CONGENITAL LYMPHATIC OEDKMA IN AYRSHIRECALVES

by BEDE MORRIS'. T). r . BI.OOD^ W. K. STD:\iAN-'. .1. I)..\N-n .1. n .

{From KanoiiiatHLi .Memorial Institute of Patluilojiv, Sydney Hospital'; Facilityof Veterinary Science, Ihiiversity of Sydney-; Veterinary Practitioner, Uainden,

N.S.W.3).

(Accepied for inihfkation, Utk October, 1953.)

Congenital oedema in Ayrsliirc calves has ijeen recorded in Scandinaviancountries, in Scotland and in New Zealand {Hancock, 1950; Donakl. Deas andAVilson. 1!)5; ). Donald vt al. analysed data from 325 cjdves with oedema, payinj?imrticular attention to the yenetical nature ot ' the condition. The term "drop-.sical ealve-s," as used liy these autliors, does not seem adecjuate as oedema canarise in a variety of wnys, Althonsh they were aware of this difficulty andwent to considerable lengths to ensure that their materiul was homo^^eneons, theirclinical and patholojjical deserijitioii of the condition is not complete. This su^j-jicsts the need for sound diagnostic criteria before a t^enetical analysis of con-{reiiital abnormalities is nndertaken. It seems that some of the calves describedby these authors are similar to the two calves with conjicnital oedema descrilwdherein. These are believed to be tiie tir-st recorded in Australia.

CLINICAL ( )BSKBVATIONS.

llLstnn/. Tin- nilvi's were ulitjiiii.-d frtirri ii ynidi- Ayr.sliin- licnl in tlu- Cniii'Ii'ii district,Nfw Hdiitli WiiU'.s. Tlii^y wcrt' JHIIOIIK [ir<)tr,.n_v of n Imil iiiiitt'd witli IT) of liis liH]f-.sisters.B"tli cjilv.'s were oo.tciiiatou.s ,it hirtli Iiiul (lir di-liv.Ty uf one wa.- sissist.-d by the owner. Oneiiiiiiiiiii HNS 11 heitVr nnd tlu> utlicr (i bull riilf. WIi.'ii prpsi-ntrd for investigation on J6thSf|it.'nib.T. IML*, they were five weeks HiicJ tpti days oM respectively.

ri>!,..inil txamination. Both ralves were alert and bright. Their dispofition was nurmalan.i growth wiw not retarded. Their t'xer.-i«e tdleran.-e WHS not notably di'ti.-i.-iit. althiiut-'htheir movements were a little cluni.sy. Their cardinal si^ns were ..'y.si>iitialiy normal. Theirbody temperatures were H)L*.9= F. ;>nd l()-2-2" F., their lieart rates aii.I pulse rates were 10(1and N4. and llieir resj^iratuiT rates 'US and IH per minute. The pulse .•hara.'lerw were normal,th.> <-ardi:ic impulse wa.s lK.t vi^.iJ.t(' hut was readily palpable and the heart sounds wen- mprnial.The breath .sounds were normal iind there was no distensinn of the abdomen or detectableas<ites. The vi.Hible mucous membranes were slightly pallid. The chief abnormality in bothliilves WHS a striking oedeiTia of the head and limbs fFig. 1). The oedema of the heail wasmost prominent in the intermandibular .spHce, but it HISO exten.ied t<» involve the cheeks, themuzzle Hnd the eyelids. On superficial examination the ear.s did not appear oedemaloiis' hutIhey were slitrhlly thicken.'d and did pit on pressure. A small accessory lube, approximately2-5 cm. X - - 5 cm., aro.- e from the dorsal surface of Ihc left ear of (he hull ealf. There

Austral. J. exp. Biol. (195i), 32, pp. 266-274.

266 B E D E MORRIS , 1). C. BI.(K)I) ANP O T H E R S

waw il ( l i s t i iK- t .swi'lliiiff o f iill t h e l i i n l i s ;ni<l t in- ti,sMui^s p i l t c d r i ' i u l i l y o n ( i

In each linili the (*vvelliiig was difFuse and synimptrical. In tho forclimiit* it oxteiult-d fromthe coroncf to the elbuw, and in the hind limbs, ivhcTC the swfllinti was K^pateat, t'l-oni theI'oroiiet to the wtiflu jomt. There waa 3lij>;ht oedema of the tiill and the tissues overlyin(f thestemiiin. In the last two .situations the oi'di'ina was uot readily visible J>uf was easily detectedon palpation. Tlic yuunger Inill f-alf shuvveil :i greater decree of oedema tlian the oider lu'ifi'r

.-air.Diagnosis. Tlu' outstaiidiajj

feature of the clinieal syndromewas oedema which had beenpresent from birth. Fron:i thepoint of view cif diagnosis, themost intriguing feature uf thecondition was theof the oedema. As arule, most conditions causingoedema lead to a swelling ofthe tissues in dependent partsof the body. Altliough theoedema in the.«'e i-alves was mustmarked at the extremities, it in-eluded such tissues as the earsand eyelids. The unusual dis-tribution of the oedema fluid,combined with the normality oftlie cardinal signs, .suggestedthat the oedenui was not ofeardiae. hepatic, renal, infec-tious, parasitic, thyroid or nutri-tional origin. Having excludedthe more common pathologicaltypes of oedema on clinicalgrounds, a provisional diagnosisof congenital lyiiiiihatic oedemawas made. Tlie calves wero ad-mitted to h().-i[)ital for detailedinvestigation. Whilst in hospitalthey were fed rec^onstitutcflpowdered whole milk at the rate

Fig. 1. Lateral aad posterior \'iews whowiTig oe'ienuiof face and hind limbs.

of 8 oz. daily in two feeds. Thisprovided a jirotein intake ()fapproximately l>5 gm. per day.The heifer conimenced to si-ourafter H days and, in spite- of the oral administration of strejitomycin and an astringentmixture, the diarrhoea became progressively worse. The l-uli accepter! the reconstituted dietand siifFered no digestive disturbance during the 5 weeks he was ke})t under observation.

La bora fur I) iiivi'stiffdtinns. The results ol' investiiiations nn botli calves arelisted in Table 1. The low serum protein levels in both calves were intfM-pvetedas beinj; the most si{?nificant of the laboratory findinfjs. Because oT this andthe more extensive nature of the oedema in the bull c-alf, an attempt was madeto raise the scrum protein level in this aninuil by transfusion. L'itrated bovine

CON(iENITAL OEDEMA 267

jilasina with a total protein value of (i-T tiin. p.t'., alhtiniiii 4 •£]]]. |).c. and mlol)iilin2-7 ffiii. p.e. was ^iven intravenously, 350 ml. on :24tli Septembe]- iiiid 700 ml.titi 'ifitii Seiitciithei'. Tlie total ainoiint of protein j^iven was some 70 <>:ni. Thecair.s weiji'ht prior to tlie transfusion was H:.J \h. and was unelianywl in thej)eriofl followinjj the transfusion. Serum protein vahies before and aftei- t rans-fusion nve shown in Table 2.. No clinir'al {'hiinse in tiie cjilf's conditiuii tVilIowedt h e i T ' a r i s l ' n s i i i i i n t i d t h e o c i l i ' i i w i s l u i w e d n o s i f j n o f r

I

Fig. 2 . I ' o i i . n t ly i t i j i t i n m i i ' , t M ' i t i T .T . ( '[irfi>.\ r t ' l H t i v f l y ruir r i iH! . O c i it,ow power, ('ortcx.

(A) V e r y t . iw

nil o f niL 'di l l l i i .F i g . 3 . ( .^ ) t . i l t I ' l I ' l l I N ; i l ] \ i i i | i | i i H n l r . I r r i I ' l T , \ ' f i \

low power. liitT'tiiKKlut Jind cxiriinoilal l_viiipli;iiij.'i(;t.'tii-.sis nnd diiiiiriutioii of corticiil lissiu'. (B) Rit;lil ii.\it-Inrv lynipli node. huH. Vory low power. DiliitJition nfsiitii'jq'.siiliir siiiii.s and of cnrtica] iyinpli

The eleetroplior-t'lic pat tern of tlie hull eaH"s .'ici-uni was examined, t^^the scrum of a normal calf of the same affe. The j jattcrns ajipeared essen-

tially similar except thai that of the oedematous eall' showed an almost eoin]ileteahsenci' of Ihose proteins with the lowest electrojihoretic mobility. This liudinjriiidicato<l that the <;lobulin fraction was deficient and since the inittern wasd<'lei-inined when the calf was 16 days of aj;i', it is i)r(ibable tliat it had notabsorbed colostral ^'lobidin. It has since been learnt from the owner that tlie calfwas luiable to suekle inunediately after bir th , and was fed eolostrum by hand.

BEDE MUUUIS, D. ('. BLOOD AND O T I I K U . S

TABLE 1.

Heifer Hull

Hb.Ked celts S,2White cells

DifFereiitial:Neutrophiles f.-icgmcntcd)Lymphocyte.-iMoiiocytes

Bloofl gliicojieSeruiTi proteinScrum r'lituridesScriim »

10-1

7,700

10-.I gm. p.c,7.SH0.00O

iJJ) [I.e. .1(1 ]i,r,42 p.c. 54-5 p.c.

'\ p.r. S-5 p.c.109 mgm. )i.c. 145 mgui. p.c.5-4 gm. p,c, 4-7 jj '"- P-*-405 mgm. p.c, 405 mgm. y.r.•U\2 mgm. p.c. 410 mgiii. ji.c,1-5 gm. p.c. 1-24 gm. p.c.423 mgm. p.c. 42S lugm, p.c."

12-5 mgm. p.c. 12'5 nigni. p .c*

* Pooled aliquots from each calf.Urine samples from both calves were negative for sugar, [iroteiii, blond, (-asts aixl

'liat ci'lls.

Oedema fluid jirotciiiOedema fluid sodiumOi'deinif fluid potassium

r i g . 4. i;i^;li[ p i rn i i ra l tyiiipli nude, bull. {Al Verylow power. Showing isolated tymphoid follicles. (B)Low power. Showing dilated lymphatic vessels sur-rounding foltii-tcs.

•I .• y

F i g . 5 . L y u i p l i v e s s e l f r o m r i ^ j l i i a x i l l a , l u i l l , ( AL o w j i o w e r . I n l i i i i a l j i r o l i t ' e r i i l i o n i i t i d s t r a n d t ' ( i n i i : ition. (H) High power view Khowing detailed structunof strands.

CONGENITAL OEDEMA 269

TABLE 2.

Total protein Albumin Globulingm. p.c. gm. p.c. gm. p.c.

Before transfusion 4-9 3*6 1-4Tmmediately after 5-1 3-6 1-524 hours after 4-9 3-4 1-5

Further investigation of the heifer was deemed unprofitable due to thedevelopment of severe dysentery, and she was autopsied eight days after ad-mission. The post-mortem findings in tliis animal pointed to an anatomical andmechanical derangement of lymphatic function, and it was considered thatfurtlier attempts at treatment of the bull would be futile. Twenty-four hoursbefore autopsy an attempt was made to assess the function of the fore and hindlimb lymphatics of the bull calf. Twenty ml. of dye-albumin solution (10 mg.T1824 per ml. of a 10 p.c. solution of crystalline bovine albumin) was injectedsubcutaneously into one fore and one hind limb near the fetlock. Absorption ofthe large molecular dye-protein complex occurs only by way of the lymphaticsystem (Courtice and Siiumonds, 1949). Serum samples taken over the following12 hours failed to reveal any detectable dye in the circulating blood. This sug-gested that there was little movement of lymph from the oedematous skin eventhough the calf was exercised.

PATHOLOGICAL OBSERVATIONS.

Post-mortem examination.

Each calf in turn was destroyed by intravenous barbiturate administration.The general distribution of the oedema confirmed the clinical findings. Theoedematous areas were gelatinous in appearance, containing much straw-colouredfluid which dripped from the cut surface. In the bull calf the dye-protein complexhad not moved i'roin the injection site in the hind limb, while in the fore limb avery small proportion had reached the prescapular lymph node via an afferentlymphatic vessel, and a trace had penetrated to one of the cranial mediastinalnodes. However, nearly all the dye had remained at the injection site in thedistal region of the fore limb.

The superficial lymph nodes were variable in size and appearance; mostwere smaller than normal with numerous cystic dilations, more particularly inthe medullary zones. The right precrural node of the bull calf reseml)led amulberry. The afferent and efferent lymphatic vessels could be seen on carefuldissection to be enlarged, tortuous and dilated. In the limbs the intermnscularfascial planes were much more prominent tliau normal, and the same appearancecharacterized the intramuscular connective tissue, so that the muscles appeared

270 BEDE MORRIS, D. C. BLOOD AND OTHERS

pale and excessively fibrous. Iu the peritoneal cavity the subserous connectivetissue was denser and more opaque than normal, the serosa appearing deadwhite. There were 50 ml. of straw-coloured fiuid in the peritoneal cavity of theheifer calf, and 100 ml. of similar fluid in the peritoneal cavity of the bull calf.In the latter case a clot formed on allowing this fiuid to stand. The liver ineach calf was slightly small, the borders being rounded and the liver tissuefriable. In the heifer calf there was a well-marked diffuse white stippling sug-gestive of a biliary cirrhosis. The intrahepatic bile ducts were prominent, theirwalls enlarged, the structures appearing as ill-defined cream-coloured streaksand spots throughout the liver substance. In this animal, too, the gall bladderwas enlarged, measuring 10 X 8 X 7 cm.; the contents were normal and theduct patent. In both calves the adrenal cortices were narrow, being reduced toa rind of about 1 mm. iu thickness. The adrenal cortex contained a black pig-ment on the left side in the heifer calf, and, to a milder degree, on both sidesin the bull calf. The lymph nodes of the peritoneal cavity were normal in sizefor the most part, a few were slightly juicy on section. In each calf there wasa mild degree of congestion of the small intestine, and in the heifer the gutcontents were bloodstained.

In the thoracic cavity the pleura showed the same dead white appearanceas did the peritoneum. In the heifer calf there were 100 ml. of clear amber peri-cardial fiuid, and in the bull calf 15 ml. of a similar fluid. Simple dissectionrevealed that the thoracic duct of the heifer was present and dilated. In thebull calf a more complete dissection, performed with the aid of the injection ofdye into the duct at post-mortem, revealed that although the duct eventuallyopened into the venous system at the jugular confluence, it was extremely tor-tuous throughout its course, aud excessive pressure was necessary to propel dyedfluid along the duct. The only grossly abnormal thoracic lymph nodes were thesternal nodes of the bull calf, which were enlarged and soft in consistency.

Around the head, and more especially in the region of the intermandibnlarspace, the skin and subcutaneous tissues were oedematous, being some 3 cm. inthickness. There was no differentiation between the skin and subcutaneoustissue in these regions, which had a dense white oedematous appearance andfrom the cut surface of which clear fiuid dripped away. The lymph nodes inthis region were small and difficult to find. In the bull calf the thyroids weighed15 gm.

Histopathological findings.

The lymph nodes of both animals showed, in varying degrees of severity,a series of striking morphological changes. Those more centrally situated, sucJias the bronchial, mesenteric, internal iliac, hepatic, lumbar aud deep cervicalnodes, were least severely affected (Fig. 2). Some of these showed merely

CONGENITAL OEDEMA 271

diminution in lymphopoietic activity with some distension of cortex and medullawith oedema fluid, and an increase in the number of efferent lymphatics situatedin the hilar region. The walls of these efferent vessels were thin, and the vesselsthemselves were dilated. In one of these, however, there was a greater degreeof lymphangiectasis of the medullary vessels, and a fibrous thickening of theirwalls, the whole leading to a considerable loss of medullary lymphoid cellulartissue.

The peripheral nodes were more severely affected. The subcapsiilar sinu-soids and afferent lymphatics were dilated (Fig. 3). In the most severely affectednodes there was, in addition, distension of the intranodal sinusoids, with theproduction of large, apparently multiloculated, cavities in the cortical tissue,which was reduced to a series of strands of pulp surrounding these cavities (Fig.4). The right precrural node of the bull calf consisted merely of a number ofisolated lymphoid follicles which were undifferentiated except for the presenceof a subcapsuiar sinus (Fig. 4a). These were quite discrete, and set in a massof loose connective tissue containing large numbers of lymphangiectatic vessels(Fig. 4b). Scattered petechiae were present iu the lymphoid tissue. A propor-tion of the dilated vessels, both in and surrounding the affected nodes, showedstriking degrees of intimal proliferation with a tendency toward the formationof strands of eudotheliuni stretching across the lumen of the vessel, leadingoccasionally to multiple subdivision of the lumen (Fig. 5).

The liver of the heifer ealf showed marked proliferation of bile ducts. Inthe portal tracts were uumorous focal aggregations of cells which proved to beareas of active cxtramedullary haemopoiesis. These changes were not found inthe liver of the bull. In the lung of the heifer there was a distension of theiuterlobular septa and lymphangiectasis. In the adrenals there was a varyingdegree of nielanotic infiltration into the cortex aud the capsule. Tlic cortexwas reduced in thickness aud there was little lipoid present. The zona glomeru-losa a])peared hyperplastic, and in the medulla the more centrally situated cellsshowed a loss of cytoplasmic stain. Subcutaneous and subserous connectivetissue showed an increase iu collagen and an oedema characterized by disten-sion of the tissue spaces. There was very little extracellular protein coagulumpresent in the oedematous areas. The presence of an acute enteritis was con-firmed, while sections of the thyroid, central nervous system, splceu, kidney,voltmtary muscle and thymus were normal.

DISCUSSION.

The pathological findings confirmed the clinical diagnosis. There was evi-dence of a developmental abnormality of the lymphatic system, affectiug in par-ticular the peripheral lymph nodes and their associated vessels. The importantfeatures were au atrophic condition of the lymphoid follicles, associated with

272 BEDE MORRIS, D. C. BLOOD AND OTHERS

striking duplication of lymph vessels, some of which had hyperplastic wallswhilst others were thin-walled and widely dilated. In most cases there wasextensive proliferation of the endothelium of these vessels leading to the forma-tion of strands of tissue stretching across the lumen of the vessel, and in manycases dividing it completely. Whilst these structures bore an obvious relationshipto the valves present iu normal lymphatics, their morphology was more complexand very probably provided a considerable resistance to lymph flow. In addition,the thoracic duct of the bull calf, at least, was extremely tortuous and presentedan obvious resistance to the passage of fluid. These morphological abnormalities,presumably occurring during the development of the lymphatic system, wouldresult in a decreased centripetal lymph flow with the accumulation of tissue fluidat the periphery of the lymphatic chains. As the more peripheral nodes andvessels were the most severely affected, the oedema appeared characteristicallyin the regions drained by these nodes.

The development of the mammalian lymphatic system has been studiedextensively by many workers (von Recklinghausen, 18G2; His, 1863, Huntingtonand McClure, 1908; Clark and Clark, 1918 1932; Clark, 1912; and Sabin, 1908,1911, 1916). In the cat and pig in particular, the periods at which the dif-ferentiation of the various components of the lymphatic system oceur are wellestablished.

The appai-ent disturbance in endothelial proliferation which both thesecalves showed throughout their peripheral lymphatic system is significant. His(18G3), in a study of the origin of blood vessels, found they arose by differentia-tion of vaso-formative eells or angioblasts. These angioblastie eells differentiateout of the embryonic meseuchyme and form the endothelium, wliich is thecharacteristic tissue of the vascular system. The period during whieh the endo-thelial spindle cells differentiate from embryonic mesenchiane is considered tobe limited, and Stockard (1915) showed this stage of differentiation to occurin the living chick by the end of the second day of incubation when the circu-lation is establislied. This limited period of endothclial differentiation is fol-lowed by the much more protracted period of growth. The lymphatic system,of whieh endothelium is the eharacteristie tissue, begins to form well after theperiod of differentiation of endothelium from mesenchyme has ceased. Conse-quently, congenital abnormalities in lymphatic endothelial development areassociated with disturbances of tissue growth and not differentiation.

Following the formation of the early foetal arterial aud venous systems, theprimary lymphatic anlagen form near the veins from whose endothelium theyoriginate. The primary lymph sacs bud off from the anterior cardinal veins andthe veins of the Wolffian body in tlie form of two sets of paired jugular andiliac sacs, and two unpaired sacs, the retro-peritoneal and the cisterna chyli(Sabin, 1916). From these primary anlagen, the endothelium grows out by

CONGENITAL OEDEMA 273

sprouts to form eventually the peripheral hTiiphatic system. The centrallyniplmtic system thus forms first and the snbsc(!uent outgrowth of lymphaticendothelium eventually completes the peripheral system. It is from theselymphatic anlagen that the primary lymph nodes develop. These, in the pigat lea.st, include the caudal superficial cervical and deep cervical nodes (primarynode.s originating from the jugular sacs), and the deep inguinal, internal iliac,<ind lumbar nodes from the iliac sacs. Significantly these primary nodes in thetwo ealves with congenital oedema showed the least pathological changes.

The secondary and tertiary nodes, whieh form at a later date along withthe periplieral lymphatic system, wore the ones which showed the mo.st markedchanges. The secondary nodes arising from the jugular sac endothelium arethe nodes of the face and head. These showed marked abnormalities in theirlymphoid tissue component, and particularly in the endothelial elements bothwithin and around the nodes. The lymphatic vessels, which are developedsecondarily from the jugular lymph sacs and cervical plexus, supply the ears,forehead, face, lower jaw and tongue, the superficial regions of the skin of theneck, the foreleg and the superficial lymphatics of the thorax and lungs. Thesewere areas of characteristic oedema in the two calves.

The secondary and tertiary nodes arising from the iliac sacs are thosesuperficially placed in tlie hind limb region, the external iliacs, superficial in-guinal, precrural and popliteal nodes. These nodes and the superficial lymphaticsassociated with them were grossly abnormal, and the Iiind limbs, flank and taildrained by these lymphatics showed extensive oedema. In the regions drainedby the primary nodes, the peritoneal and pleural cavities and gut, only smallamounts of oedema fluid had accumulated.

The protein content of the oedema fluid was high, and this would beanticipated from the elcphantiac nature of the condition. The fact that thelymphatic system did not absorb any of the injected dye-albumin complex fromthe extremities indicates that the lymphatic lesions were sufficient to preventthe flow of lymph even though muscular movement (the force responsible forlymph flow in the norma! animal) continued for 24 hours after injection.

It appears from this evidence that the essential nature of the congenitaldefect is one involving the lymphatic endothelium, at a period following the dif-ferentiation of angioblastic tissue from embryonic mesenchyme and the formationof the primary lymph sacs and nodes. Tlie pathological changes of the peri-pheral lymphatic vessels, secondary and tertiary lymph nodes, indicate a dis-turbance in the organization and growth of lymphatic endothelium at the periodduring which the peripheral lymphatic system was developing. Secondaryeffects of pressure within and around tlie perii)heral nodes and lymjihatics nodoubt contributed to the pathological changes noted.

274 BEDE MORRIS, D. C. BLOOD AND OTHERS

SUMMARY.

The clinical, biochemical and pathological findings in two cases of congenitallymphatic oedema in Ayrshire calves have been described.

Clinically, the outstanding feature was oedema of the head and limbs. Bio-chemically, there was hypoproteinaemia and a high protein content of the oedemafluid. Pathologically, there was a developmental abnormality of the lymphaticsystem which was more severe in the peripheral lymph nodes and their associatedvessels.

The pathological findings suggest that the congenital defect was associatedwith disturbances of tissue growth and not differentiation. Since the mainpathological changes were found in the peripheral lymphatic vessels and thesecondary and tertiary lymph nodes, it would appear that the developmentalabnormality commenced at a period following the formation of the primarylymph nodes.

Acknowledgments. Grateful acknowledgment is made to Dr. F. C. Courtiee, Dr. H. S. H.Wardlaw and Professor H. R. Came for advice and assistance. Thanks are also due to Mr.L. H. Whitlock for the histopatbological preparations, and to Mr. R. J. Money, of SydneyHospital, who prepared the photographs.

BEFEEENCES.

Clark, A. H. (1912): Amer. J. Anat., 14, p. 47.Clark, E. B. (1911): Anat. Rec, 5, p. 395.Clark, E. B. (1909): Ihid., 3, p. 183.Clark, E. R. and Clark, E. L. (1918): Ihid., 15, p. 231.Clark, E. R. and Clark, E. L. (1932): Amer. J. Anat., 51, p. 49.Courtiee, F. C. and Simmonds, W. J. (1949): J. Physiol., 109, p. 117.Donald, H. P., Deaa, D. W. and Wilson, A. L. (1952): Brit. vet. J., 108, p. 227.Hancock, J. (1950): Proc. 10th Ann. Conf. N.Z. Soc. Animal Prod., p. 91.His, W. (1863): Zeitsehr. f. wissensch Zoologie, 12, cited by Sabin, F. B., Johns Hopk. Hoap.

Bept., 1916, 17, p. 347.Huntington, G. S. and McClure, C. F. W. (1908): Anat. Boe., 2, p. 1.Huntington, G. S. (1908): Ibid., 2, p. 19.von Becklinghauaen, F. D. (1862): Die Lymphgefasse und ihre Beziehung zum Bindegewehe,

Berlin, A. Hirschweld.Sabin, F. R. (1908): Anat. Bee, 2, p. 46.Sabin, F. E. (1911): lUd., 5, p. 417.Sabin, F. B. (1916): Johns Hopk. Hosp. Rept., 17, p. 347.Sabin, F. R. (1916): Science, 54, p. 145.Stockard, C. B. (1915): Amer. J. Anat., 18, p. 525.