The Blood Supply of the Lumbar and Sacral Plexuses in the Human Foetus* by M

Home , Lumbar nerves, Median sacral artery

J. Anat., Lond. (1964), 98, 1, 105-116 105 With 4 plates and 3 text-figures Printed in Great Britain The blood supply of the lumbar and sacral plexuses in the human foetus* BY M. H. DAYt Department of Anatomy, Royal Free Hospital School of Medicine

INTRODUCTION The existence of a blood supply to peripheral nerve is well established. Recently, a number of authors have reviewed the literature of the field, among them Blunt (1956) and Abdullah (1958), who from their own observations have confirmed that peripheral nerves are supplied by regional vessels reinforcing longitudinally arranged channels which freely anastomose with each other. There is also evidence that posterior root ganglia are particularly well supplied with blood vessels (Abdullah, 1958), but the precise distribution and arrangement of arteries to some individual nerve trunks and plexuses is still in need of investigation. The literature reveals few references to the blood supply of the lumbar and sacral plexuses. The distribution of arteries to the roots and ganglia of the sacral nerves was noted by Haller (1756), but the most important contributions in this field were those of Bartholdy (1897) and Tonkoff (1898), whose observations on the lumbar and sacral plexuses form part of a general survey of the blood supply of peripheral nerve in man. They cited the lumbar, ilio-lumbar, median and lateral sacral arteries as well as the gluteal and pudendal vessels as sources of supply, but gave no indication of the frequency of these contributions. Subsequent authors including Hovelacque (1927), dealt briefly with the distribution of the lateral sacral, median sacral, gluteal and pudendal arteries to the sacral plexus, but treated more fully the blood supply of the sciatic nerve. Although Adachi (1928), described the distribution of the intra-pelvic arteries in some detail, he made no reference to the blood supply of nerves. It appears that there is nowhere a fully documented account of the blood supply of the lumbar and sacral plexuses, and accordingly a re-assessment of the matter has been undertaken. The problem is of anatomical interest and may be of clinical significance, since ischaemic damage to nerve has been reported in obliterative vascular disease (Roberts, 1948), cryopathy (Denny-Brown, Adams, Brenner & Doherty, 1945), peripheral nerve injuries (Richards, 1954) and nerve compression syndromes (Bowden & Gutmann, 1949).

MATERIALS AND METHODS Material was obtained from 18 stillborn foetuses of ages ranging from 18-40 weeks, from one neonatal autopsy, and from an adult. * The results of this investigation were presented as part ot a thesis for which the degree of Ph.D. was awarded by the University of London in May 1962. t Present address: Department of Anatomy, The Middlesex Hospital Medical School, London, W. 1. 106 M. H. DAY In 15 foetuses Neoprene rubber latex, diluted with distilled water to produce a 75 % solution, was injected through the descending thoracic aorta; in 7 cases red dye was added to the solution, and in 8 India ink. Fourteen of the foetuses were injected using a manometrically controlled injection apparatus, and one by means of a hand syringe. The injection pressures were limited to 100 mm. Hg in foetuses over the age of 20 weeks and to 80 mm. Hg under that age; the injections were judged to be complete when small skin vessels of the back and feet were filled with the injection mass. The systemic venous system of one 20-week foetus was injected through the right atrium with rubber latex and India ink at a maximum pressure of 50 mm. Hg. Following injection, the lumbar spine, sacrum and pelvis were removed en bloc and fixed in 10 % formalin for 3-4 weeks. The lumbar and sacral plexuses and their blood vessels were dissected with the aid of operating spectacles and a dissecting microscope. When the intervertebral foramina were reached lam- inectomy was performed and the contents of the intervertebral canals exposed by nibbling away the pedicles of the vertebrae. Finally, the dura mater and the arachnoid were opened to expose the spinal cord and the cauda equina. After complete dehydration in graded alcohols and chloroform the specimens injected with rubber latex and India ink were cleared in tetrahydronaphthalene (Torr, 1957), to reveal the finer vessels and obtain a three dimensional view of their distribution. The intrinsic vascular arrangements were studied histologically in one adult, and in 3 foetuses whose ages ranged from 22 to 31 weeks. Blunt's modification of Pick- worth's method (sodium nitroprusside benzidine stain), MacConaill's FALG and MG blue methods (MacConaill & Gurr, 1960), and the FALGOSE method (MacConaill, 1961), were used. RESULTS The lumbar and sacral plexuses of nerves obtain their blood supply from the nearest available vessels, all of which originate indirectly from the abdominal aorta. The arterial blood supply of the roots and ganglia of the lumbar and sacral nerves The first to the fourth lumbar nerves may be grouped together, as a similar pattern of supply was found at each of these segmental levels. Lumbar spinal arteries commonly arose from the posterior division of the lumbar artery, and entered the intervertebral foramen in relation to the segmental nerve. The arteries supplying the nerve roots and ganglia were derived from the lumbar spinal arteries or, much less frequently, from the corresponding lumbar arteries directly. The segmental pattern of blood supply shown for the upper four lumbar nerves was interrupted caudally at the level of the bifurcation of the aorta. Fifth lumbar arteries were present on both sides in 9 of 15 foetuses. On the left the fifth lumbar nerve roots and ganglia were supplied by the lumbar artery through its spinal branch in nine cases and by the ilio-lumbar artery in the other six. On the right side the fifth lumbar nerve roots were supplied by the fifth lumbar spinal artery, the fifth lumbar artery, the ilio-lumbar or the superior gluteal artery in the ratios of 4:2:8:1. The right fifth lumbar ganglia were supplied by the same group of vessels in the ratios of 3:2:9:1 (Table 1). Blood supply ofplexuses in human foetus 107 As in the lumbar region, the vascular supply of the sacral roots and ganglia was basically segmental (Text-fig. 1). The lateral sacral artery supplied the sacral nerve roots in 38 of 55 roots of the left, and in 37 of 62 on the right side. With regard to the other vessels involved, on both left and right sides, the superior gluteal arteries were responsible for the supply of the sacral roots (left 12/55, right 10/62); less commonly the supply to the roots came from inferior gluteal artery (left 8/55, right 3/62), the ilio-lumbar artery (left 4/55, right 3/62), the median sacral artery (left 1/55, right 7/62) and the internal iliac arteries (left 2/55, right 2/62). The sacral ganglia were supplied by the lateral sacral artery 34/56 times on the left side and 37/61 times on the right side; the superior gluteal artery supplied the ganglia (left 12/56, right 10/61), less commonly the supply came from the inferior gluteal artery (left 8/56, right 3/61), the ilio-lumbar artery (left 4/56, right 3/61, the median sacral artery (left 1/56, right 5/61) and the internal iliac artery (left 2/56, right 3/61).

Text-fig. 1. The left side of the true pelvis of a full-term foetus, showing the distribution of arteries to the ventral rami forming the sacral plexus. (Drawn from an injected specimen.)

When these results were combined and tabulated (Table 1), it was clear that vessels which were not segmental in origin tended to be distributed over a group of successive segments. Thus the superior gluteal artery was distributed to the roots and ganglia of the fifth lumbar to the third sacral segments (inclusive), whilst the inferior gluteal artery was distributed to the corresponding structures from the second to the fourth sacral segments. Table 1 demonstrates that the roots and ganglia between the 108 M. H. DAY fifth lumbar and the third sacral segmental level received their arteries from a variety of sources, but there appeared to be neither profusion nor poverty of blood supply to any nerve, or group of nerves, in this region. The arrangement of the lumbar and sacral spinal arteries Three principal groups of branches were derived from each spinal artery or its parent stem. These included branches to the vertebrae, the posterior root ganglia and the nerve roots. Branches to the vertebrae. At each lumbar and sacral segmental level a vertebral branch arose and passed through the intervertebral foramen anterior to the segmental nerve roots. This branch divided into superior and inferior subdivisions which anastomosed with vessels entering foramina both cephalic and caudal to it, as well as with vessels from the opposite side. These arteries were distributed to the vertebral bodies forming an anastomotic network on the anterior wall of the spinal canal. (Pls. 1-3). Branches to the ganglia. These arteries arose from the posterior divisions of the lumbar arteries or from lumbar spinal arteries, in a plane posterior to the vessels to the vertebrae and ran directly to the ganglia. In the sacral region, branches to the ganglia originated from vessels supplying the intra-spinal portion of the nerve roots, these latter vessels arose from the spinal branches of the sacral segmental vessels. This alteration in the basic pattern resulted from changes in the positions of the ganglia at different levels (see below). Arteries entered the ganglia by piercing their sheaths at the poles or the equatorial region; other vessels did not pierce the ganglion sheath but continued over its surface to supply the dural root sleeves and the spinal dura (Text-fig. 2). These dural vessels anastomosed with branches from adjacent segments of both the same and opposite sides. Branches to the nerve roots. In the lumbar region these arteries were derived from the posterior divisions of the segmental arteries. Having crossed the ganglia they entered the dural root sleeves by piercing the dura mater and continued along the anterior and posterior nerve roots. In the sacral region the corresponding vessels ran up with the intra-spinal nerve roots distal to the ganglia, gave rise to the ganglionic branches and then continued cranially to supply the nerve roots proximal to the ganglia. The radicular arteries of the cauda equina were markedly tortuous and convoluted. The positions of the lumbar and sacral posterior root ganglia There appeared to be two basic patterns of distribution of the branches of the spinal arteries which were related to the dispositions of the ganglia with respect to the intervertebral foramina. In fourteen foetuses the sacral ganglia were within the spinal canal, but the first lumbar ganglion was outside the spinal canal. Between the second lumbar and first sacral segments (inclusive) the positions of the ganglia were variable. When all levels were considered 176/280 ganglia were within the spinal canal, 76/280 outside and 28/280 were in an intermediate position half in and half outside the spinal canal. Caudal to the first sacral segment the roots of nerves showed a progressive increase in the length of their post-ganglionic portions. This increase was occasioned Blood supply of plexuses in human foetus 109 No. of q0=m It1C4 CO l C kktoi = t-Co -00t = = = &c i 0 0 o observations F-4 P-4 r-( P-4 " _"H "4H"4~ "I" 4 " ^ _4F4P - - 1 r4rqP4 r.

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ff ^ " 9" C X mN 4 tZ t4q 110 M. H. DAY by changes in the segmental level of the ganglia. In 8 full-term foetuses no ganglia were found caudal to the third sacral segment. The distribution of arteries to the lumbar and sacral ganglia The distribution of arteries to the lumbar and sacral ganglia is set out in Table 1. The first, second, third and fourth lumbar ganglia generally obtained their blood supply from the lumbar segmental arteries, most commonly from their spinal branches. The fifth lumbar ganglion was supplied by the ilio-lumbar (15/30) or fifth lumbar spinal artery (12/80); less frequently the fifth lumbar (2/80) or superior gluteal artery (1/30) was responsible for the supply of this ganglion.

ARadicular artery

Branches to ~~ iI second lumbar root sleeve rootsleeve ~...(..~ (post. divn.)

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Text-fig. 2. The right second lumbar ganglion of a 28-week foetus, showing the ganglionic, radicular and dural arteries. (Drawn from an injected specimen.)

The first sacral ganglion was usually supplied by the superior gluteal artery (13/32), less commonly by the lateral sacral (7/32), ilio-lumbar (6/32), internal iliac (5/32) or median sacral arteries (1/32). Caudal to the first sacral spinal nerve the lateral sacral artery generally supplied the sacral ganglia, less frequently these ganglia were supplied from the superior gluteal, inferior gluteal and median sacral arteries (Table 1). The distribution of arteries to the nerves forming or arising from the lumbar and sacral plexuses At the intervertebral foramina the ventral rami received arteries which ran in the epineurial tissues and sank into the nerve trunk to contribute to the intrinsic longitudinal vascular channels (Text-fig. 3). The arteries to the first, second and third lumbar ventral rami invariably arose from the corresponding segmental artery, either directly from the main trunk or indirectly from its spinal branch. At lower Blood supply of plexuses in human foetus 111 levels the vessels which supplied the roots and ganglia also contributed to the supply of the lumbar and sacral nerves and plexuses. Where the ventral rami united to form the lumbar and sacral nerve plexuses, and branches were formed, it became increasingly difficult to assign arteries to individual nerve trunks. At these points of union, arteries commonly entered the nerves (Text-fig. 3; PI. 4, fig. 10).

Third lumbar artery

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Text-fig. 3. The left lumbar region of a full term foetus showing arteries entering the lumbar plexus at the points of union of the ventral rami, also ganglionic and radicular vessels. Quadratus lumborum has been dissected to expose the posterior aspect of the lumbar plexus. (Drawn from an injected specimen.)

In the lumbar region the largest proportion of vessels supplying ventral rami and nerve trunks were derived from the lumbar arteries, (left side 61/108; right side 57/88), other vessels noted included the lumbar spinal, ilio-lumbar and superior gluteal arteries. In one specimen the obturator artery supplied the fourth lumbar nerve. In the sacral region the lateral sacral arteries supplied the ventral rami forming the sacral plexuses on 27/60 occasions on the left and 29/59 on the right side. The difficulty of allocating vessels to individual nerve trunks recurred in the sacral region. Other vessels observed supplying the sacral ventral rami included the superior gluteal, inferior gluteal, median sacral, internal iliac, ilio-lumbar and pudendal arteries in descending order of frequency. In this investigation no arteries to the lumbar and sacral plexuses were found to arise from the common iliac, external iliac or umbilical arteries. 112 M. H. DAY

The venous drainage The systemic veins of one foetus were injected with rubber latex and India ink; subsequent clearing revealed the venous pattern of the lumbar and sacral regions. Striking confirmation was obtained of the density of the internal vertebral venous plexus. The number of veins present was so great that it was impossible to trace their precise arrangements. However, it was clear that communications existed at all levels between the internal and external vertebral venous plexuses through the lumbar and sacral intervertebral foramina. Intrinsic vascular arrangements In general the intrinsic vessels of the lumbar and sacral nerve roots, ganglia and ventral rami conformed to previous descriptions (P1. 4). In the posterior root ganglia examined, vessels which entered at the poles or the equatorial regions com- municated with each other and contributed to the longitudinal vascular channels which ran centrally through the ganglia. The peripherally placed ganglion cells were absent at the point of entry of an equatorial vessel when this vessel joined the longitudinal channels. The vessels which supplied the lumbar and sacral plexuses were frequently observed to enter at the points of union of the ventral rami (P1. 4, fig. 10) and divide to run both centrally and peripherally within the plexuses, becoming continuous with the longitudinal channels within the nerve roots and nerves (PI. 4, fig. 7).

DISCUSSION The methods used in this study consist basically of an arterial injection followed by a technique of visualization, such as dissection or clearing. Unless carefully controlled with regard to pressure, the physical characteristics of the mass and the degree of filling of the vascular system, injection methods are open to criticism. Furthermore, demonstration of vascular channels by an anatomical technique is not direct evidence that blood flows through these channels, nor is the direction of flow during life, made apparent. Little work has been published on the dynamic aspects ofthe blood supply ofnerve. Failure to demonstrate vessels by means of Pickworth's or MacConaill's methods may be due to lack of blood within vessels, thus there is a need for more refined techniques to show the entire vascular network of nerves and ganglia. In general, the segmental pattern of arteries supplying the lumbar and sacral plexuses described by previous authors (Sappey, 1877; Quain, 1897; Bartholdy, 1897; Tonkoff, 1898; Testut, 1911; Poirier & Charpy, 1912; Hovelacque, 1927) has been confirmed in the human foetus, and the pattern of distribution of the spinal arteries and the vasa nervora has been investigated. The incidence of individual vessels in the supply ofthe lumbar and sacral plexuses has been shown in the material examined. From this investigation it appears that the arterial blood supply of human foetal lumbar and sacral plexuses is extensive and shows a striking bilateral symmetry (Table 1). The distribution of vessels to the nerve roots and ganglia of the fifth Blood supply of plexuses in human foetus 113 lumbar segment is exceptional (Table 1). The arteries of the left side arise from the fifth lumbar spinal artery or the ilio-lumbar artery; whereas on the right side the arteries arise either from the fifth lumbar spinal artery, the fifth lumbar artery, the ilio-lumbar artery or the superior gluteal artery. This asymmetry of distribution might be related to the position of the abdominal aorta at its bifurcation. The vessels which supply the lumbar and sacral plexuses have widely separated origins, as a result of the segmental arrangement, depending directly or indirectly, upon the abdominal aorta. A segmental arrangement has particular advantage when the structure supplied extends over several segments and possesses internal anastomoses; occlusion of one or more segmental vessels might not prove disastrous. In the lower lumbar and upper sacral regions a variety of vessels of differing origins fill the gap in the segmental pattern; despite this variability no evidence has been found that these nerves have a better or a poorer blood supply than the nerves of other levels. The arrangement of the lumbar and sacral spinal arteries is related to the dispositions of the posterior root ganglia. In the adult, Testut (1911) situates the lumbar ganglia in the intervertebral foramina whilst the sacral ganglia are in the sacral canal, the coccygeal ganglion being inconstant. Soulie (1912) reports similar findings. In the group of foetuses examined the positions of the ganglia differ from those previously reported in the adult in that the first lumbar ganglion is invariably outside the spinal canal, whereas caudal to the first sacral segment the sacral ganglia are invariably within the spinal canal. Between the second lumbar and first sacral segments (inclusive) the position of the ganglion is variable. This disparity is probably due in part to differential growth of the spinal cord and nerve roots with respect to the vertebral column, and may be related also to the positions of the trunk and limbs when the observations are made upon the roots and ganglia. Some account has been taken of the latter point and the results will be presented separately. As illustrated by Quain (1844), vessels are found to ramify on the posterior aspect of the vertebral bodies. These branches form an anastomotic network based upon a segmentally arranged diamond pattern, which persists caudally despite the changing positions of the posterior root ganglia. These vessels are mentioned by Gillilan (1958) and attributed to the anterior spinal rami; in this series these vessels are inconstant in their origins. Associated with the branches to the ganglia are vessels which do not enter the ganglia, but continue over their surfaces to supply the dural root sleeves and the spinal dura, similar to those seen by Abdullah (1958) in the cervical region. Radicular vessels also cross the ganglia and enter the dural root sleeves, continuing along with the anterior and posterior nerve roots. In the cleared material these vessels were markedly tortuous (PI. 3, figs. 3, 4), as shown by Breig (1960). This may be due in part to differential shrinkage during dehydration and clearing, on the other hand tortuosity may allow the nerves to stretch without endangering the integrity of their blood supply. For the most part the histological material confirms the findings of previous authors in particular those of Bergmann & Alexander (1941) and Abdullah (1958). In the preparations of posterior root ganglia examined, no evidence has been found 8 Anat. 98 114 M. H. DAY of the irregular capillary dilatations reported by Bergmann & Alexander (1941) in adults (24-84 years), Blunt (1956) in the geniculate ganglion of subjects aged 14-85 years and Abdullah (1958) in the cervical posterior root ganglia of adults (56-60 years). This is not easily explained. It has been suggested (Bowden, 1961) that these capillary dilatations may result from death of cells in posterior root ganglia. In this event the number of dilatations observed may increase with the age of the subject. In this small series the majority of ganglia have been taken from the lumbar and sacral regions of foetuses. No evidence has been found of the arcuate vessels described by Abdullah (1958), but the vascular patterns of roots, ganglia and nerves reported by this author in the cervical region, is confirmed in the lumbar and sacral regions. It may be of significance that vessels which supply nerve roots, dural root sleeves and posterior root ganglia are closely related to each other in the intervertebral foramina. This restricted space is bounded by structures prone to degenerative and proliferative changes. Herniation of the nucleus pulposus of a degenerating intervertebral disc (Mixter & Barr, 1934), osteoarthritis of the spine (Putti, 1927), hypertrophy of the ligamenta flava (Towne & Reichert, 1931) and osteoarthritis of the neurocentral joints (Cave, Griffiths & Whiteley, 1955), are all conditions where there is encroachment upon intervertebral foramina. Constriction of the contents of the foramina might be sufficient to diminish the blood flow to the nerves and meninges to the point of ischaemia, either by direct pressure upon arteries or by the occlusion of veins leading to oedema and secondary ischaemia.

SUMMARY 1. Observations have been made upon 30 lumbar and sacral plexuses from 15 foetuses and one neonate, injected with Neoprene rubber latex; and upon one adult and three foetuses using histological methods. 2. The basic segmental arrangement of the arterial blood supply has been confirmed and the origin, incidence and distribution of vessels to the individual roots, ganglia and nerves demonstrated. 3. Variability of the arteries supplying the fifth lumbar to the third sacral segment is shown. 4. Confirmation is obtained of the density of the internal vertebral venous plexus in the human foetus. 5. The intraneural vascular patterns previously shown in other regions, is confirmed in the lumbar and sacral regions by histological studies of the roots, ganglia and nerves; the present findings differ in detail from previous reports.

It is with great pleasure that I acknowledge the advice and encouragement received from Prof. Ruth E. M. Bowden. I am indebted to Prof. K. R. Hill and his staff, Miss J. A. M. Moore, Dr Husain, Dr Ramsay and Dr Haram for material. I am very grateful to Miss Frances Ellis, Mr R. Fletcher, Mr G. Burnard, and Miss Dibden for the photographs; to Mrs Audrey Besterman for the drawings and to Mr L. Grayson, Miss I. Johnson and the late Mr W. Matthews, for valuable technical assistance. Journal of Anatomy, Vol. 98, Part 1 Plate 1

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Al. H. DAY Blood supply of plexuses in human foetus 115 I am glad to acknowledge the award of a Leverhulme Associateship of the Royal Society of Medicine whilst this work was in progress.

REFERENCES ABDULLAH, S. (1958). Studies on the anatomy of the human brachial plexus with special reference to its blood supply. M.Sc. Thesis, University of London. ADACHI, B. (1928). Das Arteriensystem der Japaner. Kyoto: Kenkyasha. BARTHOLDY, K. (1897). Die Arterien der Nerven. Morphol. Arb. Jena, 7, 393458. BERGMANN, L. & ALEXANDER, L. (1941). Vascular supply of spinal ganglia. Arch. Neurol. Psychiat., 46, 761-782. BLUNT, M. J. (1956). Studies on the blood supply of nerve. Ph.D. Thesis, University of London. BOWDEN, R. E. M. (1961). Personal communication. BOWDEN, R. E. M. & GUTmANN, E. (1949). The fate of voluntary muscle after vascular injury in man. J. Bone Jt. Surg. 31B, 856-868. BREIG, A. (1960). Biomechanics of the Central Nervous System. Stockholm: Almqvist and Wiksell. CAVE, A. J. E., GRIFFITHS, J. D. & WHITELEY, M. M. (1955). Osteoarthritis deformans of the Luschka joints. Lancet. 1, 176-179. DENNY-BROWN, D., ADAMS, R. D., BRENNER, C. & DOHERTY, M. M. (1945). Pathology of injury to nerve induced by cold. J. Neuropath. 4, 805-328. GILLILAN, L. A. (1958). The arterial blood supply of the human spinal cord. J. Comp. Neurol. 110, 75-103. HALLER, A. VON (1756). Icones anatomicae. Fasc. I-VIII. Gottingen: A. Vanderhoeck. HOVELAcQUE, A. (1927). Anatomie des Nerfs Craniens et Rachidiens et du Grand Sympathique chez l'Homme. Paris: Doin. MACCONAILL, M. A. (1961). Personal communication. MACCONAILL, M. A. & GURR, E. (1960). The FALG interactions in histology. Irish J. med. Sci. pp. 182-186. MIXTER, W. J. & BARR, J. S. (1934). Rupture of the intervertebral disc with involvement of the spinal cord. New Engl. J. Med. 211, 210-215. POIRIER, P. & CHARPY, A. (1912). Traits d'Anatomie Humaine, 3rd ed. Paris: Masson et Cie. PuTrrY, V. (1927). New conceptions in the pathogenesis of sciatic pain. Lancet, 2, 53-60. QUAIN, R. (1844). The Anatomy of the Arteries of the Human Body. London: Taylor and Walton. QUAIN, J. (1897). Quain's Elements of Anatomy, 10th ed. New York and Bombay: Longmans, Green and Co. RICHARDS,. R. L. (1954). Peripheral nerve injuries: neurovascular lesions. Ed. H. J. Seddon. Spec. Rep. Ser. med. Res. Coun. No. 282. London: H.M.S.O. ROBERTS, J. T. (1948). The effect of occlusive arterial diseases on the blood supply of nerves. Amer. Heart J. 35, 369-892. SAPPEY, PH. C. (1877). Traitd d'Anatomie Descriptive. Paris: V. Adrien Delahaye et Cie. SOULIE, A. (1912). (Poirier and Charpy) Traitj d'Anatomie Humaine. Paris: Masson et Cie. TESTUT, L. (1911). Traite6 d'Anatomie Humaine. 6th ed. Paris: Octave Doin et Fils. TONKOFF, W. (1898). Die Arterien der Intervertebralganglion und der Cerebrospinalnerven des Menschen. Int. Mschr. Anat. Physiol. 15, 353, 401. TORR, J. B. D. (1957). The blood supply of the human spinal cord. M.D. Thesis, University of Manchester. TowNE, E. B. & REICHERT, F. L. (1931). Compression of lumbosacral roots of the spinal cord by thickened ligament flava. Ann. Surg. 94, 327-336.

EXPLANATION OF PLATES PLATE 1 The lumbar and sacral region of a 5-month human foetus, injected with rubber latex and India ink, cleared in tetrahydronaphthalene to show the blood supplyofthe nerve roots and ganglia. x 3J. PLATE 2 The lumbar and sacral regions of a full term human foetus, injected with rubber latex and India ink, cleared in tetrahydronaphthalene to show the blood supply of the nerve roots and ganglia. x 2. 8-2 116 M. H. DAY PLATE 3 Fig. 3. Detail of PI. 2 showing the blood supply of the sacral ganglia. x 17. Fig. 4. Detail of PI. 2 showing vertebral, ganglionic and radicular branches at the fourth lumbar segmental level, on the left side. x 10. Fig. 5. Detail of PI. 1 showing the vessels to the left fourth lumbar ganglion. x 12. Fig. 6. The lumbo-sacral region of a full-term foetus, injected and cleared to show the intraneural vessels of the lower lumbar and upper sacral nerves. x 3. Lat. sac., Lateral sacral artery; Ped., pedicle; Pud. & sup. glut., pudendal and superior gluteal arteries.

PLATE 4 Fig. 7. Longitudinal vessels running both proximally (A) and distally (B) from vessels supplying the sacral plexus. Sodium nitroprusside benzidine stain. x 21. Fig. 8. The capillary plexus, surrounding the peripherally placed ganglion cells, receiving an equatorial ganglionic branch (C). Sodium nitroprusside benzidine stain. x 70. Fig. 9. Longitudinal vessels within the sacral plexus giving rise to fine vessels between the nerve bundles (D). Sodium nitroprusside benzidine stain. x 21. Fig. 10. A group of vessels entering the sacral plexus at the point of union of the ventral rami. Sodium nitroprusside benzidine stain. x 21. Fig. 11. Longitudinal vascular channels within nerve roots, showing transverse interconnexions. Sodium nitroprusside benzidine stain. x 21.