 Concerning the great omentum. Mrd. C‘lin. N. America, vol, 13, pp. 499-503. RANVIER,L. 1896 Aberration et regression dcs l ~ m p h a t i q u e sen vole de dCveloppeuient. Cpt. rend. Aead. Se. Paris, T. 12, pp. 578-580. ROKINSON, B. 1895 Tlic peritoneum of t,he dog. Am. Prart. and S e w s , rol. 20, pp. 368-376. SIIIPLEP,P. G., AND R. 8. CENXINGHAX 1917 The histolog?. of blood and 12 m p h t i c rpssels during the pxssagc of forcigii fluids through their wal1.i. 11. Studies on absorlhion from serous cavities. Anat. Rea. vol. 11, pp. 181-190. RI~CER, PARKEH, 1934 On the itiorphology of the omrntum, with especial reference to its Ijmphatics. Am. J . Anat., rol. 54, pp. 203-228.