origin and distribution of portal blood in the sheep

Origin and Distribution of Portal Blood in the Sheep' TREVOR HEATH 2

Veterinary School, University of Melbourne, Parkville, N.2, Victoria, Australia

ABSTRACT In sheep, the gastrosplenic and mesenteric veins converge at an angle of about 140' to form the portal vein, which is joined, along its right ventral border, by the gastroduodenal vein. At the porta, right and left branches of the portal vein diverge at an angle of 65-70' to supply separate areas that join along a line between the fossa for the gall bladder, and the middle of the left branch. Right dorsal branches leave the portal vein or its right branch near the point of bifurcation.

When 1311-albumin that had been heated was injected into the right ruminal vein and entered the portal stream in the gastrosplenic vein, no significant differences existed in the levels of radioactivity between the areas supplied by the different portal branches. When the '311-albumin entered the portal stream from either the gastroduodenal or mesenteric veins, the area supplied by the right branch contained a significantly higher level of radioactivity than the remainder of the liver. When corrections were made for an unequal distribution of blood, it was found that blood from the gastrosplenic vein was distributed preferentially to the left branch, blood from the gastroduodenal vein to the right branch, and that blood from the mesenteric vein enters the right and left branches in preference to the right dorsal branches of the portal vein.

The anatomic arrangement of the tributaries of the portal vein may affect the distribution within the liver of blood derived from the various contributing organs (Sere@, '02; Himsworth, '50; Barnett and Cochrane, '56). Some workers have found that in dogs blood from the spleen, stomach and part of the colon flows to the left lobe, and that from most of the small intestine flows to the right lobe of the liver (Bartlett, Corper and Long, '14; Copher and Dick, '28; Hahn, Donald and Grier, '45). These workers studied the distribution within the liver of either emulsified olive oil, trypan blue or radioactive phosphoric acid that had been injected into one of the portal tributaries. Other workers, who injected radioactive iodine-labelled rose bengal into portal tributaries and measured its intrahepatic distribution with scintillation counters placed on the body surface, found no differences between the two sides of the liver in the distribution of the isotope (Cole, Krohmer, Bonte and Schatten, '56). In all these experiments the dogs were anaesthetised, and altera- tions in the relative positions of the portal vessels may have contributed to the variations between the results (c.f. Bradley, '63).

Variations between species in the anatomic arrangement of the portal vessels

AM. J. ANAT., 122: 95-106.

may cause variations in the intrahepatic distribution of blood derived from different tributaries (Barnett and Cochrane, '56). In ruminant animals, the venous drainage from the cranial portion of the gut is much more extensive than in nonruminants (c.f. Horowitz and Venzke, '66), and the different portal tributaries probaby vary in their relative importance. Some evidence is avail- able to suggest that the distribution within the liver of blood from these tributaries differs from that described in other species (Himsworth, '50; Garner and Singleton, '53) .

The anatomic arrangement of the tributaries and branches of the portal vein of sheep is described in this paper. A descrip- tion is also given of experiments that were designed to determine whether blood from each of these tributaries is preferentially distributed to a particular branch of the portal vein in conscious, standing sheep.

Anatomy of the portal vessels Latex casts and angiograms were used to

study the anatomy of the portal venous sys-

MATERIALS AND METHODS

1 Presented in part at meetings of the Australian Physiological Society (May, 1967) and the Victorian Division of the Australian Veterinanr Association (July, 1967).

2 Present address: School of Physiology, University of New South Wales, Kensington, New South Wales. Australia.

95

96 TREVOR HEATH

tem in merino and crossbred ewes and wethers. Each sheep was destroyed and bled out, then 100-150 ml neoprene latex (Dunlop Rubber Company, Melbourne, Australia) was injected into the mesenteric vein through a PVC cannula. The latex filled the intrahepatic branches of the portal vein and flowed in a retrograde direction along most of the portal tributaries. The abdominal organs were left in their normal positions, and the sheep were stored at 4°C for several days to allow the latex to solid- ify. The cast was then dissected out, and the traces of organic matter that remained were removed by soaking in 10% sodium hydroxide.

The livers of some sheep were removed immediately after death, and the branches of the portal vein were filled with mercury. A General Electric Patrician X-ray unit was used to take radiographs of these livers. Non-screen film was used without a grid.

Distribution of portal blood Human serum albumin labelled with 1311

(The Radiochemical Centre, Amersham, England) and previously heated was injected into one of the tributaries of the portal vein, then the circulation through the liver was occluded and measurements made of the distribution of radioactivity throughout the liver. Three series, each of five experiments were conducted: in one series the 1311-albumin was injected into the mesenteric vein, in another into the gastroduodenal vein, and in the third series of experiments the 13'I-albumin was injected into the right ruminal vein.

Before each experiment, the sheep was anaesthetised with halothane ("Fluothane," Imperial Chemical Industries, Melbourne, Australia) and an incision made parallel to and just behind the last rib on the right side. Either the mesenteric vein draining the mid-jejunum, the gastroduodenal vein near the pylorus, or the right ruminal vein was isolated. A PVC cannula (O.D. 0.96 mm) was inserted into the lumen of the vein through a small side branch, and did not appear to obstruct the flow of blood through the vein. A second piece of PVC tubing was placed loosely around the hepatic artery and portal vein, and did not touch the walls of the vein. This tube was designed as a snare, and both ends were led

out of the incision through a larger tube. The flank incision was closed, then a tube was placed in the right jugular vein and the sheep allowed to regain its feet.

The sheep was then restrained gently in the standing position and 20 pc 13'I-albumin in 1 ml of normal saline was injected through the cannula into one of the portal tributaries. This 1311-albumin, which had been heated at 55-60°C for ten minutes before injection, was washed into the vein with 2 ml normal saline. The snare around the portal vein and hepatic artery was immediately pulled tight and the flow of blood into the liver stopped 15-30 seconds after the beginning of the injection. The sheep was destroyed a few seconds later by the injection of 20 ml of 30% pentobarbitone sodium through the jugular cannula.

The liver was removed and 63 cylindri- cal segments, each 18 X 1-2 mm, were removed from predetermined areas (fig. 1). These segments were dried overnight at 50°C, then their content of radioactivity was measured in a Geiger-Muller end-win- dow counter. The level of radioactivity in each segment was expressed in counts/ min/g of dried liver.

In another series of experiments, l3lI-albumin was injected into the jugular vein in five sheep, and the flow of blood into

Fig. 1 Segments of the liver taken for radioactivity analysis after the injection of 1311-albumin into the jugular vein or tributaries of the portal vein.

PORTAL VESSELS IN SHEEP 97

the liver stopped 40-60 seconds after the beginning of the injection. The sheep were destroyed with pentobaritone sodium and measurements made of the distribution of radioactivity throughout the liver.

Student’s “t” test, coupled with an analysis of variance, was used to determine whether significant differences existed between different areas of the liver in the distribution of radioactivity. These tests are described in detail in the Observations section.

OBSERVATIONS

Anatomy of the portal vessels The portal vein in sheep is a dorso-

ventrally flattened vessel, 1.5-3 cm long, formed by the confluence of the gastrosplenic and mesenteric veins (figs. 2, 3 ) . A third tributary, the gastroduodenal vein, enters the right ventral border of the portal vein at almost a right angle, and conveys blood from the abomasum, duodenum, pancreas and omentum (figs. 2, 3) . Al- though all the venous blood from some abdoniinal organs enters the portal vein through a single tributary, either two or all three tributaries may convey blood from

some organs (fig. 2, table 1). Significant variations do exist between different sheep in the arrangement of the different veins that contribute blood to the portal vein.

The gastrosplenic vein, which is formed from the splenic and left gastric veins, flows caudally and to the right for about 1 cm before it joins the mesenteric vein (figs. 2, 3 ) . The left gastric vein, the smaller of the two tributaries of the gastrosplenic vein, also flows caudally and to the right, and conveys blood from the abomasum, omasurn, reticulum and the left face of the rumen. The splenic vein is formed by the confluence of tributaries within the spleen, and is joined by veins from the pancreas, greater omentum and right face of the rumen. The epiploic and right ruminal veins extend in a cranial direction and join the caudaI border of the splenic vein shortly before its junction with the left gastric vein (fig. 2).

The mesenteric vein, which is smaller than the gastrosplenic vein, receives blood from the pancreas, terminal duodenum, and the jejunum, ileum and large intestine (fig. 2). The terminal segment of the mesenteric vein extends cranially and slightly to the

duodenum abomasum\ I

reticulum c omasurn

1um ileum

lesser curvatureof abomasum

Fig. 2 Origin and distribution of portal vessek in the sheep. The cast from which this drawing was made was prepared by injecting neoprene latex into the mesenteric vein.

98 TREVOR HEATH

Fig. 3 Relative disposition of the tributaries and branches of the portal vein. Neoprene latex casts of the tributaries and branches of the portal vein were prepared in five sheep. The angles of convergence and divergence were measured after projection of the vessels onto a horizontal plane (upper figure) or a vertical plane (lower figure) through the long axis of the vein. P, portal vein; LB, left branch; RB, right branch; RDB, right dorsal branches; GD, gastroduodenal V; M, mesenteric V; GS, gastrosplenic V; S, splenic V; LG, left gastric V.

left and approaches the gastrosplenic vein at an angle of about 140" (fig. 3 ) .

Valves were not observed in either the portal vein or its three tributaries. A large number of valves were present in the smaller veins, but these were relatively ineffici- ent and in most cases did not impede the flow of latex along the veins.

The portal vein enters the liver at the porta, and immediately receives small veins from the gall bladder and cystic duct. It immediately divides at an angle of 65-70' into the left and right branches that supply the ventral lobe and the ventral part of the dorsal lobe of the liver (figs. 2 , 3 , 6 ) . Right dorsal branches that supply blood to the caudate lobe and the dorsal part of the dorsal lobe emerge from the dorsal surface of either the portal vein at the point of bifurcation, or the proximal part of the right branch (figs. 2, 3, 6 ) .

The right branch proceeds ventrally and gives rise to 3 or 4 major branches and a variable number of minor branches (fig. 6 ) . These vessels supply a wedge-shaped segment of liver tissue: the apex of the wedge is at the depression for the gall bladder and the base along the line of the left branch of the portal vein (fig. 6 ) . The ventral margin of this segment lies along a line between the depression for the gall bladder, and the midpoint of the left branch of the portal vein. This line does not correspond to the line of division between the dorsal and ventral lobes. Generally no vessels that can be seen in angiograms cross this line, but in one liver a relatively large branch extended into the area supplied by the left branch.

The left branch, which is considerably larger than the right branch of the portal vein, curves ventrally and to the left within a deep depression on the liver surface. A number of small branches leave the cranial surface of the left branch, and supply that portion of the liver in the region of the

TABLE 1 Tributaries through which blood from different abdominal organs enters the portal vein

Blood from + Spleen J;&:m enters portal fore- Abomasum Duodenum large Pancreas

intestine veinin .L stomachs

Mesenteric V. X X X Gastroduodenal V. X X X Gastrosplenic V. X X X


TABLE 2 Distribution of radioactivity in the liver after injection of lS*I-albumin into jugular vein, and

portat tributaries

Error Degrees

freedom

Mean cpm/g DW in area of

Left 1 Right 1 dorsal Right Remainder 2 Total mean of lalkalbumin

injected into square 3

Jugular V. 2527 2834 2868 2435 2625 211,582 248 Mesenteric V. 3473 3989 3133 3397 3505 1,086,313 248 Gastroduodenal V. 2579 4006 2917 2928 2960 3,442,497 248 Right ruminal V. 2412 2473 2236 2171 2357 595,272 248

Total no. of segments 155 60 50 50 315

]Area supplied by right dorsal branches of portal vein contains segments SE-G, 9E-G, 1OA-D, and area supplied by right branch contains segments 7A-D, 8A-D, 9A-D (fig. 1): left branch supplies all segments in strips 1-5.

2 Samples 6 A 4 , and 7 E 4 , were from intermediate regions between identXabIe drainage areas. 3 Estimated during analysis of variance.

caudal vena cava. At the level of the umbilical fissure, the left branch divides into dorsal, intermediate and ventral rami (fig. 6 ) . The ventral ramus divides into two vessels that supply the liver tissue on either side of the umbilical fissure, and the dorsal and intermediate rami, which may arise from the common trunk, supply the remainder of the ventral lobe (fig. 6 ) .

Distribution of portal blood Estimates were made of the mean levels

of radioactivity within each series in the areas supplied by the right dorsal, right and left branches of the portal vein (table 2). It was considered that the right dorsal branches supplied segments 8 E-G, 9 E-G and 10 A-D, the right branch segments 7 A-D, 8 A-D and 9 A-D and that the left branch supplied all the segments in strips 1-5 (figs. 1, 6). Student’s “t” test was used to estimate the significance of the differences between the mean levels of radioactivity in the different areas (Z -k). The “t” values were calculated by substituting the mean values, the error mean square (EMS), estimated in an analysis of variance (table 2), and the total number of segments in each area (N1, N,) in equation (i).

When the iS’I-albumin was injected into the right ruminal vein, no significant differences were apparent between the levels of radioactivity in the different areas (fig. 4). When the 1311-albumin was injected

into either the mesenteric vein or the gastroduodenal vein, the mean levels of radioactivity in the areas supplied by the left branch and the right branch did not differ significantly, but these levels were significantly less than those in the area supplied by the right branch of the portal vein (fig. 4, table 3 ) .

In these experiments, the i311-albumin would not have had time to escape from the blood vessels, and the unequal distribution of radioactivity must have been due to variations either in the amount of blood represented in each gram of dried liver, or in the concentration of 1311-albumin in this blood, or in both these parameters. An attempt was made to determine the relative importance of each of these parameters in contributing to the variations in the distribution of radioactivity observed in each series. Initially, ’”I-albumin was injected into the jugular vein in an effort to produce a uniform concentration of radioactivity in the blood entering the liver. When measurements were made of the distribution of radioactivity in the livers from the jugular series, it was found that although the areas supplied by the right and right dorsal branches contained a fairly uniform level, these areas did contain a significantly higher level of radioactivity than the area supplied by the left branch (fig. 4, table 3). These results indicated that the volume of blood represented in each gram of dried liver did vary throughout the organ.

The intrahepatic distribution of radioactivity in each of the mesenteric, gastroduodenal and right ruminal series was then

100 TREVOR H E A T H

jugular right ruminal

mesenteric gastroduodenal

Fig. 4 Distribution of radioactivity within the liver after the injection of 1311-albumin into either the jugular, mesenteric, gastroduodenal or right ruminal veins. Within each series, the shaded area, supplied with blood by the blackened branch of the portal vein, contained a significantly higher level of radioactivity than the unshaded area.


TABLE 3 Comparison of levels of radioactivity between areas supplied by different branches of the pmtal ve in

~~

Comparison within series 2 Comparison with jugular series 3 1W-albumin injected into t P t P

Jugular V RD v R 0.39 > lo-’ RD+R L 5.62 * < lo-‘

Mesenteric V L v RD 1.62 > 10-1 L v R 1.20 > 10-1 R L+RD 5.39” L + R RD 4 .30” < 10-4

GastroduodenalV RD v L 1.12 > 10-1 L v RD 0.001 > 10-1 R L+RD 4.94“ < 1 0 - 5 R RD+L 3.84 g< < 10-3

1.86 > lo-’ Right ruminal V R v RD 1.61 > 10-l R v RD L RD+R 0.49 > lo-’ L RD+R 6.86” < l o - *

lThe right dorsal branch of the portal vein is designated “RD,” the right branch “ R and the left branch

2 “t” values were calculated by substituing data from table 2 into equation ( i ) . 3 “t” values calculated by substiting data derived from table 2 into equations (i i) and (iii). * Highly significant difference.

“L”.

compared with that in the jugular series to determine whether ’3’I-albumin, injected into a portal tributary (T), was uniformly distributed throughout the blood that entered the right, right dorsal and left branches of the portal vein. In this comparison, the difference obtained in each of the mesenteric, gastroduodenal and right ruminal series between the mean level of radioactivity in the areas supplied by two of the portal branches (1, 2) was calculated (% - %). This difference was compared with the corresponding difference obtained in the jugular series (ZJi - %). The variance of the difference between these differences, equal to the sum of the respective variances ( V G + V?J2 + VFTi + VZ,,), was estimated from the error mean squares and sample numbers (table 2), and “t” was estimated from equation (ii).

A similar, independent test was used to compare these two areas with the area of distribution of the third branch of the portal vein. In this test, the “t” variable was estimated by substituting values from table 2 into equation (iii).

(iii)

The number of degrees of freedom of each error mean square used in these tests was so large (248) that the “t” variables closely approximated normal variables and it was

possible to estimate the probabilities from tables of the normal distribution (Fisher and Yates, ’63) .

These tests revealed that when the 13’I-albumin was injected into the mesenteric vein, the concentration of radioactivity in the blood did not differ significantly between the right and left branches of the portal vein (fig. 5, table 3 ) . The concentration in these branches, however, was significantly higher than that in the blood that entered the right dorsal branches. In the gastroduodenal series, the initial comparison between the right dorsal and left branches revealed a striking uniformity of concentration, but this was significantly less than that in the right branch (fig. 5, table 3 ) . When the 13’I-albumin was injected into the right ruminal vein, the concentration of radioactivity in the right and right dorsal branches did not differ significantly, but this was significantly lower than that in the left branch of the portal vein (fig. 5, table 3 ) .

Similar tests were used to determine whether significant differences either in the total level of radioactivity or in the concentration of radioactivity in the blood existed between the areas supplied by each of the three rami of the left branch (fig. 6). When the ‘”‘I-albumin was injected into the gastroduodenal vein, the area supplied by the left ventral ramus contained a significantly higher level of radioactivity than the remainder of the left lobe (P < lo-’). In this series, the blood in the left ventral

102 TREVOR HEATH

mesenteric right ruminal

gart rod uode nal

Fig. 5 Distribution within the liver of bIood derived from the mesenteric, gastroduodenal or right ruminal veins. The blood derived from each of these tributaries is preferentially distributed, through the blackened branch of the portal vein, to the shaded area of the liver.


Fig. 6 Angiogram of a sheep liver in which branches of the portal vein were filled with mercury. Left (L) and right ( R ) branches of the portal vein separate at the porta (P ) and supply separate areas that join along a line between the fossa for the gall bladder (GB) and the middle of the left branch. The left branch divides, a t the level of the umbilical fissure, into dorsal (D) , intermediate (I) and ventral ( V ) rami. Right dorsal branches (RD) emerge from either the portal vein or the right branch, and supply the caudate lobe and the dorsal area of the dorsal lobe.

104 TREVOR HEATH

ramus also contained a significantly higher concentration of radioactivity (P =

than the blood in the dorsal and intermediate rami of the left branch.

Comparisons were also made between the marginal and central areas of each lobe. In the jugular and right ruminal series, the marginal areas of both right (P < 5.10-', respectively) and left lobes (P < lo-* respectively) contained significantly higher levels of radioactivity than the respective central areas. In the right ruminal series, the blood in the marginal areas of both right (P < 5.10-') and left lobes (P < 2.10-3) also contained significantly higher concentrations of radioactivity than the central areas.

DISCUSSION

In the sheep liver, the line of division between the dorsal and ventral lobes (Sisson and Grossman, '53) does not correspond trt the line of separation between the areas supplied with blood by the right and left branches of the portal vein. It has been known for many years that a similar condition exists in the liver of man and the dog (Bartlett, Corper and Long, '14; McIndoe and Counseller, '27; Hjortsjo, '5l), and in 1953 Garner and Singleton sug- gested that this may apply in the sheep liver, but provided no clear evidence to support their suggestion. Garner and Singleton considered that the right branch is the direct continuation of the portal vein of the sheep as it is in man (Bartlett, Corper and Long, '14; Elias, '63), and that the left branch diverges at about a right angle. In the sheep examined in this study, both right and left branches diverged from the line of the portal vein, and the total angle of divergence was less than a right angle (fig. 3 ) . It is not likely, however, that the angle of divergence of the portal branches will affect the distribution within the liver of blood derived from the different portal tributaries (c.f. Barnett and Cochrane, '56).

The results obtained by Barnett and Cochrane ('56) in an in vitro system indi- cate that the disposition of the portal tributaries themselves is likely to affect the intrahepatic distribution of blood derived from the different tributaries. In ruminant animals, the exact arrangement of the por-

tal tributaries may vary depending on the degree of distension of the rumen. Al- though some variations in ruminal distension may occur under normal conditions, major variations may occur during anaesthesia (Wright and Hall, '61). This may explain the variability in the results of Garner and Singleton ('53) who injected colloidal chromic phosphate into the spleen of anaesthetised sheep and goats and studied the distribution of radioactivity within the liver.

The exact arrangement of the tributaries of the portal vein does vary considerably between different species of animals. In the human, dog and goat, the gastrosplenic vein conveys blood into the portal vein in a generally cranial direction (Bartlett, Corper and Long, '14; Miller, Christensen and Evans, '64; Horowitz and Venzke, '66), but in the sheep it extends caudally and-to the right at its termination (figs. 2, 3 ) . In the sheep, the gastrosplenic vein is the largest tributary of the portal vein, but in the dog it is only about one-half to two- thirds as large as the vein that drains the intestines (Miller, Christensen and Evans, '64).

The intrahepatic distribution of blood from the different portal tributaries in sheep varies from that described in other animals. When '3'I-albumin entered the portal stream in the gastrosplenic vein of standing, conscious sheep, there were no significant differences between the levels of radioactivity in the areas supplied by the right and left branches of the portal vein. However, when these results were corrected for variations in the total amount of blood represented in each gram of dried liver, it was found that the blood from the gastrosplenic vein had flowed preferentially into the left branch of the portal vein. The difference between the amount flowing to the left and right branches was much less than that found by Hahn, Donald and Grier ('45) in the anaesthetised dog. When these au- thors injected labelled phosphoric acid into the splenic vein, they found that the left margin of the liver contained up to 4.5 times more radioactivity per gram than the right margin. When the injection was made into a branch of the mesenteric vein, the level of radioactivity in the right section of


the liver was about three times as high as that in the left section (Hahn, Donald and Grier, ’45). In the conscious sheep, the area supplied by the right branch of the portal vein also contained a higher level of radioactivity than that supplied by the left branch when l3lI-alburnin was injected into the mesenteric vein (table 3). How- ever, this was due almost entirely to variations between the areas supplied by the right and left branches in the amount of blood represented in each gram of dried liver. There was no evidence that blood that drained from the intestines in the mesenteric vein of sheep was preferentially distributed to either the right or left branches of the portal vein. The blood from the proximal duodenum and abomasum that entered the portal vein in the gastroduodenal vein was preferentially distributed to the right branch, but some blood from the abomasum also entered the portal vein in the gastrosplenic vein, and this was preferentially distributed to the left branch of the portal vein. It may be concluded that no major variations exist between the right and left branches of the portal vein in the distribution of blood derived from the abomasum and intestines of sheep.

ACKNOWLEDGMENTS

This study was supported by USPHS grant 1 R 0 5 TW00190-01. Mr. C. K. Herbert, and Miss B. Laby and Mr. J. S. Maritz of the Department of Statistics, University of Melbourne, were of considera- ble assistance during the analysis of the results. Mr. D. J. Meehan and Mr. A. J. Forman provided valuable technical assistance.

LITERATURE CITED

Barnett, C. H., and W. Cochrane 1956 Flow of viscous liquids in branched tubes With refer- ence to the hepatic portal vein. Nature, Lond., 177: 740-742.

Bartlett, F. K., H. J. Corper and E. R. Long 1914 The independence of the lobes of the liver. Am. J. Physiol., 35: 36-50.

Bradley, S. E. 1963 The hepatic circulation. In: Handbook of Physiology. Section 2, Circula- tion Volume 11. W. F. Hamilton and Philip Dow, eds. American Physiological Society, Washington, D. C., pp. 1387-1438.

Cole, J. W., J. Krohmer, F. J. Bonte and W. Schatten 1956 A n experimental study of intrahepatic distribution of portal blood. Surg. Gynec. Obst., 102: 543-544.

Copher, G. H., and B. M. Dick 1928 “Stream line” phenomena in the portal vein and the selective distribution of portal blood in the liver. Arch. Surg., 17: 408-419.

Elias, H. 1963 Anatomy of the liver. In: The Liver Morphology Biochemistry Physiology. Volume 1. Ch. Rouiller ed. Academic Press, New York and London, pp. 41-59.

Fisher, R. A., and F. Yates 1963 Statistical tables for biological, agricultural and medical research. Oliver and Boyd, London.

Garner, R. J., and A. G. Singleton 1953 Lam- inar flow in the portal vein of the sheep and goat. J. Comp. Path., 63: 300-303.

Hahn, P. F., W. D. Donald and R. C. Grier, Jr. 1945 The physiological bilaterality of the portal circulation. Streamline flow of blood into the liver as shown by radioactive phosphorus. Am. J. Physiol., 143: 105-107.

Himsworth, H. P. 1950 The liver and its dis- eases. Second edition. Blackwell Scientific Pub- lications, Oxford, pp. 26-28.

Hjortsjii, C. -H. 1951 The topography of the intrahepatic duct systems. Acta Anat., 11: 599- 615.

Horowitz, A., and W. G. Venzke 1966 Distribu- tion of blood vessels to the postdiaphragmatic digestive tract of the goat: celiac trunk-gastroduodenal and splenic tributaries of the portal vein. Am. J. Vet. Res., 27: 1293-1315.

McIndoe, A. H., and V. S. Counseller 1927 The bilaterality of the liver. Arch. Surg., 15: 589- 612.

Miller, M. E., G. C. Christensen and H. E. Evans 1964 Anatomy of the Dog. W. B. Saunders Company, Philadelphia and London.

Seregb, H. 1902 Sur la teneur en we6 de chaque lobe du foie en rapport avec les phases de la digestion. Compt. rend. SOC. Biol., 54: 200-202.

Sisson, S., and J. D. Grossman 1953 Anatomy of the Domestic Animals. W. B. Saunders Com- pany, Philadelphia and London.

Wright, J. G., and L. W. Hall 1961 Veterinary Anaesthesia and Analgesia. BalliBre, Tindall and Cox, London.

origin and distribution of portal blood in the sheep

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