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V.—Distribution of the Cells in the Intermedio-Lateral Tract of the , By Alexander Bruce, M.A., M.D., F.R.C.P.E., F.K.S.E., Physician to the Edin- burgh Royal Infirmary. (With One Plate and Twenty-four Figures.)

(Read June 5, 1905 ; MS. received November 16, 1905. Issued separately March 6, 1906.) The term intermedio-lateral tract was introduced in 1859 [Phil. Trans., 1859, p. 445) by LOCKHART CLARKE to designate a tract or column of nerve cells in the spinal cord, which he had previously described in 1851 [Phil. Trans., 1851, ii. p. 613) as occupying that portion of the lateral margin of the which is intermediate between the anterior and posterior cornua. According to CLARKE'S original account, the column in question was very transparent in appearance, and resembled somewhat the substantia gelatinosa of the posterior horn. It was found in the upper part of the , extended upwards through the dorsal region, where it distinctly increased in size, to the lower part of the cervical enlargement. Here it disappeared almost entirely. In the upper cervical region it was again seen, and could be traced upwards into the medulla oblongata, where, in the space immediately behind the , it blended with its fellow of the opposite side. In the more complete account of the tract published in 1859 (p. 446), its component cells are described as in part oval, fusiform, pyriform, or triangular, and as being smaller and more uniform in size than those of the anterior cornua. In the mid-dorsal region, where they are least numerous, they are found only near the lateral margin of the grey matter, with the exception of some cells which lie among the white fibres beyond the margin of the grey substance. In the upper dorsal region the tract is larger, and not only projects further outwards into the lateral column of the white fibres, but also tapers inwards across the grey substance, almost to the front of Clarke's column. In the cervical enlargement it gradually disappears, although it seems to contain, in part at least, a few scattered cells resembling those of the intermedio-lateral tract of the dorsal region. In the upper cervical region, as already stated, it is again seen occupying a lateral horn similar to that found in the dorsal region. It is composed of the same kind of cells, and can be followed up into the medulla, where it is said to give origin to some of the fibres of the vagus and the spinal accessory. WALDEYER, GASKELL, SHERRINGTON, MOTT, and others have drawn attention to the probability that the dorsal vagus nucleus of the medulla belongs to the same system as the intermedio-lateral tract. GASKELL has shown that sympathetic fibres pass out with the second and third sacral roots, and SHERRINGTON, without giving a definite opinion on the subject, has suggested that the cells which appear in the sacral region as a lateral horn probably belong to the intermedio-lateral tract system. TRANS. ROY. SOC. EDIN., VOL. XLV. PART I. (NO. 5). 14 106 DR ALEXANDER BRUCE

As the present paper concerns itself, however, purely with the tract as it is found in the dorsal, lower cervical, and upper lumbar regions, the question raised in the two previous paragraphs as regards its distribution in the upper cervical and lower sacral regions will not be further referred to. The majority of anatomists who have written on the subject since CLARKE'S original papers appeared have regarded the intermedio-lateral tract as being synonymous with the cells of the lateral horn. This view is not exactly in accordance with the definition or the description and figures of CLARKE, an examination of which shows that, as already stated, he was aware that the tract passed beyond the limits of the lateral horn, both backwards along the margin of the grey matter and also inwards towards the column of CLARKE (Phil. Trans., 1859, p. 446, PI. XX. figs. 2 and 4 ; also PL XXI. figs. 3, 5 and 6). WALDEYER, in his work on the Spinal Cord of the Gorilla (Abth. der Kb'nig. Akad. derWissenschaft, Berlin, 1898), has subjected the intermedio-lateral tract to a careful examination, and has done more than any other writer since CLARKE to advance our knowledge and broaden our views with regard to the character and distribution of its cells. He makes it clear that the cells of the tract are not limited to the lateral horn, but that also at the margin of the grey matter near the formatio reticularis there are found cells identical with those in the lateral horn. These are, in his opinion, therefore, component parts of the intermedio-lateral tract. He is further of opinion that the tract does not, as CLARKE thought, disappear in the cervical and lumbar enlargements, but that it is found throughout the whole length of the cord. While he admits that it may disappear as a lateral horn in the cervical enlargement, he maintains that it is continued upwards as the cells of the formatio reticularis. He is further in agreement with KRAUSE in thinking that the lateral horn of the dorsal region is not identical with the lateral projection of the anterior cornua in the cervical and lumbar enlargements, and that the cells of the intermedio-lateral tract are not mere transformations or modifica- tions (SCHWALBE, BRB, OBERSTEINER, QTJAIN) of the cells in the lateral part of the anterior cornua, but are of altogether independent origin and nature. SHERRINGTON (Journ. Physiol., 1892, p. 698), with reference to these conclusions of WALDEYER'S, says : " WALDEYER, in his description of the grouping of the cells in the cord of the gorilla, says that the lateral horn cells are found throughout the cord in all its segments, including those of the cervical and lumbar enlargements. He divides the ganglion cells of the cord into as many as fourteen definite groups, attaching to each a name, but treats the cells of the lateral and those of the lateral horn as one group (Mittelzellen). When he says that the cells of the lateral horn are present in, for instance, the eighth and seventh cervical segments, his meaning is that there are cells in the reticular formation at that level which he considers are cells of the lateral horn, although that horn can no longer with certainty be recognised. But in regions where the lateral horn exists there are cells in the lateral reticular formation as well as in the lateral horn, and the assumption that the cells of the lateral reticular formation, although somewhat similar to the cells of the lateral horn, are identical with ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 107

them, or are their equivalents, is a somewhat insecure foundation on which to rest the statement that the cells of the lateral horn are present in a region where there is no other evidence of them beyond cells in the lateral reticular formation." SHERRINGTON has not been able to trace lateral horn cells higher than the middle of the superficial origin of the eighth cervical nerve. In Rhesus he has not found them above the surface origin of the first thoracic root. The lower extremity of the tract he finds to correspond to the surface origin of the fourth lumbar nerve. This would correspond to the third lumbar segment in man. As regards the longitudinal distribu- tion or grouping of the cells in the intermedio-lateral tract, WALDEYER notes, on p. 19, that they lie close together, and that they may be arranged in groups or clusters separated by interspaces in which there are no cells. " Beziiglich ihrer Anordnung ist zu sagen dass sie gewohnlich dicht zusammengedrangt liegen. Selbst wenn keine grossere Zahl dieser Zellen vorhanden ist liegen sie haufig zu zweien, dreien oder vieren nahe beisammen ; zwischen diesen einzelnen kleinen Gruppen konnen dann allerdings grossere Zwischenraume vorhanden sein. Jedenfalls bilden diese Zellen stets eine besondere Formation im Riickenmarke." This arrangement of the cells in groups or clusters has also been referred to by AINSLIE HOLLIS, in the Journal of Anatomy and Physiology, vol. xvii., 1883, p. 63 : " The (intermedio-lateral) tract consists of clusters of small (mostly pyriform) cells arranged linearly, and dissociated from each other, and from the column of sparsely scattered giant cells to which they are contiguous, by a delicate fibrillar stroma of synectic tissue. In the mid-dorsal region I have observed two adjacent columns of these cell-clusters." Again, at p. 520, referring to " the vesicular columns of CLARKE and the tractus intermedio-lateralis," he says that " in certain parts of the cord they are found closely congregated in cell-nests." MOTT (Brain, 1890, p. 444) says: "The cells of the intermedio-lateral tract are found throughout the dorsal region. The cells are bi-polar, and in vertical sections they are often seen to exist as little groups or nests of vesicular cells, from eight to twelve in number." ONUF and COLLINS (Sympathetic Nervous System, 1900, p. 140), in describing the cells of the lateral horn, say : " The group is represented by a very pure type in the lower dorsal region. In longitudinal sections it does not appear in the form of a continuous column, but segmented, in the form of cell-nests distributed at intervals." ARGTJTINSKY, a pupil of WALDEYER'S, in a valuable paper in vol. xlviii. of the Archiv fur mikroskopische Anatomie (1897), " Ueber eine regelmassige Gliederung in der grauen Substanz des Riickenmarks beim Neugeborenen und iiber die Mittelzellen," in which he for the first time describes a segmentation of the " Mittelzellen" of WALDEYER, refers, on p. 514, to a somewhat similar mode of grouping of the cells of the intermedio-lateral tract. He says: " Verfolgt man die Seitenhornzellsaule in einer Serie von Sagittallangsschnitten, vom Seitenstrang zur Mittellinie vorschreitend, so sieht man, wenn man dem Seitenhorn sich nahert, erst eine oder ein paar Langsreiheu 108 DR ALEXANDER BRUCE von einzelnen Zellen, wie Perlschniire, zwischen den Langsfasern des Seitenstrangs angeordnet. Dann werden diese einzelligen Eeihen zahlreicher. . . . Die einzelnen Glieder der Seitenhornzellsaulen sind zwar grosser, als die Mittelzellengruppen, doch sind die Abstande zwischen den Centren zweier Gruppen sowohl bei den Seitenhornzellen, wie den Mittelzellen gleich so dass beide Zellsaulen Ketten bilden, welche gleich viele und gleiche gelagerte Glieder besitzen." A first perusal of this paper might leave the impression that the segmentation of the middle cells had been confounded with that of the posterior part of the intermedio-lateral tract, but ARGUTINSKY has stated, in a most categorical manner, that the two systems of cells are distinct in form and in position, although he admits that they may approach each other very nearly. An examination of the text of WALDEYER'S paper and his plates and diagrams of sections from man and the gorilla shows also that the " Mittelzellen " and the intermedio-lateral tract are two independent systems. WALDEYER has personally confirmed this statement, after examining my preparations. It is evident, therefore, that ARGUTINSKY has noted a segmental grouping of the cells of the intermedio-lateral tract. HERRING (Journ. Physiol., 1903, p, 285) says : "The cells of the lateral horn vary in size considerably. They occur in groups, and in some sections may be absent from the lateral horn altogether." The above references and quotations indicate that several observers had noted the fact that the intermedio-lateral tract is not a continuous column of cells, but that its cells are arranged more or less in groups. So far as I am aware, however, no exhaustive examination has up to the present time been made of the distribution of the cells in the tract. This want it is the object of the present communication to supply. In 1903, while engaged in the study, by means of serial sections, of the distribution of the large motor cells and of the smaller and more faintly staining polygonal cells in the cervical enlargement of the spinal cord, I was struck with the appearance in the first dorsal segment, and to a lesser extent in the lower part of the eighth cervical segment, of special groups of cells differing in character and in arrangement from the above-mentioned large motor and small polygonal cells. These groups were situated within or adjacent to the posterior border of the lateral portion of the anterior horn. Under a low power of the microscope they readily attracted the eye, owing to the facts that they were closely grouped together, that they were fusiform in outline, and that their long axes for the most part ran in the same direction. These features, and the fact that they stained almost as deeply as the large motor cells, rendered them exceedingly conspicuous. In the eighth cervical and in the upper part of the first dorsal segments they were found entirely in the either at a little distance from or quite close to the anterior cornu. In either case they lay behind the junction of the outer and the middle thirds of its posterior border, or behind the outer third. In the lower part of the first dorsal segment this position was departed from, and they gradually encroached forwards upon the grey matter and at the same time passed outwards towards the lateral margin of the anterior cornu. To speak more accurately, this relative change ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 109 of position was due to the recession and shrinkage of the anterior cornu, owing to the diminution in the number of its large motor cells which takes place here. Another feature which characterised these cells—a feature which led to this special investigation —was this, viz., that they were not found in each of the successive serial sections. It was noted that they would suddenly appear as a small group of two or three cells, and that in succeeding sections they rapidly rose to a maximum. They then almost as rapidly diminished in number, and thereafter disappeared entirely from the field throughout a varying number of sections. This phenomenon repeated itself eight or nine times in the first dorsal segment. As the lower end of this segment was approached, the groups became larger and the intervals between them shorter. On tracing the groups downwards into the lower part of the first and through the second dorsal segment, it was evident that the cells forming them were the same as those which are there recognised as the intermedio-lateral tract. The examination of the eighth cervical and first dorsal segments of a second, and of corresponding segments of a third cord demonstrated that this arrangement of the cells in groups separated from each other by distinct intervals was a constant phenomenon, and not an individual peculiarity of the cord first examined. The question then presented itself—Was this arrangement of the cells in groups limited to the two segments in question (C. 8 and D. 1), or did it extend throughout the whole of the length of the intermedio-lateral tract, and if so, was there, as had been established in the case of the motor cells in the cervical and lumbo-sacral regions, any grouping of the cells which might be regarded as charac- teristic of each segment in which it was found ? In order to determine these points the third cord was examined from the upper part of the cervical enlargement to its lower extremity. This cord, obtained from an individual presumably free from any disease of the nervous system, was hardened in formalin and divided into root segments accord- ing to the manner employed in preparing the sections for my " Topographical Atlas of the Spinal Cord," sections as nearly as possible at right angles to the median plane of the cord being made below the lowest fibres of each nerve root. The segments so obtained were further hardened in alcohol, embedded in celloidin, and divided into serial sections of uniform thickness. The sections were stained with toluidin blue or with Unna's polychrome blue, with FORD ROBERTSON'S precautions to prevent decolorisation.* Special means were taken to ensure that the corresponding sides of each section had a corresponding position on the slide, so that on this ground there should be no error in the enumeration of the cells on either side, or in comparison of those of one side with those of the other. Some 7000 sections in all were examined. Of these more than 5000 contained cells of the intermedio-lateral tract. These cells, as found on both sides of the cord, were carefully counted independently by four different observers, f The

* This group of stains is specially suitable, as it singles out the nerve cells and throws them into such relief that they are more easily enumerated than if stained by any other method. t I take this opportunity of acknowledging my indebtedness to Dr MACFIB CAMPBELL, Carnegie Research Scholar, for assistance in preparing the sections and enumerating the cells ; to Dr HARVEY PIRIE, B.SC, for assistance in enumerating cells ; and to my son, A. NIUIAX BRUCE, for making the drawings for the figures 1-24. 110 DR ALEXANDER BRUCE

results arrived at were then compared, and any discrepancies were considered and cor- rected. In this way greater precision as to the lateral boundaries of the tract and the number of its cells was arrived at than would have been possible for a single observer. The results of the finally corrected enumeration were then plotted graphically on the diagram (PI. I.). I am satisfied that the numbers are in no case excessive.* In C. 8 and D. 1, and in D. 2 (upper part), the enumeration of the cells of the inter- medio-lateral tract presented no particular difficulty. They formed very compact and sharply circumscribed clusters, and their form and arrangement were so different from those of any of the motor cells of the anterior cornu which were adjacent to them that there was not the slightest difficulty in distinguishing the one from the other. This was true in C. 8 and upper D. 1, where the cells lay behind the lateral part of the anterior cornu, and in lower D. 1 and .upper D. 2, where they formed a group limited to the apex of the lateral horn proper. In the enumeration of the cells which lay between the lower part of D. 2 and the lower extremity of the tract, two difficulties were met with—one from the frequent absence of definition of the inner margin and the other from the want of precise information as to the posterior limit of the tract. On the inner aspect of the tract there were frequently seen small polygonal cells, sometimes in fairly compact groups, sometimes as more scattered cells. These, which evidently corresponded to the " Mittelzellen" of WALDEYER, sometimes approached very closely to the cells of the intermedio-lateral tract, but with care they could generally be separated from the latter. After a short training in the enumeration of the cells, there was generally a close agreement between the various observers as to the limits of the intermedio-lateral tract and the Mittelzellen. There seemed little doubt that the Mittelzellen did not represent a part of the intermedio-lateral tract. The second difficulty, that of determining the posterior limit, was a much more serious one. It arose from the fact that groups of cells of a character practically identical with that of those found at the tip of the lateral horn were situated at the margin of the grey matter, either underlying or partially entering into the formatio reticularis, and extending as far back as the level of the posterior margin of Clarke's column, or e^en further. In certain sections this series of cells (which will be referred to in future as the reticular cells, from their relation to the formatio reticularis) seemed absolutely distinct and separate from that situated at the apex of the lateral horn (the apical cells). In consecutive sections it was found that the interval between the two sets of cells lessened gradually until they came to approach each other closely, and even to fuse so completely that it became impossible to distinguish the one from the other. It was also observed that, almost without exception, the number of the apical cells and that of the reticular cells rose and fell together; when the one reached its maximum so did the other, and vice versa. At first I was inclined (Rev. Neurol. and * At the upper and lower limits of each segment one or more sections were generally lost, owing to causes which could hardly be avoided. In D. 11 some fifty sections were rendered useless owing to an accident from a fire which occurred in the laboratory when the work was in progress. With these exceptions the sections were practically continuous. ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIOLATERAL TRACT. Ill

Psychiat., vol. ii. p. 582) to regard the reticular series of cells as distinct from the apical one, and consequently endeavoured to enumerate them independently of each other. This was, in those sections where the two sets of cells were not in contact, a simple matter; but in a great many sections it was quite impossible to trace any line of demarcation between the two, so closely were they fused. On making a second enumeration so as to include the reticular cells along with those at the apex of the lateral horn, the remarkable fact became evident that the effect on the groups plotted out in the chart was simply this, that the maxima were increased jand the minima remained unaltered. A. further careful examination of the relation of the two rows of cells throughout the dorsal region and the first lumbar segment showed that in following them through a series of sections it was always possible to trace them into intimate connection with each other. The posterior or reticular cells were therefore included in and enumerated as an integral part of the intermedio-lateral tract. This opinion was not arrived at without full consideration, and it was satisfactory to find on a subsequent study of WALDEYER'S work on the spinal cord of the gorilla that it had the support of his authority. The results of the examination of each segment may now be stated. Eighth Cervical Segment.—This was divided into 280 sections. Its intermedio- lateral tract contains 429 cells on the right and 595 on the left side. These are distributed as follows (see graph): The upper fourth part of the segment is practically devoid of cells, there being only one cell on the right side (situated in section 68), and on the left side one each in sections 67 and 69. The second fourth contains three small groups of cells, separated by wide intervals. The number of cells seen in any one section never exceeds four, and the number in the largest group (R. 108-119) is thirty-one. The third fourth contains on the right side three small groups. If the cells on the left side of sections 144-162 inclusive be regarded as belonging to one group, and those from section 173 to 187 as comprising another, there are two small groups and the beginning of a third on the left side. The lowest fourth contains by far the largest number of cells in the segment. In the right side these are distributed in four and on the left in three groups. The largest of these is on the left side. It extends from section 192 to 227, and contains 286 cells. The preponderance of the cells on the left over those on the right is due mainly to this nucleus. Throughout the whole segment the cells of the intermedio-lateral tract are situated in the white matter. They are all " outlying," as SHERRINGTON has termed them, although they vary somewhat in their distance from the grey matter. They are connected with this, however, by strands of connective tissue. Their long axes corre- spond to the direction of these strands, and for the most part run parallel to the adjacent border of the grey matter, being thus oblique outwards from behind forwards. No reticular group is seen. Such cells as are situated behind Clarke's column and 112 DR ALEXANDER BRUCE

the formatio reticularis are of the small polygonal type characteristic of the " Mittel- zellen " of WALDEYER. Note.—It may be stated here that no cells which could be definitely considered to belong either to the apical or to the reticular portions of the intermedio-lateral tract were found in any segment of the cervical enlargement above the limit indicated in C. 8. Any group of cells that was seen in the grey matter between the anterior and posterior cornua and internal to the formatio reticularis belonged evidently to the " Mittelzellen," and not to the intermedio-lateral tract. First Dorsal Segment.—This was divided into 202 sections. Its intermedio- lateral tract contains 1720 cells on the right and 1837 on the left side. These are distributed in sharply defined groups, with distinct, and, as a rule, wide intervals between

c.c.

FIG. 1 (C. 8, 247, L.).—Two groups of cells belonging to the intermedio-lateral tract are seen. Both are outside the grey matter of the lateral part of the anterior cornu. The larger of the two is a group of closely aggregated cells, close to the margin of the horn, and having their long axes pointing outwards and somewhat forwards. In the smaller group, which is further removed from the horn, the cells are more irregularly placed, but their long axes on the whole point outwards. them (see graph, D. l). As in C. 8, the largest cell-groups are situated at the lower extremity of the segment. With one exception (the fourth on the left) the groups resemble each other in that the number of their cells rapidly rises to a maximum and then almost equally rapidly falls away to zero. The graph thus presents the appear- ance of a succession of spires. Of these there are ten (or possibly only nine) on the right and eight on the left side. While there is a close resemblance of form between [The figures in the text represent transverse sections of certain of the cells from the various segments examined. The position in the segment is indicated thus : C. 8, 247 means the two hundred and forty-seventh section of the eighth cervical segment. R. and L. indicate right and left sides respectively. a. m. Anterior median group of motor cells. a. I. Antero-lateral „ „ p. I. Postero-lateral „ „ p. p. I. Post-postero-lateral „ „ c. C. Clarke's vesicular column of cells. i. I. t. Intermedio-lateral tract. m. c. The middle cells of anterior cornua : the Mittelzellen of WALDEYER.] ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 113 the cell-groups on the two sides, this resemblance does not amount to a perfect symmetry. The largest group (the lowest on the right side) contains 578 cells, and the largest number of cells in any one section is 58. At the upper extremity of the segment the intermedio-lateral tract is distributed on the posterior border of the anterior cornu, a little internal to its lateral tip ; but, with the progressive diminution of the number of large motor cells, its position relative to these continues to shift outwards until, near the lower end of the segment, it comes to lie at the apex of what is now the lateral horn proper. The cells in the upper part of the segment lie for the most part within the grey matter, quite close to its margin, but wherever their number undergoes a considerable increase they tend to project outwards

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FIG. 2 (D. 1, 175, R.).—The cells of the intermedio-lateral tract form a large group, partly within and partly without the cornu, a few being separated by a distinct interval from the main group. The majority of the cells have their long axes in an oblique direction, and more or less parallel to the posterior margin of the horn. into the white matter. In some groups the cells are, on the other hand, almost entirely " outlying," or there may be a few outlying cells, while the main mass of the cells is found in the grey matter. In the upper part of the segment the cells are closely aggregated ; but at its lower part, where the lateral horn proper is fully con- stituted, they are less compactly grouped, and tend to spread along the posterior, and, even in some places, also along the anterior border of the horn. This anterior group sometimes becomes separated off from the cells at the tip of the horn. Those on the posterior margin spread further from the apex than the anterior ones, but they do not reach the formatio reticularis. There is no indication of any reticular group in this segment. The long axes of the cells are in general parallel to the margin of the grey matter, although the outlying cells assume the direction of the strands of connective tissue in which they lie. TRANS. ROY. SOC. EDIN., VOL. XLV. PART I. (NO. 5). 15 114 DR ALEXANDER BRUCE

Second Dorsal Segment.—This segment contained 228 sections. The cells of its intermedio-lateral tract number 3635 on the right and 3931 on the left side. The groups of cells, as represented in the graph, retain their spire-like appearance, the rise and fall of the cells in each group being still rapid. The spires are more slender on the right side. The intervals separating them are shorter than in D. 1, and not always complete. The groups are wider here than in D. 1, each one being spread over a larger number of sections, especially on the left side. They number 12 to 15 on the right, and 11 or 12 on the left. As in D. 1, though there is a general resemblance of form on the two sides, the symmetry is not quite complete. The largest number of cells in any one section is 58.

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FIG. 3 (D. 2, 4, R.).—The cells of the intermedio-lateral tract are FIG. 4 (D. 2, 169, L.).—This figure is taken from a now at the apex of the lateral horn proper. The long axes of section through that portion of the tract in which the cells have no constant direction, and the cells are not so the reticular cells first appear. Their position at the closely compacted as in the previous figure. A small aberrant re-entrant angle of the grey matter and their partial group of post-postero-lateral cells (p. p. I.) is seen near the separation by a slight interval from the apical cells re-entrant angle between the lateral and the posterior cornua.

As regards their distribution, the cells sometimes form a triangular group, the apex of which occupies the tip of the lateral horn ; sometimes they stretch as a band along the posterior margin of the lateral horn. There are a few outlying cells in the white matter (fig. 3). In the lower half of the segment, at section 165 on the left side, we have the first definite appearance of the reticular group (fig. 4). At its commencement, which is abrupt, it is apparently a separate group, but two sections below that at which it is first observed it becomes continuous with the original group of intermedio-lateral cells, and is hardly distinguishable from it in so far as size of cells is concerned. This reticular group dies out again in section 174 on the left side. On the right side (fig. 5) it appears first in section 177, then gradually increases in size, spreads back along ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 115 the posterior border as far as the posterior limit of Clarke's column, and disappears in section 186. It reappears as a small group on both sides in section 199, and again on the right from section 204 to section 216. As regards the position of the cells, when these lie at the apex of the horn in a triangular group, their long axes show no constant direction, but when they extend in bands along the posterior margin, their long axes run parellel to the border (figs. 3 and 4). In the upper part of this segment a few aberrant cells of the post-postero-lateral group are found among and internal to the cells of the intermedio-lateral tract (fig. 3). A fact which is worthy of note as regards this segment is the remarkable vascularity

FIG. 5 (D. 2, 181, R.).—This is drawn from one of the sections which show the first appearance of the reticular cells on the right side. The cells underlying the formatio reticularis are few in mnnher, but there is a large group at the base of the lateral horn, and separated from the apical cells by a slight interval. of the intermedio-lateral tract, vessels passing into it directly from the lateral periphery of the cord. Third Dorsal Segment.—This segment was divided into 276 sections, in which the cells of its intermedio-lateral tract number 7471 on the right side and 7297 on the left. The graph of this segment presents a remarkable contrast to those of D. 2 and D. 4, in both of which the groups of cells are represented as slender spires, separated from each other by distinct intervals which are almost devoid of cells. In D. 3, on the other hand, with one or two exceptions about the centre of the right side, the groups of cells are arranged in broader masses, with less indication of a spire-like arrangement. The masses are separated by less distinct intervals, in which there always remain a considerable number of cells. The intervals are so indistinct that it is difficult to be certain of the number of groups on the right side. Probably there are fifteen. On the left side there appear to be thirteen groups, and there may have been fourteen, as some sections at the lower end of the segment (owing to an accident in preparation) do not show the grey matter on the left side. This great increment of the cells is due to the 116 DR ALEXANDER BRUCE

large number both in the apical and in the reticular groups. The reticular group is generally present at the re-entering angle between the anterior and the posterior cornua. It is either continuous with the apical group or separated from it by a distinct interval. Its cells are sometimes arranged in a triangle with its apex inwards, and its base towards the formatio reticularis. Its cells lie generally with their long axis pointing forwards and inwards. The apical group either lies at the tip of the lateral horn or forms a triangle of considerable size, with its base inwards, and there is a tendency for the cells to extend along the anterior surface of the lateral horn as a special anterior group (D. 3, 74 ; fig. 6). No distinct difference in the size of the cells contained in the apical and reticular groups could be made out.

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Fie. 6 (D. 3, 74, L.).—This figure shows a large anterior group of cells in the intermedio-lateral tract, the apical cells being few and the reticular ones being unrepresented.

Fourth Dorsal Segment.—This segment was divided into 182 sections, and its intermedio-lateral tract contains 3803 cells on the right side and 3623 on the left. The groups of cells, as represented on the graph, show a return to the spire-like arrangement of D. 2, with this difference, that the spires as a rule are higher than and not quite so slender as in D. 2. The intervals between them are, however, very distinct. There are nine groups on the left and ten on the right side. (An eleventh group at the lower end of the segment is continued into the first group of D. 5, and is therefore not enumerated here.) The greatest number of cells in any one section (149 on the left side) is 82. This is the greatest number found in any one section of the whole intermedio-lateral tract. In this group there is, in fifteen sections, a rise from 5 cells to 82, and then a fall again to 2 cells. In section 149 (fig. 7) the connection and identity of the apical and reticular groups is clearly established. On examining the sections in which this group was found, it is easy to see that where an interval appears between the two sets of cells it is caused merely by the presence of a bundle of nerve fibres, and is not due to any real difference in the nature of these cells. There is no constant difference in the size of the cells in the ON DISTRIBUTION OF THE CELLS IN THE LNTERMEDIO-LATERAL TRACT. 117

two cell-systems, there being a greater disparity in the size of the cells contained in either group than between those of the two individual groups. This association of the two groups, reticular and apical, as will be seen, could be traced throughout all the lower parts of the region in which the two tracts were found. The reticular group occasionally curves inwards in front of Clarke's column (fig. 8, D. 4, 151). The apical sometimes gives off a small anterior group on the anterior aspect of the lateral

CL.m .

Fie. 7 (D. 4, 149, L.).—In this section the apical and FIG. 8 (D. 4, 151, L.).—This figure shows the continuity of reticular cells form one long continuous group, which the apical and the reticular cells, and also a tendency extends from a point in front of the tip of the lateral of the group to extend inwards in front of Clarke's horn to a point much behind the level of Clarke's column. column. Eighty-two cells were counted in this section. A few of them were situated in the white matter. horn. There are a few outlying cells near the tip of the lateral horn, but a greater number in the formatio reticularis. Fifth Dorsal Segment.—This segment was divided into 350 sections, in which the cells of the intermedio-lateral tract on the right side amount to 7407 and on the left to 7958. The segment shows a remarkable difference between its upper third and its lower two-thirds. In the upper third the groups as represented on the graph continue to show a spire-like character, closely resembling that of D. 4, although of a less slender type, and on the whole with less complete intervals. In the lower two- thirds the spire-like character is less marked. There is a remarkable change in the character of the groups, there being a gradual transition towards the types of D. 6 and D. 7, in which the graph suggests mounds with rounded tops on which are superposed short and slender spires. The intervals between the groups in the lower two-thirds are distinctly less than in the upper third. The number of the 118 DR ALEXANDER BRUCE

groups on the right side is difficult to determine ; probably there are fourteen. On the left side there are fourteen fairly distinct groups. This transition in the character of the graph is associated with a decrease in the number of cells in the apical and a rise in that of the reticular series. The latter tends in the lower two-thirds of the segment to assume a distinct wedge-shape, with its apex pointing inwards and forwards in front of Clarke's column (fig. 9, D. 5, 238). In some parts the cells of the reticular group appear slightly smaller in size than those of the apical group, but this relationship is not constant. The outlying cells are rather numerous, especially near the tip of the

e.c

FIG. 9 (D. 5, 238, R.).—The reticular cells form a large group, of a wedge-shape, with its apex pointing inwards in front of Clarke's column and its base situated on the formatio reticularis. The apical cells are here relatively few in number. lateral horn. The oscillations in the number of cells are greater in the reticular than in the apical group. Sixth Dorsal Segment.—This segment was divided into 438 sections, the inter- medio-lateral tract consisting on the right of 8030 and on the left of 8105 cells. Fifteen groups were counted in each side. The graphic chart of these shows that the change begun in D. 5 is continued throughout the segment, the lower half bearing a close resemblance to the appearance found in D. 7. There are no high ascents, and no complete intervals between the mound-like elevations. In section 152 on the left side 58 cells were counted—the maximum number in the segment. In most of the other sections the maximum number lay between 30 and 40. In this segment is the only instance of an exception to the rule that the numbers of the apical and reticular groups rise and fall simultaneously. In a cluster which lies between sections 270 and 340 the apical group reaches its maximum while the reticular group is at its minimum. Throughout the segment the reticular group as a whole is considerably smaller than it is in D. 5. Its cells are more loosely scattered, with less of a triangular arrangement, ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 119

and are more separated by bundles of white fibres than in D. 5 (fig. 10, D. 6, 253 R.). The cells in the apical group are frequently of a large size, measuring 40-50 M- The vascularity of the group is very remarkable, and it is noticed that the main supply comes from the vessels of the periphery of the cord. Seventh Dorsal Segment.—This segment was divided into 518 sections. The intermedio-lateral tract on the right side contains 8282 and on the left 8739 cells. Sixteen groups can be counted on each side, and they present a very uniform character throughout the segment. They are rather more distinctly demarcated on the right than on the left side. They present the mound-like appearance found in the lower half of D. 6, with rounded tops, but with less tendency on the whole to the formation of small superposed spires. The maximum number of cells is generally between 30 and

C.C.

FIG. 10 (D. 6, 253, R.).—The reticular cells are widely scattered, are fewer in number, and have no triangular outline. The apical group contains cells of large size. 40, and the minimum usually under 10. The largest number of cells in this segment is 43 (in section 368 on the right side). There are no complete intervals between the groups. Although the graphs are fairly similar on the two sides, there is a marked difference in the form of their lateral horns. On the right side, in the lower part of the segment, the lateral horn remains as a distinct spike, whereas on the left side it is almost entirely absent, being limited to a slight rounded prominence (fig. 11, D. 7, 151). The reticular group forms a less distinct feature than the apical one. It is difficult to delimit, especially on the inner side. It is either continuous with or separated from the apical group. The apical group is either fairly compact or its cells are more widely scattered. In both groups the cells are relatively large, presenting frequently a close resemblance in size to the motor cells of the anterior cornua (fig. 12, D. 7, 316). Their exact measurements are 40 M to 60 /*. Eighth Dorsal Segment.—This segment was divided into 430 sections. The inter- medio-lateral tract contains on the right 5943 cells and on the left side 6223. The graph is, on the whole, similar to that of D. 7. The groups are somewhat more definitely 120 DR ALEXANDER BRUCE

marked off from each other, but there is less difference between the maxima and the minima. The average maximum number of cells is the lowest in the whole of the intermedio-lateral tract, amounting generally to between 20 and 30 cells, the highest recorded being 41. The minima are generally under 10. The groups are more distinct on the right than on the left side, and there are 11 on the right and 13 or 14 on the left (see graph). The lateral horn has only a slight indication of a pointed apex. When this is present it is generally on a level with Clarke's column. The reticular group is similar to that found in D. 7, as its cells are scattered and badly marked off from those on its inner aspect. It frequently extends backwards behind Clarke's column (fig. 13 and fig. 14, D. 8, 112 and 370), and it contains a considerable number of outlying cells in the formatio reticularis. There are a few outlying cells in the neighbourhood of the apical group (fig. 13, D. 8, 112). The cells vary in size.

U.i

FIG. 11 (D. 7, 137, L.).—The reticular and apical cells are Fie. 12 (D. 7, 316, L.).—The lateral horn is now a mere loosely aggregated, not sharply bounded on the inner rounded prominence. There are large cells in apical and side. The lateral horn is less prominent than at higher reticular groups ; these are shown in the anterior part of levels. the apical group, and one in the reticular group.

Some very large multi-polar cells are found -in the apical group, and there is a tendency to an admixture of small rounded with medium-sized cells in the reticular group. As in D. 7, the vascularity of the apical group is remarkable, and the supply appears to come mainly direct from the lateral periphery of the cord. Ninth Dorsal Segment.—This segment was divided into 568 sections. The intermedio-lateral tract on the right side consists of 8987 and on the left of 9011 cells. The graph is similar to that of D. 8, except in the lower third, where there is a slight tendency on the right side to the reappearance of a spire-like arrangement. The cell clusters are somewhat less distinct from each other than in D. 8, the minimum number of cells in the intervals between them seldom falling below 10. The average maximum number of cells in the clusters is about 40, the largest number being 56 on the right side. On the left side the average maximum is about 30, and the largest number is 41. There are 18 clusters on the right side, and on the left either 18 or 20. ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 121

a.rn.

C.C.

C-C.

FIG. 13 (D. 8, 112, R.).—The reticular group of cells ex- FIG. 14 (D. 8, 370, L.).—The apex of the lateral horn is at a tends backwards behind Clarke's column. It is in- level posterior to the central canal. The reticular cells definitely bounded on its inner side. The apical group lie almost entirely behind the level of the column of is small and shows several distinct outlying cells. Clarke. The reticular and apical groups are almost con- tinuous, and they are indefinitely bounded on their inner side. The reticular cells form a sort of wedge which points towards the front of the column of Clarke.

tft.Al .

Ut e.c

FIG. 15 (D. 9, 168; L.).—The lateral horn with its bluntly FIG. 16 (D. 9, 413, R.).—The lateral horn shows a sharp apex, pointed apex lies behind the equator of Clarke's column. directed backwards and outwards, and lying at the level The altered shape of the horn, with its reticular group of the posterior half of the column of Clarke. The apical lying internal to rather than posterior to the apical group is distinct and is continuous with the reticular group, is shown. The two groups are continuous, and group. there are several outlying cells near the apical group.

TRANS. ROY. SOC. EDIN., VOL. XLV. PART I. (NO. 5). 16 122 DR ALEXANDER BRUCE

The lateral horns of the two sides continue to present a marked want of symmetry. In the upper part of the segment on both sides the horn presents a blunted or rounded tip, and the apical group lies either at or behind this. On both sides the apex of the lateral horn lies on a plane which passes through the posterior part of Clarke's column (fig. 15, D. 9, 168). On the right side in the lower part a projecting lateral spike appears, and this contains the apical group (fig. 16, D. 9, 413). On the left side the lateral horn has no sharp point, but simply a slightly bulging outline. The cells of the intermedio- lateral tract lie along the outer side of the grey matter, and they extend as far back as the outer side of Clarke's column. The reticular group lies internal to rather than behind the apical group at the upper part of the segment, and on the left side it is simply a backward continuation of the apical group along the outside of the grey matter without any delimitation from it. The cells are not of uniform size in either group, and very large cells from 40 M to 60 M are occasionally found scattered through the apical group. The vascularity of the tract, as in D 8, is still very pronounced. Tenth Dorsal Segment.—The segment was divided into 511 sections. The intermedio-lateral tract contains on the right 10,203 and on the left 8903 cells. The number of cells on the right side thus exceeds that on the left by 1300. This remark- able difference is greater than that found in any other segment. It is one, moreover, which is not attributable to any accidental cause. The cell groups, as represented on the graph, are rounded on the top, and they tend to increase in size in the lower two- thirds of the segment. They are badly marked off from each other, the minima being rarely under 10. The average maximum on the right is about 40, that on the left about 30, the greatest maxima on the left being 46, and on the right 44. As regards the form of the lateral horn there is asymmetry as great as that in D. 9. The left side has practically no lateral spike, but merely a slight rounded bulging of the grey matter. The apical group is placed either at the most prominent part of the swelling, or, more commonly, a little behind it. On the right side in the upper part there is a slight lateral spike in which the apical group is situated, but throughout the greater part of the segment the lateral horn forms a rounded projection similar to that found in the left side (fig. 17, D. 10, 208). On both sides the apical group may be compact or scattered ; most commonly it is spread out along the edge of the grey matter (fig. 18, D. 10,225). The reticular group lies behind the apical, and is either continuous with it or separate from it. The boundaries of the whole tract, more especially those of the reticular group, are rather indistinct, especially when the cells are few and scattered, many of these cells being small and little different from the middle-cells and the small cells in the neighbourhood of Clarke's column. As showing the indefiniteness of the boundaries, the enumerations of the different observers presented greater variations in this than in any other segment. The cells, especially in the reticular group, are small. Outlying cells are not common. Eleventh Dorsal Segment.—This segment was divided into 413 sections. The intermedio-lateral tract on the right side contains 6498 and on the left 6261 cells. ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 123

This number is considerably less than the real number, because 24 sections were entirely lost owing to the accident already referred to. In so far as the graph is continuous, the upper end of the segment is similar to that of D. 10. The lower two-thirds show a marked return to a spire-like arrangement and to an increase in the size of the groups, the maxima being generally very high, reaching in section 312 to 55 on the right and in section 302 to 45 on the left side. The groups are more sharply separated than in D. 10, but they cannot be enumerated owing to the loss of sections. In this segment the reticular group assumes an increasing importance, although it

tit

e.c c e. Lit.

L Lt

FIG. 17 (D. 10, 208, R.).—The rounded projection of the lateral FIG. 18 (D. 10, 225, L.).—As on the right side, the horn and its position at a level corresponding to the posterior rounded form of the lateral horn, and its recession part of the column of Clarke are shown. The apical and to a plane much behind that of the central canal, reticular groups form an almost continuous row of cells at are shown. The scattered cells and indefinite the margin of the grey matter. The inner boundary of the boundary of both apical and reticular groups of cells group is very indefinite. There are also a few outlying cells. which are continuous are also seen. does not yet exceed the apical group in numbers. Near its lower end as many as 22 cells were counted in individual sections. The group possesses the same character and relative position as in D. 10, but its limits are somewhat more easily determined. There are no complete intervals between the apical groups. The apical cells are arranged somewhat similarly to those in D. 10, with the occasional occurrence of a small separate anterior group. The lateral horn is rounded as in D. 10 in the upper part (fig. 19, D. 181, L.), but at the lower end the spike reappears on the right side (fig. 20, D. 11, 312). Twelfth Dorsal Segment.—This segment was divided into 405 sections. The inter- medio-lateral tract contains 8545 cells on the right side and 7888 on the left. The 124 DR ALEXANDER BRUCE graphic representation of the groups shows a return to broad spires somewhat similar to those of D. 3. There are 13 groups on the right and 15 on the left. The greatest number of cells in any one section is 62 (in section 232 on the right side). While the apical group still remains the larger, the reticular has now a maximum number of 35 cells. As in D. 11, the reticular cells are arranged in nests with complete intervals in which there are no cells. These intervals are, however, shorter than in D. 11, so that the reticular group has a relatively greater value in this segment. The apical group is situated partly at the spike-like tip of the lateral horn and along the posterior border,

FIG. 19 (D. 11, 181, L.).— The lateral horn forms merely a FIG. 20 (D. 11, 312, R.).—The lateral horn has a prominent slight rounded elevation without any definite pointed tip, directed slightly backwards, and lying at a level tip. The cells of the intermedio-lateral tract are distri- behind the central canal. Apical and reticular groups buted along the margin. The most posterior of them are both particularly well-developed. The lateral ex- pass as far back as the hinder limit of Clarke's column. tends further back than the hinder limit of Clarke's Internally they have no definite boundary. The apical column. and reticular groups are here quite inseparable. and occasionally has outlying cells amongst the fibres in the neighbourhood of the tip. The reticular group is found either round the re-entering angle and continuous with the apical group, or (fig. 21) it forms a separate group extending somewhat inwards towards the central canal (fig. 22). The two groups show no characteristic difference in the cells, although many of them appear in both groups to be of comparatively large size. The lateral horn is not pointed in the upper half of the left side (fig. 21). On the right and in the lower half of the left it is pointed, and increases in size towards the lower end (fig. 22). First Lumbar Segment.—This was divided into 352 sections. The intermedio-lateral tract contains 7655 cells on the right side and 7053 on the left. The groups in this segment present in the graph an arrangement into lofty and for the most part slender ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 125 spires. There are 19 groups ou the right and 18 on the left side. The maximum number of cells in any single section is 78 (section 29 on the left side; fig. 23). The reticular group is increasing in importance and has frequently from 30 to 37 cells. The distribution of the reticular group is along the hinder part of the outer margin of the lateral horn, distinct from or continuous with the apical group, or it may extend inwards as a wedge with its base towards the formatio reticularis. Its cells are fairly large in size, and appear to be somewhat greater than those of the apical group. In the lower fourth of the segment there is interpolated between the apical and the reticular

c.C

FIG. 21 (D. 12, 172, L.).— The lateral horn is not pointed, but FIG. 22 (D. 12, 287, R.).—This figure shows an instance forms a long, full, rounded projection. The intermedio- where the reticular cells are present and the apical lateral cells form a continuous group along the whole margin series almost entirely wanting. of this swelling from the base of the anterior to that of the posterior horn. Apical and reticular cells are inseparable.

group a very large third group of cells, containing in some sections 30 cells. This group rapidly reaches a maximum, lasts for some 10 sections, and then rapidly disappears. It is present only on the left side, and the size of the cells is not essentially different from that of the other groups. The reticular group lies on a level with Clarke's column (fig. 24). The apical group is distributed in the spike-like tip of the lateral horn. Occasionally some of its cells pass along the anterior aspect; more frequently they stretch along the posterior border. There are occasional outlying cells in the white matter. Second Lumbar Segment.—This segment was divided into 208 sections. The inter- medio-lateral tract on the right side consists of 1464 cells and on the left of 1123. It somewhat resembled C. 8 in the rapid diminution in the number of its cells. As far as 126 DR ALEXANDER BRUCE

I Li.

FIG. 23 (L. 1, 29, L.).—The lateral horn forms a pointed projection. The apical and reticular cells are very numerous, and closely aggregated. The two series are continuous.

C. C

FIG. 24 (L. 1, 187, R.).—The lateral horn is pointed. The apical and reticular cells are numerous but form distinct groups. ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 127 section 130 there are small groups of 3 or 4 cells, and beyond this there may be other single cells whose nature it is impossible to determine with certainty. The cells lie at the margin of the grey matter, which is now in front of Clarke's column. There is no apex to the lateral horn, and no distinct definition in the three groups, apical and reticular. There are a few outlying cells below the second lumbar segment. A few cells are found in the third lumbar segment, which perhaps correspond to the intermedio-lateral tract, but the nature of which cannot be definitely determined.

Conclusions.—From the examination of the graphic representation of the cell-groups and of the microscopic sections, the following conclusions may be drawn as to the distribution of the cells of the intermedio-lateral tract:— 1. The intermedio-lateral tract may be defined as a tract composed of a special series of nerve-cells, situated at the outer margin of that portion of the grey matter which lies between the anterior and posterior cornua. These cells are not necessarily limited to the lateral cornua. 2. Within the spinal cord the tract is found in three regions: (1) in the upper cervical region as low as C. 4 ; (2) in the lower cervical, the dorsal and the upper lumbar regions; and (3) in the lower sacral region (below the lower part of the third sacral segment). 3. It is absent in the cervical enlargement from C. 5 to C. 7 inclusive, and in the lumbo-sacral region from L. 3 to the upper part of S. 3 inclusive. 4. In that portion of the tract which is at present under consideration—viz., the second of the above-mentioned divisions—its component cells are found mainly in two positions : (a) in the lateral horn proper, or in analogous positions above the level at which the lateral horn is fully constituted ; and (b) along the margin of that part of the grey matter which is in immediate relationship to the formatio reticularis, and also among the strands of the formatio reticularis itself. For convenience of description and reference these may be distinguished as the apical cells and the reticular cells. 5. The apical and reticular cell-systems have not a coextensive longitudinal distribution. 6. The apical cells are found between the middle of the upper half of the eighth cervical segment and the lower end of the second lumbar, or the extreme upper part of the third lumbar segment. 7. The reticular cells are first met with in the lower half of the second dorsal segment, and have the same lower limit as the apical series. They are not present in the cervical enlargement. 8. The upper part of the apical cell-series is composed of cells which are either situated in the white matter at some little distance behind the lateral part of the anterior horn, or are applied more or less closely to the grey matter. In all cases the cells are distinct from the large motor cells in their position, size, form, and grouping No transitional forms are anywhere found between the cells of the two series. 128 DR ALEXANDER BRUCE

9. The lateral horn is not fully constituted above the lower half of the first dorsal segment. This horn is not a transition from the lateral part of the anterior horn, but is a new and independent formation. It is represented in C. 8 and the upper part of D. 1 by the outlying cells of the intermedio-lateral tract. 10. The lateral horns of the two sides may show a want of symmetry in size and form, notably in the lower dorsal and lumbar regions. In the tenth, eleventh, and twelfth dorsal segments the apical cells lie in a plane posterior to the central canal. 11. The middle cells described by WALDEYER do not form any part of the inter- medio-lateral tract. 12. The cells of the intermedio-lateral tract vary in size from 12 M to 60 M. 13. The apical and reticular cells cannot be distinguished by any essential difference in their form, size, or structure. Large and small cells lying in close juxta- position may be present in both series in any one section. It has not been found that any group is composed entirely of large or of small cells. Large cells are relatively more numerous towards the lower end of the tract, but they are present alike in the apical and in the reticular series. 14. The number of cells in the intermedio-lateral tract is vastly greater than has hitherto been recognised. The following are the total numbers counted in each segment:— Left. Eight. c. 8 595 429 D. 1 1,867 1,720 D. 2 3,931 3,635 T). 3 7,297 7,471 D. 4 3,623 3,803 IX 5 7,958 7,407 D. 6 8,105 8,030 D. 7 8,739 8,282 IX 8 6,223 5,943 IX 9 9,011 8,987 1). 10 8,903 10,203 IX 11 6,261 + 6,498 + IX 12 7,888 8,545 L. 1 7,053 6,765 L. 2 1,123 1,464

Total ... 88,577 89,182 These figures are certainly below the total number. 15. The cells of the intermedio-lateral tract do not form a continuous column, but occur throughout the tract in groups or clusters. 16. These groups are not symmetrical on the two sides, although they may present a general resemblance to each other. There appears to be a larger number of cells on the left side in the lower cervical and upper dorsal regions. In the tenth dorsal segment there is a large excess on the right side. ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LA.TERAL TRACT. 129

17. These groups or clusters vary in size and form and in their distance from each other. 18. In each segment the cell-groups are arranged in a manner which may be regarded as characteristic of that segment. 19. The number of groups in each segment is somewhat difficult to determine in some cases ; generally the number is fairly equal on the two sides. 20. At the upper and lower extremities of the tract there is a tendency for the groups to appear suddenly, to rise rapidly to a maximum, and then quickly to disappear (see graphic chart). Towards the centre of the tract—below the fifth and above the tenth dorsal segments—the groups are less separated from each other. They rise slowly, persist for a considerable length, and diminish slowly. In this region the maximum number of cells attained is never so great as towards the extremities of the tract. 21. There is a remarkable increase in the number of the cells in the third dorsal segment. There is a marked transition in the form of the groups in the middle of the fifth dorsal segment, and another at the middle of the ninth dorsal segment. 22. The intermedio-lateral tract has a vascular supply largely independent of that of the motor cells of the anterior cornu. 23. The segmentation of the tract into groups or clusters of cells is not due to the distribution of blood vessels or of the root fibres, but is probably in some way related to their function. Although the present communication is intended to be a purely anatomical investigation, its main interest, of course, must be derived from our knowledge of its function, and of the pathological changes which it undergoes in disease. The researches of GASKELL and LANGLEY as to the outflow of the sympathetic fibres show that the distribution of these coincides in a remarkable manner with the distribu- tion of the cells of the intermedio-lateral tract. It is now certain that the column of CLARKE cannot be the source of the origin of these fibres, and if there is any spinal centre at all it must, by exclusion, be either the "middle cells" of WALDEYER or the intermedio-lateral tract, or both of these. This communication shows that where there is the greatest outflow of sympathetic fibres there is the greatest number of cells in the intermedio-lateral tract. The cervical sympathetic gets its largest supply of fibres from the portion of the cord included between the eighth cervical segment and the fifth or sixth dorsal segments—segments in which the groups are most rich in cells. Then the outflow of the splanchnics is largest in the lower dorsal region, and here again the number of cells markedly increases and the character of the groups changes. The researches of ANDERSON and HERRING, and of ONTJF and COLLINS, seem to point with considerable unanimity to the intermedio- lateral tract as being the source of the sympathetic fibres. It must be admitted, however, that other observers have found conflicting, and sometimes unintelligible, TRANS. ROY. SOC. EDIN., VOL. XLV. PART I. (NO. 5). 17 130 DR ALEXANDER BRUCE

results of the experiment of section of the nerve, and further researches are obviously needed. So far as could be ascertained from a mere anatomical examination, no clue as to differentiation of function of the various groups can be obtained from the form of their cells. There were no groups of cells distinguished by a special size or form of cell. There was, it is true, a tendency for the cells in the lower dorsal region to be larger than in the cervical and upper dorsal regions, but these large cells were intermingled with small ones, and nowhere was there any appearance of a group so distinctive as to suggest that its function was essentially different from a neighbouring group. It is of interest to note that although the total number of cells on the two sides was, as far as could be ascertained, fairly nearly equal, yet that in the cervical and upper dorsal region there was a preponderance in favour of the left side. In the tenth dorsal region, on the other hand, there was a very remarkable preponderance in favour of the right side. As yet little has been done to connect the pathological changes with disease. The intermedio- lateral tract appears to escape entirely in cases where there is a chronic degeneration of the anterior cornual cells in progressive muscular atrophy and in amyo- trophic lateral sclerosis. This may be due to a difference of power of resistance or to a difference of vascular supply. In one case it has been found to be degenerated in connection with erythromelalgia. It may be hoped that future research will succeed in explaining symptoms of visceral and vascular diseases hitherto imperfectly understood.

LITERATURE.

ANATOMY.

J. LOCKHART CLARKE, Phil. Trans., 1851, vol. ii. p. 613, and 1859, p. 445. WALDEYER, Abth. den- Konig. Akad. der Wissenschqft, Berlin, 1888. EDINGER, tjber den Bau der nervosen Centralorgane, 1889 and 1904. OBBRSTEINER, Der Bau der nervosen Centralorgane, 1896, p. 226. LBNHOSSEK, Der Bau des Nervensystems, 1895, p. 343. VAN GEHUCHTEN, Anatomie du Systeme Nerneux, vol. i. p. 352. TOLDT, Lehrbuch der Gewehlehre, 1888, p. 173. DEBIERRE, La Moelle Epiniere et I'Encephale, 1894, p. 60. SCHMAUS-SACKL, Pathologisches Anatomie des Biickenmarks, p. 6. SCHWALBE, Lehrbuch der Neurologie, 1881, p. 337. SHERRINGTON, "Out-lying Cells in the Mammalian Spinal Cord," Phil. Tram. Roy. Son., London, 1890. "The Lumbo-Sacral Plexus," Journ. Physiol, 1892, p. 694. MOTT, "The Bi-polar Cells of the Spinal Cord and their Connections," Brain, 1890, p. 433. ARGUTINSKY, " On a Regular Segmentation in the Grey Matter of the Spinal Cord in the New-Bom, and on the Middle Cells," Arch.f. mikros. Anat., vol. xlviii., 1897, p. 504. ONUP and COLLINS, Sympathetic Nervous System, 1900. FORD ROBERTSON, Pathology of Mental Diseases, 1900. ON DISTRIBUTION OF THE CELLS IN THE INTERMEDIO-LATERAL TRACT. 131

PHYSIOLOGY.

GASKELL, "Structure and Function of Visceral Nerves," Journ. Physiol., 1886 and 1889. J. N. LANGLEY, "On the Medullated Fibres of the Sympathetic," Journ. Physiol., 1892. QUAIN, Anatomy, 10th edition, vol. iii. part ii. » H. K. ANDERSON, "Central Origin of the Cervical Sympathetic Nerve," Journ. Physiol., 1902, p. 510. PERCY T. HERRING, "Spinal Origin of the Cervical Sympathetic Nerve," Journ. Physiol., 1903, p. 282. BIEDL, "The Splanchnic Centres," Wien. klin. Wochnschr., 1895, p. 915. JOSEF NOTTEBATJM, "Secondary Degeneration after Section of Cervical Sympathetic," Marburg, 1897. LAPINSKY and CASSIRER, " Spinal Origin of Cervical Sympathetic," Ztschr. f. Nereenheilk., vol. xix. CASSIRER, " Anatomy and Physiology of the Vaso-motor Tracts and Centres," 1901.

PATHOLOGY.

LANNOIS and POROT, " Erythromelalgia, followed by Gangrene of the Extremities," Rev. de Med., 1903, p. 824.

DESCRIPTION OF PLATE. Graphic representation of the arrangement of the cells of the intermedio-lateral tract in the various segments in which it is found. The numbers below the graph indicate tens of sections. The numbers placed at the left-hand side of each segment indicate tens of cells. + + + in the graph indicate that the number of cells was not ascertained. Trans. Roy. Soc. Edin. Dr ALEXANDER BRUCE on " Distribution of the Cells in the Intermedio-Lateral Tract of the Spinal Cord." VOL. XLV. C8 Dl

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