J. Anat. (1987), 153, pp. 123-137 123 With 8 figures Printed in Great Britain The renal vascular system of the monkey: a gross anatomical description MARK J. HORACEK, ALVIN M. EARLE AND JOSEPH P. GILMORE Departments ofAnatomy and Physiology and Biophysics, University of Nebraska College of Medicine, Omaha, Nebraska 68105, U.S.A. (Accepted 12 September 1986)

INTRODUCTION Monkeys are frequently used as a model for physiological experiments involving the . It is known that physiological disparity between mammalian species can often be elucidated by a study of the structural differences between these species. Despite this fact, the monkey's renal vasculature has not been described in sufficient detail. Such a description would be useful since monkey experimentation plays an important role in understanding human physiology. Also, the branching pattern and segmen- tation of the monkey's renal vasculature is interesting from both comparative and experimental viewpoints. Fourman & Moffat (1971) indicated that although all mammalian kidneys are somewhat similar, there are several species-specific differences in terms oforganisation, microstructure and function. They conducted several extensive vascular studies on mammals, including several rodents and carnivores, but did not include any specific information concerning the monkey. Graves (1971) and Fine & Keen (1966) have described the branching patterns and segmentation of human kidneys. However, comparable information pertaining to the monkey kidney is not available. The purpose of the present study is to provide a detailed morphological description of the gross renal vasculature in the kidneys of two species of monkeys, Macacafascicularis and Macaca mulatta.

MATERIALS AND METHODS Twelve monkeys (Macacafascicularis and Macaca mulatta) were used in this study after they had been utilised for electrophysiological experimentation. Before death by pentobarbital sodium overdose, all monkeys were heparinised with 2 ml of sodium heparin (10000 units/ml) and their vascular systems were dilated by injection with papavarine hydrochloride. Perfusion techniques Following death, the thoracic aorta was mobilised and a polyethylene cannula was inserted and tied in position. The inferior vena cava was incised just above the diaphragm to allow the blood to escape during perfusion. Following this, 1000 ml of isotonic saline containing 10 units/ml of sodium heparin were perfused through the aortic cannula. Each monkey was then perfused with either neoprene latex 842A (Nebraska Scientific, Omaha, NE) or Batson's no. 17 anatomical corrosion compound (Polysciences, Inc., Warrington, PA). In some cases both compounds were used, one being perfused into the arterial and the other into the venous system. 5-2 124 M. J. HORACEK, A. M. EARLE AND J. P. GILMORE Perfusion of the arterial system with Batson's compound The arterial system of five monkeys was perfused with Batson's no. 17 anatomical corrosion compound coloured with Batson's red or blue pigment. After completing the heparinised saline perfusion, a cannula, connected to a 25 ml syringe, was inserted into the thoracic aorta and secured with a ligature. Following a five minute interval, 20 ml of compound was injected into the aorta using moderate, constant pressure, never forcing the injection when resistance was noted. (A five minute delay was allowed to increase the viscosity of the perfusion compound and thereby avoid perfusion of the smaller vessels.) Following perfusion, pressure in the system was maintained while the thoracic aorta was ligated just distal to the cannula. The injected compound was allowed to harden in a refrigerator overnight. Gross anatomical observations of the renal and its associated structures were made prior to subsequent dissection to isolate the trunk region. After the dissection, the remaining tissue, which included the diaphragm, pelvis and intervening tissue with its blood supply, was placed in a container and cleared in a solution of 5 % sodium hydroxide. The resulting vascular cast was stored in 5 % formalin. Perfusion of the arterial system with neoprene latex 842A Following the initial saline perfusion, the arterial system of three monkeys was perfused with neoprene latex 842A. The arterial system of each monkey was studied in situ, and then corroded and stored in 5 % sodium hydroxide solution using methods similar to those described above. Perfusion of the venous system In addition to the eight monkeys utilised for arterial perfusions, the venous system of two monkeys was perfused through the inferior vena cava. Following the initial saline perfusion, a cannula connected to a 25 ml syringe was inserted into the inferior vena cava just above the diaphragm and secured with a ligature below the diaphragm just superior to the renal veins. One monkey was perfused with neoprene latex 842A and the other with Batson's no. 17 anatomical corrosion compound. After refrigeration to allow time for cast hardening the kidneys and adjacent tissues were placed in a 5 % sodium hydroxide solution for corrosion. After corrosion, the Batson's cast was stored in 10 % formalin while the latex cast was stored in a 5 % sodium hydroxide solution. Combined arterial and venous perfusions Following the initial saline perfusion, in two monkeys Batson's compound was perfused into the arterial system prior to the perfusion of neoprene latex 842A into the venous system. These perfusions and subsequent corrosion and storage in 5 % formalin were accomplished using methods similar to those described above.

RESULTS The The course of the renal artery in the monkey (Macaca fascicularis and Macaca mulatta) and its relationship to other structures is similar to that observed in man. The renal arise from the lateral aspect of the aorta below the superior mesenteric artery at approximately the same level, although either may arise more cranially than its counterpart on the contralateral side. Similarly, the kidneys sometimes lie at Renal vascular system ofmacaque monkey 125 approximately the same level, or one or the other may lie cranial to its partner. A kidney lying above its contralateral partner is sometimes, in fact, supplied by a renal artery with an origin below its contralateral partner. Consequently, the path of each renal artery is variable, taking a horizontal, superolateral, or inferolateral course (Fig. 1). At, or slightly before reaching the hilum of the kidney, the renal artery divides into an anterior and a posterior division. Each division branches into segmental arteries, the most proximal portions of which can often be seen at the hilum and traced into the sinus of the kidney. At the hilum, the lies anterior to the renal artery and/or its divisions, and the is posterior and inferior to both the renal vein and artery. However, because the posterior division of the renal artery eventually passes posterior to the renal pelvis, the proximal portions of the posterior segmental arteries regularly lie posterior to the pelvis. Each renal artery may give rise to one or more inferior suprarenal arteries along its course. More distally, and frequently near the hilum, small vessels are -given off to the and to the proximal portion of the . Occasionally, capsular vessels arise from the anterior and posterior divisions of the renal artery. Capsular vessels also often arise from one or more of the inferior suprarenal arteries. In a few cases the inferior phrenic artery was a branch ofthe proximal portion ofthe renal artery (Fig. 1). Arterial segmentation of the kidney Each division of the renal artery branches into arteries each of which supplies a distinct area or segment of renal parenchyma. The size of these arterial segments, and each segment's particular vascular supply, was somewhat variable from one kidney to another, even when comparing kidneys from the same monkey. Despite the variability encountered, all sixteen kidneys could be categorised into the general segmentation scheme described below. The anterior division of the renal artery supplies approximately the anterior half of the kidney, while the posterior division supplies the posterior half, although either division may supply slightly more or less than half of the kidney. When the perfusion of casting compound is such that the glomeruli do not fill, it is possible to observe this anterior and posterior arterial division along the convex border of the kidney. In man, this division has been called Br6del's line and in the monkey is always variable in its longitudinal course so that no straight line can define, with any specificity, the parenchymal regions supplied by the anterior or posterior divisions of the renal artery. When the perfusion of casting compound results in the filling of glomeruli and efferent arterioles, this division or line between anterior and posterior arterial regions of the kidney is not discernible. This is because glomeruli of adjacent segments lie in close proximity to one another (although there are no apparent anastomoses between them) and this tight juxtaposition obscures the longitudinal line of demarcation described above. Anterior segments The anterior region of the kidney may be divided into three or four segments of variable size, each segment generally receiving its blood supply from one segmental artery. Occasionally more than one artery may supply a renal segment. This may occur when the normal segmental artery is replaced by two smaller arteries having a similar origin, or when an adjacent segmental artery distributes what might be interpreted as an anomalous branch to a segment other than its own. From superior to inferior, the four anterior segments of the kidney are the apical, 126 M. J. HORACEK, A. M. EARLE AND J. P. GILMORE

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.C Renal vascular system ofmacaque monkey 127 upper, middle and lower segments. Figures 2 and 3 are schematic representations of the approximate area of supply of each anterior segmental artery. Notice that occasionally the apical segment is replaced by an enlarged area of supply by the upper segment. Because of the variability in the size of segments, the apical and lower segments may occupy more or less than half of the superior or inferior poles of the kidney. For example, the apical (or upper) segment may actually contain renal parenchyma located posterior to the geometric midline of the kidney. Posterior segments The posterior region of the kidney may be divided into three or four segments of variable size, each segment generally receiving its blood supply from one segmental artery. Like the anterior segments, a posterior segment may be supplied by more than one artery. Variations in the origin of posterior segmental arteries also occur. From superior to inferior, the three posterior segments ofthe kidney are the superior, intermediate and inferior segments (Fig. 5). Occasionally a posterior-apical segmental artery may arise from the posterior division of the renal artery, resulting in four posterior segments (Fig. 4). The superior and inferior segments may occupy more or less than half of the superior or inferior poles of the kidney. Segmental arteries The arteries supplying the anterior and posterior segments of the kidney are named to correspond with the segments that they supply. (1) The apical segmental artery The apical segmental artery may arise from the anterior division of the renal artery, from the proximal portion of the upper segmental artery, or it may be represented by branches from either one, or both. Ifmore than one branch supplies the apical segment, the smaller branch is designated as an accessory apical segmental artery. In cases where the apical segment is supplied exclusively by several smaller branches from the upper segmental artery, with no dominant vessel present, the concept of an apical segment becomes ambiguous, and the term is not used. When present, this artery competes with the superior or posterior-apical segmental artery of the posterior division for dominance of the superior pole of the kidney. (2) The upper segmental artery The upper segmental artery arises from the anterior division of the renal artery and travels superolaterally. It may give rise to an accessory apical segmental artery. Occasionally, the middle segmental artery is a branch of the upper segmental artery. (3) The middle segmental artery The middle segmental artery arises from the anterior divison of the renal artery below the upper segmental artery. This artery may be a branch from the proximal portion of the upper or the lower segmental artery. Occasionally, a single middle segmental artery is not apparent. In this case, the parenchyma of the middle segment

Fig. 1. Anterior view of a pair of kidneys and renal arteries. Notice that (1) the right renal artery has a higher origin from the aorta than the left, (2) the renal arteries have a variable course, the right passing directly laterally and the left passing inferolaterally, (3) the left kidney is more inferior than the right kidney, (4) the inferior adrenal arteries (A) arise from the distal portion of the renal artery and (5) the inferior phrenic artery (B) on the right is a branch of the proximal portion of the right renal artery, whereas on the left it is a branch of the aorta just superior to the left renal artery. x 2. 128 M. J. HORACEK, A. M. EARLE AND J. P. GILMORE Figure 2. Figure 4.

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Anterior segmentation - Posterior segmentation - three segments three segments Fig. 2. Approximate area occupied by the apical (A), upper (U), middle (M) and lower (L) segments. Fig. 3. Approximate area occupied by the upper (U), middle (M) and lower (L) segments when the apical segment is not present. Fig. 4. Approximate area occupied by the posterior-apical (P-A), superior (S), intermediate (I) and inferior (Inf) segments. Fig. 5. Approximate area occupied by the superior (S), intermediate (I) and inferior (Inf) segments when the posterior-apical segment is not present. is supplied by a relatively large branch from both upper and lower segmental arteries. Thus the middle segmental artery has an extremely variable origin and may follow a direct lateral or slightly superolateral or inferolateral course. (4) The lower segmental artery The lower segmental artery arises from the anterior division of the renal artery, below the middle segmental artery. In one case, it was a branch of the distal portion of the renal artery arising just prior to its bifurcation into anterior and posterior divisions. This artery travels inferolaterally and may divide into two branches - a superior one, which takes a lateral course, and an inferior one, which takes a more caudal and slightly posterior course. The lower segmental artery competes with the Renal vascular system ofmacaque monkey 129 (b)

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Fig. 6(a-d. Examples ofthe magistral (a), cruciate (b), bifurcating (c) and quadripartite (d) branching patterns of the anterior and posterior divisions of the renal artery. x 1.5. 130 M. J. HORACEK, A. M. EARLE AND J. P. GILMORE inferior segmental artery of the posterior division for dominance of the lower pole of the kidney. (5) The posterior-apical segmental artery The posterior-apical segmental artery was observed in only two cases. When present, this artery is the highest branch of the posterior division of the renal artery. It supplies a portion of the superior polar region of the kidney and competes with the apical (or upper if the apical does not exist) segmental artery from the anterior division for dominance of the superior polar region of the kidney. When not present, this region of the kidney is supplied from branches of the superior segmental artery, in which case the posterior-apical segment does not exist. (6) The superior segmental artery The superior segmental artery is a branch from the posterior division of the renal artery. This artery travels superolaterally, generally supplying the parenchyma above the intermediate segment, and competing with either the anteriorly located apical or upper segmental artery for dominance of the superior pole of the kidney. When the posterior-apical segmental artery is present, the superior segmental artery supplies the region between posterior-apical and intermediate segments. (7) The intermediate segmental artery The intermediate segmental artery is a branch from the posterior division ofthe renal artery. It takes a roughly horizontal course, although it may angle slightly superiorly or inferiorly, between the superior and inferior segmental arteries. This artery may arise from the base of the superior or inferior segmental artery, and occasionally it may be replaced by a relatively large branch from both the superior and inferior segmental arteries. (8) The inferior segmental artery The inferior segmental artery is the lowest branch of the posterior division of the renal artery. It takes an inferolateral course and frequently divides into two branches. Occasionally, instead of a division into two arteries, the inferior segment is supplied by a large branch (inferior segmental artery) and a much smaller accessory inferior segmental artery, which is a separate branch from the posterior division of the renal artery. The inferior segmental artery competes with the lower segmental artery of the anterior division for dominance of the caudal pole of the kidney. Branching patterns of the anterior andposterior divisions of the renal artery The branching pattern of the anterior and posterior divisions of the renal artery is variable, but can generally be grouped for the purposes of description into one of four major patterns. These are classified Type I (magistral), Type II (cruciate), Type III (bifurcating), or Type IV (quadripartite). Examples of each type are shown in Figure 6. Type I (magistrat) In this pattern, the anterior or posterior division (or its continuation) curves inferolaterally toward the caudal pole of the kidney. As the anterior division does so, it gives rise successively to the upper and middle segmental arteries, and ends as one or two arteries representing the lower segmental artery. The posterior division successively gives rise to the superior and intermediate segmental arteries and then terminates as the inferior segmental artery. Renal vascular system ofmacaque monkey 131 Type II (cruciate) In this case, the anterior and posterior divisions each separate into three branches which originate and diverge from the same approximate point on the vessel. The three branches are named successively upper, middle and lower segmental arteries for the anterior division and superior, intermediate and inferior segmental arteries for the posterior division. Type III (bifurcating) In this case, the anterior or posterior division splits into two equal sized branches, one coursing superolaterally and the other inferolaterally. For the anterior division the superolateral branch is, or becomes, the upper segmental artery and the inferolateral branch is, or becomes, the lower segmental artery. The middle segmental artery may be a branch of either of the major branches or a branch from both. For the posterior division the branch travelling superolaterally is the superior segmental artery, and the branch travelling inferolaterally is the inferior segmental artery. The intermediate segmental artery arises from either major branch, or it may be represented by a branch from both. Type IV (quadripartite) In this case, there are four major arteries supplying the parenchyma of the anterior or posterior regions of the kidney. These arteries, the apical, upper, middle and lower segmental arteries (anterior division) and the posterior-apical, superior, intermediate and inferior segmental arteries (posterior division), are usually separate branches from their respective divisions ofthe renal artery. However, in terms ofthe anterior division, the apical segmental artery may arise from the most proximal portion of the upper segmental artery, and the middle segmental artery may arise from the most proximal portion of the upper or lower segmental arteries. In terms of the posterior division, the intermediate artery may be a branch from the proximal portion of either the superior or inferior segmental arteries. Intrarenal arterial branching After passing anterior or posterior to the renal pelvis, the segmnental arteries run parallel to the surface ofthe kidney between the renal parenchyma and the renal pelvis. The segmental arteries often branch along this course. These major branches diverge from their parent segmental arteries at any angle necessary to reach their region of supply. Eventually, the segmental arteries, or the major branches thereof, penetrate the renal parenchyma near the corticomedullary junction and divide into or become arcuate arteries. Many arcuate arteries leave their parent arteries approximately at right angles, the parent being the segmental artery itself or a major branch thereof. The arcuate arteries generally lie at the junction between the cortex and the medulla. The term arcuate is often misleading, because the majority ofthese arteries do not form perfect arches since many of them do not lie at the corticomedullary junction throughout their entire course, but rather take an oblique path through the cortex. The arcuate arteries do not anastomose with one another within one segment or between segments. An arcuate artery often terminates by turning up into the cortex as an interlobular artery, or it may end by branching into in a pattern resembling dichotomous branching. Some interlobular arteries arise as branches from the cortical side of arcuate arteries as they pass along the corticomedullary junction. Most of the interlobular arteries that arise from arcuate arteries divide into secondary interlobula'r 132 M. J. HORACEK, A. M. EARLE AND J. P. GILMORE (a) Renal vascular system ofmacaque monkey 133

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. Observe two collecting veins (CV), one above and the other below the arcuate vein. Scale: bar equals approximately I mm. 134 M. J. HORACEK, A. M. EARLE AND J. P. GILMORE Larger vessels of the intrarenal venous system Although interlobular, arcuate and segmental arteries are accompanied by veins, the venous pattern deviates somewhat from the branching pattern of their corresponding arteries. A schematic example of the gross venous branching pattern is shown in Figure 8. Thus, although interlobular veins accompany interlobular arteries and drain into arcuate veins, the location of the veins' convergence into larger veins does not always precisely correspond with the location of arterial branching. In some cases an interlobular artery is accompanied on each side by an interlobular vein. Interlobular veins drain the adjacent cortex via venules and small veins and often receive ascending from the medulla before emptying into arcuate veins. These venules and small veins generally empty directly into interlobular veins in a perpendicular manner, although the small veins sometimes turn downwards and run parallel to an interlobular vein for a short interval before emptying into it. Occasionally a large, major interlobular vein is accompanied by a much smaller, accessory interlobular vein. Such a vein may make connections with the major vein as it travels along with it. These accessory veins drain into arcuate veins or into collecting veins which are located above or below the arcuate veins and which may be adjacent to the arcuate veins for part of their course before opening into them. Arcuate veins lie deep to the arcuate arteries and receive blood from the cortex and medulla of the kidney. They form an anastomotic network at the corticomedullary junction with other arcuate veins, so that the anterior and posterior regions of the kidney, as well as adjacent renal segments, are united by the venous system. Arcuate veins drain into larger veins of variable size that run in juxtaposition to segmental arteries, or major branches thereof, for a portion of their course. In the , these larger veins coalesce with great variation with other veins from their half (anterior or posterior) of the kidney. Generally, this coalescence results in the formation of four large prerenal veins surrounding the renal pelvis. These prerenal veins unite near the renal hilum to form the renal vein. The kidney appears to be divided into thirds by the venous system. Each third consists of both anterior and posterior halves of the kidney and is organised around an anterior and a posterior large intrarenal vein (Fig. 8). However, each third is not autonomous, since it is connected to its neighbouring third through arcuate anastomoses. The venous systems that were inspected demonstrated a good deal of symmetry between the anterior and posterior halves of the kidney.

DISCUSSION Graves (1971) indicated that the human kidney is a segmental organ. He divided the human kidney into five vascular segments and named them apical, upper, middle, lower and posterior. He further indicated that the upper, middle and lower segmental arteries are generally branches of the anterior division of the renal artery, while the posterior segmental artery is the continuation of its posterior division. The apical segmental artery has a variable origin but is usually a branch of the anterior division. Apical and lower segmental arteries supply the polar regions of the human kidney anteriorly and posteriorly. Graves also indicated that the upper and middle segmental arteries supply the parenchyma between the apical and lower segments anteriorly, while the posterior segmental artery supplies the parenchyma between these same segments posteriorly. He suggested that the upper and middle segmental arteries of the anterior division supply the parenchyma anterior to the midcoronal plane of the Renal vascular system ofmacaque monkey 135 kidney, while the posterior segmental artery supplies parenchyma posterior to the midcoronal plane. Sykes (1963) described the region of supply of the posterior segmental artery in the human similarly, except that he indicated that the posterior segmental artery does not supply all renal parenchyma posterior to the midcoronal plane between the apical and lower segments. He concluded that Br6del's line was located posterior to the longitudinal groove of the kidney. Thus he reported that the region supplied by the posterior division of the renal artery (and its continuation, the posterior segmental artery) was reduced, and that the upper and middle segmental arteries of the anterior division actually supplied posteriorly located parenchyma. Fine & Keen (1966) confirmed the presence of the arteries described by Graves (1954) but introduced the concept of primary and secondary branching of the renal artery. They indicated that the human renal artery always had branches which could be identified as posterior, upper and lower, and that these are the primary branches of the renal artery. The upper and lower branches were classified as anterior. The middle segmental artery and a previously undescribed artery, which they called the intermediate artery, were designated as secondary branches. In the vast majority of cases, both were branches of either the upper or lower primary branches. In their scheme, the apical segmental artery could either be a primary branch ofthe renal artery or a secondary branch. They described several branching patterns pertaining to the posterior, upper and lower primary branches. Possibly the most profound statement concerning renal segmentation and segmental arteries was made by Fine & Keen (1966) when they stated, "We have, however, found such variability in the volume of tissue supplied by particular branches ofthe renal artery that we were unable to define any segments of constant size, common to most kidneys. In any kidney well-defined segments exist, but in any particular kidney the extent of the segments cannot be predicted from an inspection of the outer surface of the kidney, or of its arteries in their extra-renal course. Thus, only broad generalization about the segmental arrangement of the kidneys can be made, if all kidneys are to be included." The kidneys of Macaca fascicularis and Macaca mulatta, like human kidneys, are segmental organs. Like the human kidney, these segments are variable in size and are supplied by segmental arteries with various branching patterns. Unlike human kidneys, the monkey kidneys in this study demonstrated a more symmetrical division into segments. When compared to the human kidney, the monkey's posterior division of the renal artery appears to be much more substantial, since it generally supplies the posterior halfofthe kidney. This is certainly true ifthe region supplied by the posterior segmental artery in the human kidney is as small as that described by Sykes (1963). Moreover, the polar regions ofthe monkey kidney are not dominated by the segmental arteries of the anterior division as in the human kidney, but may be supplied by either division or both divisions. Because of the extreme variability in the size of the arterial segments, the location of Br6del's line is variable. Generally, it appears to divide the monkey kidney into nearly equal halves through the midcoronal plane, although the line was never observed to have been a straight one. This is significantly different from the description of Brodel's line advanced by Sykes (1964). He describes Brodel's line as existing only in that part of the kidney situated between the apical and lower segments, and in an oblique coronal plane located posterior to the longitudinal groove of the kidney. The classification of the segmental arteries by Fine & Keen (1966) into primary or secondary branches somewhat facilitates describing the various branching patterns observed in the monkey by analogy. Thus the variable origins of the apical, middle 136 M. J. HORACEK, A. M. EARLE AND J. P. GILMORE and intermediate arteries of the monkey kidney may be partially explained on the basis of their being primary or secondary branches. Fine & Keen (1966) described three patterns into which the posterior segmental artery in the human may branch. They defined magistral, cruciate and bifurcating types of branching. With the addition of the quadripartite type advanced by the present authors it became apparent that their classification scheme was highly adaptable for describing the branching patterns of both anterior and posterior divisions of the renal artery in the monkey. Although this classification system is extremely helpful in understanding the intrarenal branching of the renal artery in the monkey, we recognise that this system is not totally reliable because of the variability encountered. We believe that the more specific a classification becomes, the more likely it is that exceptions will become apparent, and we have concluded that although there are some obvious similarities between the gross branching patterns of the renal artery in man and in the monkey, there are also several striking differences. Klapproth (1959) indicated that in dogs the renal artery divides into anterior and posterior divisions which supply anterior and posterior halves of the kidney, respectively. Each division divides into two, three or four segmental arteries in each hemisphere. In the dog, this division is highly symmetrical, there being almost perfect symmetry between anterior and posterior divisions of the renal artery. The monkey kidney is similar to the dog kidney in that the anterior and posterior divisions of the renal artery demonstrate a nearly equal area of supply. However, the anterior and posterior divisions of the monkey's renal artery may or may not display similar bran- ching patterns. Unlike the dog, there is often asymmetry between branching patterns of the anterior and posterior divisions of the renal artery. The segmental arteries of the monkey kidney branch a variable number of times and finally become arcuate arteries. The branches leading to arcuate arteries have been called , even in single-lobed kidneys. The unilobar morphology of the monkey kidney makes the term interlobar rather ambiguous and difficult to define, except to say that such branches are the branches or continuations of segmental arteries that give rise to arcuate arteries. The term is therefore not used in this paper despite conventional usage. The arcuate arteries of the monkey kidney are not always similar to the typical mammalian (including human) type described by authors in some textbooks. For example, a text by Bloom & Fawcett (1975) indicates that at the base of the medullary pyramids interlobar arteries arc to run parallel to the surface of the kidney as arcuate arteries, lying at the corticomedullary junction. Although this is generally a helpful concept that is factual in some cases, arcuate arteries in the monkey may branch at acute angles from the major branches of segmental arteries or from the continuation ofsegmental arteries in the renal parenchyma. These arcuates then penetrate the cortex and follow a path which is tangential to the corticomedullary junction before serving as the origin of interlobular arteries in the . Morison (1926) identified the problem of unconventional arcuates in humans, but indicated that the arc becomes more apparent as age advances. Christensen (1952) described the problem in dogs and could rarely identify arcuate arteries fitting textbook descriptions. However, Fourman & Moffat (1971) found arcuate arteries generally to run parallel to the surface of the kidney, thus supporting many textbook descriptions. We have concluded that arcuate arteries, like most of the renal vasculature in monkeys, are somewhat variable in form and course. Arcuate veins arch between cortex and medulla, running parallel to the surface of the kidney more consistently than arcuate arteries. One could hypothesise that this is Renal vascular system ofmacaque monkey 137 because all venous blood from renal parenchyma generally drains toward the corticomedullary junction and, therefore, veins to collect this blood are consistently needed in this region. Because these veins anastomose freely and connect all portions of the kidney, there is no division between anterior and posterior halves of the kidney with regard to the venous system. Therefore the monkey corresponds with other mammalian species in that no venous equivalent of Brodel's line exists.

SUMMARY This study was conducted on two species of monkeys, Macaca fascicularis and Macaca mulatta, to describe their gross renal vascular morphology. After death, twelve monkeys were perfused with isotonic saline to flush their vascular systems. The monkeys were then perfused either with latex or methyl methacrylate, or both, one into the arterial and the other into the venous system. The results indicated that there were six to eight arterial segments in the monkey kidney, each supplied by a segmental artery. The anterior segments were named apical, upper, middle and lower, while the posterior segments were named posterior-apical, superior, intermediate and inferior. The branching patterns of both the anterior and posterior segmental arteries were classified into one of four types: magistral, cruciate, bifurcating or quadripartite. The renal vein generally collects blood from three or four large intrarenal veins. Peripheral to this, veins accompanied arteries and were given their corresponding names. Despite this juxtaposition of veins and arteries, and the resulting convention in naming vessels, the intrarenal venous system was organised into three regions. Each region was arranged around an anterior and a posterior large intrarenal vein. The various segments of the kidney, as defined by the arterial system, were united by the arcuate veins, which anastomose throughout the corticomedullary region and drain into the large intrarenal veins mentioned above. The gross renal vascular system of the monkey was compared to, and contrasted with, human and canine renal vascular anatomy. This work was supported in part by NIH Grant No. 13427.

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