J. Anat. (1966), 100, 4, pp. 881-894 881 With 8 figures Printed in Great Britain The arteries of the human kidney BY H. FINE AND E. N. KEEN Department of Anatomy, University of Natal INTRODUCTION A study of the arrangement of the branches of the renal arteries, and the pelvis and calyces in African, European and Indian subjects has revealed a large variety of patterns. The presence of the arteries described by Graves (1954) has been confirmed but some points must be added to his description. The number of specimens was too small to reveal statistically significant racial differences. The 107 specimens were therefore considered together, as one series. MATERIALS AND METHODS Resin casts of the pelvis and calyces and the arteries of 107 kidneys (African 57, Indian 30 and European 20) were prepared. Five lobulated infant and children's kidneys were included. The ureter and vessels were injected with liquid resin, of different colours, which was allowed to set. In most specimens the arrangement of the arteries and veins outside the sinus was noted before acid digestion. The tissue around the resin was then digested in concentrated hydrochloric acid. The positions of the main branches of the renal artery in relation to the pelvis and calyces and their distribution in the parenchyma were observed. The 107 casts consisted of pairs of kidneys from 28 cadavers, and isolated kidneys from 51 other cadavers. Included in the 107 are 26 specimens with two reasonably large aortic branches supplying the kidney. Vertical gross serial sections were made through 15 additional kidneys, starting from the lateral border and working towards the pelvis. In 10 of these dyes of different colours were first injected to distinguish arteries, veins and calyces. In each the arterial distribution and the relationships between sinus, cortex, medulla, calyces and vessels were studied. Terminology. We have used the names of the branches of the renal artery introduced by Graves (1954). We have, however, found such variability in the volume of tissue supplied by particular branches of the 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 generalizations about the segmental arrangements of the kidney can be made, if all kidneys are to be included.
882 H. FINE AND E. N. KEEN PELVIS AND CALYCES Of 107 casts studied, 40 had clearly recognized upper and lower major calyces with their respective minor calyces (Fig. 1A); 35 others had upper and lower major calyces and also middle minor calyces derived from either the upper or lower A 38%/O/ C 26% B 33% D 3 Fig. 1. Patterns of pelvis and calyces (anterior view). A, Upper and lower major calyces, no middle calyces (38 %). B, Upper and lower major calyces, with middle minor calyces (33 %). C, Upper, lower and middle major calyces (26 %). D, No major calyces (3 %). major calyx, or both (Fig. 1B). Thus in 75 of the 107 casts it was easy to define clearly separate upper and lower groups of minor calyces. Twenty-eight showed middle calyces which sprang either from a third major calyx, or directly from the pelvis without clearly belonging to upper or lower
The arteries of the human kidney 883 major calyx (Fig. 1 C). In four specimens (two pairs of kidneys) the pelvis was not divided into major calyces, all the minor calyces springing directly from the pelvis (Fig. -I D). In most of the seventy-five casts with clearly defined upper and lower major calyces, an artery ran, first in the sinus and further on in the parenchyma, between the upper and lower calyces (Figs. 2, 4). This artery gave branches which supplied the mass of cortical tissue occupying the gap between the upper and lower calyces; this tissue was called the 'intermediate cortex' (Fig. 3) and the artery named the /~~~~~~~~~ 1~~~~~~~~~~~ I I / 4 0@ z Anterior % T Fig. 2. Pelvis and calyces, common arrangement (anterior-lateral view). The uppermost lower calyx faces forwards, while the lowermost upper calyx faces backwards. The position of the intermediate artery and its branches is indicated by the dotted line. 'intermediate artery' (Fig. 4). The intermediate cortex usually consisted of an oblique mass sloping from behind upwards and forwards. Sometimes it was horizontal. It bulged into the sinus in front, behind and laterally forming a narrow waist between the upper and lower major calyces, and divided the sinus into an upper and a lower compartment, like an hour-glass with an oblique, or horizontal, waist. The upper minor calyces of the lower group faced forwards and tended to lie on a plane anterior to, and either level with or above the lowest calyces of the upper group, which usually faced backwards to papillae on the posterior wall of the sinus (Fig. 2). Brodel (1901) observed a mass of cortex between the upper and lower groups of 56 Anat. 100
884 H. FINE AND E. N. KEEN calyces, but did not elaborate on it. His descriptions of the calyceal arrangement, and of the bloodless plane, do not accord with our observations. In vertical sections made at right angles to the flat of the kidney, and parallel to its long axis, the intermediate cortical masses were clearly seen in twelve of the fifteen kidneys sectioned (Figs. 3A, B). This arrangement of cortex and calyces was in accordance with the gross development of the kidney (to be described in more detail elsewhere). We have observed in five embryos (15-30 mm C.R. length) A B Sup Ant Post L S Fig. 3. Vertical antero-posterior section through kidney. A, Photograph; B, diagram. The sinus is demonstrated. The dotted line indicates the position of the intermediate cortex. that the kidney develops by fusion of an upper and a lower parenchymatous mass related to the upper and lower groups of calyces respectively. The lower half overlaps the upper half anteriorly. The lines of fusion run obliquely forwards and upwards and indicates the plane of the intermediate cortical mass with its contained branches of the intermediate artery (Fig. 3). In the twenty-eight casts where the minor calyces formed three distinct groups, an intermediate artery was nevertheless identified in twenty. In these the artery most often ran above the middle calyces, and in a few it ran down in front of a posterior-facing middle calyx. THE RENAL ARTERY AND ITS BRANCHES In most instances the renal artery was observed in the cadaver to run downward towards the hilus, where the pelvis emerges and turns down. In this way there was, medial to the pelvis, an open angle formed by the renal vessels above and the pelvis below. Whilst there were no large arteries in this angle, small ureteric vessels and veins were often seen in this position (Fig. 5).
The arteries of the human kidney 885 The primary branching of the renal artery often took place medial to the upper half of the pelvis and calyces. If not, then the primary branches were almost always seen at the hilus, before the artery reached it. Further branching took place at the hilus or in the sinus. Most primary and secondary branches transversed the sinus and pierced the parenchyma which formed its walls, but an occasional 'aberrant' branch did enter the substance of the kidney by piercing its medial aspect. Fig. 4 Fig. 5 Fig. 4. Typical cast with strongly developed intermediate and middle arteries. (The posterior artery is not labelled.) Fig. 5. Relations of renal artery and pelvis to the hilus. The suprahilar region of the kidney is demarcated. (A) Primary branches Upper artery: the vessel (or vessels, for it was sometimes represented by two or more vessels) to an anterior segment of variable extent above a line across the kidney at the level of the upper border of the hilus, but excluding the segment supplied by the suprahilar artery (see below). The upper artery frequently gave rise to the intermediate artery, the middle artery, or both. Lower artery: the vessel or vessels to a segment involving the lower end of the kidney and a variable extent of the front and the back of the organ, somewhere below a line through the middle of the hilus. The lower artery also frequently gave rise to the middle artery, the intermediate artery, or both. 56-2
886 H. FINE AND E. N. KEEN Posterior artery: a vessel, rarely duplicated, to parenchyma behind the sinus, and above the lower segment. The posterior artery rarely supplied the intermediate cortex. (B) Secondary branches Intermediate artery: this artery (not always present) has been defined on p. 883. Middle artery: a vessel (not always present) to parenchyma in front of the upper calyces of the lower group. (C) Suprahilar artery This artery was named apical by Graves (1954). We prefer the name 'suprahilar' because it is not so likely to lead to confusion with the apical branches of the upper artery, and is more descriptive of the position of the vessel. The suprahilar artery (or arteries, as it is frequently duplicated) supplied anterior and posterior parenchyma above the hilus, and generally medial to a vertical line drawn through the lateral extremity of the hilus anteriorly. This artery sometimes arose as a primary branch from the aorta or renal artery, or as a secondary branch from any of the three primary branches. THE PATTERNS FORMED BY THE BRANCHES OF THE RENAL ARTERY In this series of 107 are included 26 casts in which more than one large artery to the kidney arose from the aorta. One of the aortic branches, usually the smaller of the two, always behaved as if it were one of the primary branches of the renal artery. In 15 the separate aortic branch was a lower artery, in 8 a posterior artery, and in 3 an upper artery (Fig. 6D). In 3 casts the two arteries arising from the aorta were of approximately equal size, but in each cast one of the two arteries corresponded to one of the three primary branches. These observations have led us to regard and classify separate aortic branches as equivalent to renal artery branches with early origins. Many observers have previously reached the same conclusion. Graves (1954) attributed to Gerard (1911) priority in this observation. A renal artery always has branches which can be identified as posterior (P), upper (U) and lower (L). It will also have some or all (rarely none) of the following branches: intermediate (I), middle (M) and suprahilar. We have omitted the suprahilar artery from all our analyses as it has been adequately described by other authors, under the name 'apical artery'. As already observed the posterior, lower and upper arteries were the primary and constant branches of the renal artery. Each was duplicated, or arose as a separate aortic branch. On the other hand the intermediate and middle arteries were not always present, almost never arose as direct branches of the renal artery, and were never separate aortic branches. They were the secondary branches. The pattern of distribution of a renal artery was therefore initially determined by the way in which it divided into its three primary branches. In describing this pattern it was necessary (in order to simplify description) to regard the renal artery as giving off a first primary branch before continuing-as the renal-to divide into the other two primary branches. We held to this description even where the first primary branch appeared to be the direct continuation of the renal artery. There were four possible patterns (Fig. 6A, B, C, E), and all four were represented
The arteries of the human kidney 887 in our series. Two of the patterns, P.1 and L. 1, were common and made up 53 % and 38 % respectively of all casts. The other two patterns (U. 1 and triple) were rare, and account for less than 5 % in each case. In the descriptions which follow, separate aortic origin is included in the concept 'first branch of the renal artery', for the reasons stated earlier. The common A B 'L ll\ U U p C D R E Fig. 6. Renal artery patterns. A, P1 pattern (53 %); B, L1 pattern (38 %); C, U1 pattern (5 %); D, aortic origin of upper artery (U1 pattern); E, triple pattern (4 %). R, Renal artery; U, upper; P, posterior; L, lower; M, middle; I, intermediate. practice of regarding the renal artery as having an anterior and a posterior division was found anatomically unsatisfactory. It was not helpful in analysing the various renal artery patterns. P1 Pattern (Fig. 6A). The posterior artery was the first branch of the renal artery in 57 of 107 casts. In 8 of these the posterior was a separate aortic branch. In 26/57 the upper artery was given off as the second branch of the renal artery, which ended in the distribution of the lower artery. In 15/57 the position was L
888 H. FINE AND E. N. KEEN reversed, the lower artery being the second branch and the renal artery ending in the distribution of the upper artery. In the remaining 16/57 the renal artery ended by bifurcating into upper and lower arteries. L1 pattern (Fig. 6B). In 41/107 casts the lower artery was the first branch of the renal artery. In 9 of these the whole lower artery arose as a separate aortic branch; in a further 5 the lower artery was divided into its anterior and posterior components, the posterior arising as a separate aortic branch. In a solitary cast the anterior part was a separate aortic branch, and here the posterior artery supplied the whole of the back of the lower part of the kidney, replacing the posterior branch of the lower artery completely. In these 41 L1 casts the lower artery was formally regarded as the first branch of the renal artery, which continued to divide into posterior and upper arteries in the following way. In 29 the termination of the renal appeared to be the upper artery, in 8 the renal artery bifurcated, and in the remaining 4 the renal artery ended as the posterior artery. UT pattern (Fig. 6 C). In 5 of the 107 casts the upper artery was either a separate aortic branch 3 casts, or the first branch of the renal artery-2 casts. In all 5 the renal artery then gave off the posterior branch and ended as the lower artery. Triple pattern (Fig. 6E). In 4 of the 107 casts the renal artery divided into its three primary branches at one point. DESCRIPTION OF THE BRANCHES OF THE RENAL ARTERY Posterior artery The posterior artery was present in all casts and was usually a single uncomplicated branch. In 2 only (of 107) was it duplicated, arising as upper and lower branches from the renal artery in an L1 cast. In one other L1 cast the posterior artery gave off a large branch to the intermediate cortex from the back, and a similar branch was given off by the upper posterior in one of the duplicate cases. We considered these two unusual branches to be intermediate arteries. The point of origin of the posterior artery was extrahilar in 80 % of casts, and seen at the hilus in the rest except in a solitary cast, where the artery arose in the renal sinus. The artery normally arose medial to the upper border of the pelvis, and ran laterally behind the pelvis to enter the sinus. Here the posterior artery crossed the back of the upper major calyx in 670 of casts. It lay behind the upper half of the pelvis in all the others except two, where it was seen to ramify before reaching the medial edge of the pelvis. The mode of branching of the posterior artery usually formed one of two common patterns (Fig. 7). These were (i) mnagistral (5000) where the artery curved down towards the lower pole (Graves, 1954), giving off successive branches upwards, laterally, and downwards; and (ii) bifurcating (3000) where the artery divided into two more or less equal-sized branches running up and down respectively. In 10,o (cruciate) the artery ran straight across the back of the pelvis and calyces, giving vertical upper and lower branches. The pattern in the remaining casts was not classified; these were mostly cases of suppression of the posterior distribution in the lower part of the kidney (see below).
The arteries of the human kidney 889 Magistral 50%/o Bifurcating 30%Y Cruciate I el4 Fig. 7. The three common posterior artery patterns. A, Magistral pattern; B, bifurcating pattern; C, cruciate pattern. A B U'U CD Fig. 8. Variation of renal arterial segments (lateral view). A, Upper segment large, intermediate segment extending downwards, posterior segment of average size. B, Upper segment large, intermediate segment extending backwards and downwards, posterior segment reduced. C, Upper segment small, intermediate segment absent, posterior segment large. D, Upper and posterior segments large, intermediate and lower segments small. I, Intermediate segment; L, lower segment; M, middle segment; U, upper segment; P, posterior segment.
890 H. FINE AND E. N. KEEN The segment of the kidney supplied by the posterior artery varied greatly (Fig. 8 B and C), from a restricted part of the back of the upper half of the kidney, to the whole of the back half of the kidney including an equal share of both upper and lower ends. We classified ninety-nine casts in which the distribution of the artery could be accurately delineated in the following way: Small posterior segments (15 %0) (Fig. 8 B). In these casts the distribution of the posterior artery was restricted in one of three ways: (a) confined to a small area on the back of the upper half of the kidney, being excluded from the rest of the back by a large intermediate artery and the lower artery; (b) confined to the middle zone, being excluded from both ends by the upper and lower artery distribution; or (c) split into two separate distributions by the intrusion of a large intermediate artery into the posterior parenchyma. Medium posterior segments (35 %0) (Fig. 8A). In these casts the distribution of the posterior artery did not reach as far forwards as the lateral border of the kidney. While these casts recalled Brodel's (1901) classical description, it must be observed that the boundary line between the posterior segment and the distribution of the other renal artery branches varied widely, being often curved, sinuous or irregular. We are thus unable to support Brodel's contention about the regular occurrence of a relatively bloodless plane. Large posterior segments (50 %) (Fig. 8 C, D). The branches of the posterior artery reached at least as far forwards as the outer border of the kidney, and often were seen to encroach on anterior parenchyma, the cast being inspected on edge, i.e. from its lateral aspect. Considering all the casts, the upper end of the kidney was equally shared between posterior and upper arteries in 48 %, and branches of the posterior supplied parenchyma on the front of the upper end in 9 %. The lower end of the kidney is regularly supplied, front and back, by the lower artery. However, in 9 0 of casts this region was equally shared by posterior and lower arteries (Fig. 8 D), and in a solitary cast branches of the posterior artery were seen to supply the front of the lower end. In the middle regions of the kidney, branches of the posterior artery supplied anterior parenchyma, passing forwards beyond the outer border, in 20 % of all casts. Lower artery The five casts in which the lower artery was duplicated through the aortic origin of a posterior lower artery have already been mentioned. In one other P1 cast the lower artery arose as two separate branches. Thus all or part of the lower artery came directly from the aorta in 15/107 cases, and the artery was duplicated in six. In 34 of the 107 casts the lower artery was uncomplicated, i.e. not associated with middle or intermediate arteries. In 45/107 casts the lower artery gave a branch sufficiently distinct and large to be called a middle artery. In only one cast did the lower end as the middle artery; in two others it ended in a bifurcation of middle and lower arteries. In the remaining 28 casts the lower artery had associated with it the intermediate artery; in 15 of these a middle artery was also a branch of the lower, either from the artery itself or from its intermediate branch. In only 6 of the 28 casts did the lower artery terminate as the intermediate artery; in 5 others the lower artery ended
The arteries of the human kidney 891 in a bifurcation of intermediate and lower arteries. In summary, in 107 kidneys the lower arteries gave rise to 60 middle arteries and 28 intermediate arteries; 15 lower arteries had both, and 34 had neither. The point of origin of the lower artery was extrahilar in 80% of casts. In the rest it was seen at the hilus, being concealed in the sinus in only two casts. Arising medial to the upper part of the kidney, the lower artery ran obliquely down in front of the pelvis to its lower border, which it almost always crossed. In a small number the artery remained anterior to the lower major calyx, and in four of the six where the lower artery was duplicated, one branch passed below and one lay in front of the lower major calyx. In 80 % of the casts the lower artery divided into anterior and posterior branches (Graves, 1954), usually late in its course. (In the others only a large anterior lower artery was identified, usually giving off branches to posterior parenchyma at the lower end of the kidney.) The two branches supplied the lower end of the kidney, as well as varying additional amounts of parenchyma on the front and back of the lower part of the kidney. It was possible to define the precise extent of the lower segment in ninety-seven casts. In 60 % the lower segment was either more extensive in front of the lower end than behind it, or even excluded from the back of the lower end of the kidney by a large posterior segment (ten casts). In about 30 % the lower segment included approximately equal amounts of kidney substance on both aspects of the lower end. In only six casts was the lower segment more extensive posteriorly than anteriorly. The lower segment seemed less variable than those of the other branches. In the 97 casts it was judged unusually large in 6, and unusually small in a like number. In 10 it was limited to the front of the kidney. In the remaining 75 the lower segment had its usual shape, position and size. Upper artery Apart from suprahilar arteries, which were frequently multiple, the upper artery was duplicated in 11/107 casts, usually arising as two sizeable branches from an artery ending as the intermediate artery. In 50 of the 107 casts the upper artery was uncomplicated, i.e. not associated with intermediate or middle artery. In 50 casts the upper artery was combined with an intermediate artery; in 34 of the 50 the upper artery clearly continued as, and ended by becoming, the intermediate artery after it had given off apical and/or lateral branches to the upper end of the kidney anteriorly. (In 9/50 it gave off the intermediate artery before continuing its own distribution, and in 7 others the upper artery ended in a bifurcation of upper and intermediate arteries.) In 14 of the 50 casts a middle artery was also a branch, either of the intermediate or of the upper itself before its intermediate branch. In 7 casts a middle artery was combined with the upper artery in the absence-of an intermediate branch of the upper. In 4/7 it was a downward branch of the upper artery; the middle artery formed the frank termination of the upper artery in 2/7 casts, and the upper ended in a bifurcation of upper and middle arteries in a solitary case. In summary, in 107 kidneys the upper arteries gave rise to 50 intermediate arteries and 21 middle arteries; 14 upper arteries gave off both, and 50 neither. The point of origin of the upper artery was extrahilar in 80 % of specimens. The
892 H. FINE AND E. N. KEEN origin could be found at the hilus in all the rest save three, where it was hidden in the sinus. The artery coursed upwards medial to the pelvis and upper major calyx in 73 % of all casts. In 16 % it crossed the upper major calyx, usually near its origin from the pelvis, and ramified lateral to the calyx. In the remaining casts the artery was either directly in front of the upper major calyx or divided into two branches with different positions. The extent of the upper artery segment was very variable (Fig. 8). It always involved anterior parenchyma in the upper part of the kidney, and usually extended to the upper pole. In 43 % of all casts the upper artery also supplied posterior parenchyma, displacing the posterior segment at the upper end. In 9 % the situation was reversed, the upper segment being reduced by anterior branches of the posterior artery (q.v.). The size of the segment varied from less than one-third of the anterior parenchyma above the hilus to as much as the front of the upper half of the kidney (rare). Small upper segments are complementary with large suprahilar segments medially, and extensive middle or intermediate artery segments below. Intermediate artery The intermediate artery was identified in 81 of the 107 casts. It was combined with the upper artery in the majority 50/81. In these 50 the three primary branches thus became the posterior, lower and upper-intermediate arteries. This arrangement we have called the type 1 origin of the intermediate artery. (Graves (1954) used this nomenclature to describe the origin of the middle artery.) The termination of the upper/intermediate artery is described on p. 891. The intermediate artery was combined with the lower artery in a large minority of cases 28/81. This we called the type 2 origin of the intermediate artery. The termination of the lower/intermediate artery is described on p. 890. The two unusual intermediate arteries which are branches of posterior arteries have been mentioned on p. 888. In one L1 cast the intermediate was given off as the second branch of the renal artery, after the lower artery. This arrangement was unique in our series. The origin of the intermediate artery was extrahilar in 25 %/0, or seen at the hilus in 30 % of the kidneys in which it was present. In 45 % its origin was hidden in the sinus. In the sinus the intermediate artery ran laterally across the front of the pelvis on its way to the intermediate cortex. In 90 % of casts it was seen crossing the upper half or middle of the pelvis, or upper major calyx; in only 10 % did it cross the lower half of the pelvis. The artery left the sinus to enter the intermediate cortex, and in the casts was seen to occupy the gap between the upper and lower, or upper and middle, groups of calyces. The intermediate artery supplied cortex and medulla related to the adjacent minor calyces of the upper and lower (or middle) groups, and frequently had a branch running down between the anterior and posterior rows of the lower group of calyces (see Fig. 2). We did not observe a similar vertical branch running among the upper calyces. In seventy-three casts it was possible to define the whole extent of the intermediate artery segment. Its size varied markedly (Fig. 8). It was bounded by the
The arteries of the human kidney 893 upper segment above, by the middle segment (where present) or the lower segment below, and the posterior segment behind. It was frequently overlapped in front by the middle or lower segment. The variability of the segment depended on how far backwards or downwards the intermediate artery penetrated. In a few instances it supplied a large part of the back of the kidney, splitting the posterior segment into two small parts (Fig. 8B). In a few others the artery ran down between the lower calyces almost to the lower end of the kidney. In 27 of the 73 the segment extended appreciably in both directions. In 13 others it extended backwards but not downwards, and in another 13 downwards without reaching the back of the kidney. In the remaining 20 the intermediate artery showed neither tendency, being limited in its distribution to the upper and anterior part of the intermediate cortex (Fig. 8D). In twenty-six casts no intermediate artery was identified (Fig. 8 C). In all but two of these a middle artery was seen. Thus in only 2 of the 107 casts were the major branches of the renal artery limited to the three primary branches. Middle artery The middle arterv was identified in 81 of 107 casts. In 5-7 of these an intermediate artery was also present, while in 24 the middle artery was the only secondary branch. In only 2 casts were both intermediate and middle arteries absent. The middle artery was a branch of the lower artery in 53 of the 81, and a branch of a type 2 intermediate artery (itself a branch of the lower artery) in 7. The termination of the lower artery is described on p. 891. Much less frequently the middle artery was a branch of the upper artery (13/81) or of a type 1 intermediate artery (8). The termination of the upper artery is described oin p. 891. The origin of the middle artery was extrahilar in 7, seen at the hilus in 36, and concealed in the sinus in 38. It will be seen that in more than half the cases where it was present it was possible to find the origin of the middle artery outside the sinus. The middle artery usually ran across the front of the lower half of the pelvis and calyces. When it was a branch of the upper artery, and sometimes when it was a branch of the intermediate artery, its course was downwards and laterally. With an origin from the lower artery, and sometimes with a low origin from an intermediate artery, the middle artery ran more or less horizontally across the pelvis. With one exception, it was situated below the intermediate artery, where both were present. In three instances only was the middle artery situated in front of the upper half of the pelvis and calyces (here the lower group of calyces occupied more of the kidney than usual); in ten it lay in front of the middle of the pelvis. In all the rest it was found in its usual position across the front of the lower half of the pelvis and calyces. It must be pointed out that the identification of a middle artery often involved a marginal decision about the status of the first laterally directed branch of the lower artery. If sufficiently large and distinct it was labelled 'middle', provided it supplied the typical middle segment. The middle artery segment lies in front of the upper calyces of the lower group. Occasionally the artery gave branches supplying posterior parenchyma and inter-
894 H. FINE AND E. N. KEEN digitating with the distribution of the posterior artery. There was never a downward extension of the middle artery segment of the kind frequently seen in the distribution of the intermediate artery. SUMMARY The arrangements of the pelvis and calyces, and the arteries were studied in 107 casts, and in 15 vertically sectioned kidneys. In 75 of the 107 the pelvis and calyces were arranged in two parts-upper and lower. In 35 of the 75, middle calyces, from upper or lower major calyx, or both, were seen. In the remaining 28 casts the calyces were clearly in 3 groups. A mass of cortical tissue below the upper calyces contained the intermediate artery and its branches. The usual arrangement of a kidney was an upper and lower part joined by the intermediate cortex. The upper major calyx drained the upper part, and the lower major calyx the lower part. The lower part of the kidney overlapped the upper part anteriorly; the line of fusion sloped from the front backwards and downwards. Thus the uppermost lower calyces drained papillae on the anterior wall of the sinus, and lowermost upper calyces usually drained posterior papillae, often at the same level. A concept of primary and secondary branching of the renal artery has been introduced. The renal artery divided into three primary branches (posterior, lower, upper) in two common and two uncommon ways. Two secondary branches (intermediate and middle) were sufficiently constant to warrant description, apart from the suprahilar (apical) artery, which could be primary or secondary in its origin. The course, position and variations in segmental supply of the primary and secondary branches have been described. The two common patterns of primary branching were labelled P1 and L1 (after the first branch of the renal artery). When combined with the type of origin of the intermediate artery (type 1 with the upper artery, type 2 with the lower artery) the common arrangements were found to be P1 type 1, and L1 type 1. P1 or L1 type 2 were less common. Other arrangements were rare. The authors are indebted to Mr E. W. Williams for his assistance in the preparation of the casts. REFERENCES BRODEL, M. (1901). The intrinsic blood vessels of the kidney. Bull. Johns Hopkins Hosp. 12, 10-18. GERARD, G. (1911). Les arteres r~nales (note statistique d'apres l'6tude de 150 paires de reins). J. Anat. Physiol., Paris, 47, 531-534. GRAVIES, F. T. (1954). The anatomy of the intrarenal arteries and its application to segmental resection of the kidney. Br. J. Surg. 42, 132-139.