Paper - Description of a model showing the tracts of fibres medullated in a new-born baby’s brain

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Sabin FR. Description of a model showing the tracts of fibres medullated in a new-born baby’s brain. (1911) Amer. J Anat. 11(2): 114- .

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Description Of A Model Showing The Tracts Of Fibres Medullated In A New-Born Baby’s Brain

Florence R. Sabin

From the Anatomical Laboratory of the Johns Hopkins University

Eleven Figures

Introduction

In 1900 I published a description of a model of the medulla, pons and mid-brain made from a series of sections of the brain stem of a new-born babe.

In this model were shown first the form of the main nuclear masses and secondly, the form of the fibre tracts that had received their medullary sheaths, thus the study was based on the fact that the tracts of the central nervous system are successively medullated, as has been worked out by Flechsig, and was the result of the idea that at birth so few of the tracts have received their medullary sheaths, that it is possible to model them out and obtain apicture of their form. A clear picture of the form of such tracts as the lemniscus medialis and fasciculus longitudinalis medialis, even though it represent only one stage of development is of value from two standpoints, first in pointing the way toward a picture of the tract in the complicated relations of the adult brain, and secondly in leading toward an understanding of the modifications in form of the tracts as they shift in their relations in development.

1 Sabin, A Model of the Medulla Oblongata, Pons and Mid-brain of a New-Born Babe. Contributions to the Science of Medicine dedicated by his pupils to William Henry Welch, Johns Hopkins Press, 1900; and Johns Hopkins Hospital Reports,

vol. 9; and Atlas of the Medulla and Midbrain, The Friedenwald Company, Baltimore, 1901.


The series of sections from which the model was made, extended only just through the region of the mid—brain. It was the hope at that time, to procure a series of sections of the entire brain of the new-born babe so as to complete the modeling of the tracts into the thalamus and cerebrum. The especial goal was to throw some light on the form relation of the internal capsule. Since that time five series have been cut in this laboratory, three of the newborn brain, and two of the brain stem and basal ganglia of the adult. Of these series, three are in the sagittal plane, while one of the baby’s brain and one of the adult were cut in transverse series. The sagittal series of one of the adult specimens was cut by Miss Gertrude Stein. It has proved most valuable. Miss Stein made a model of the medullated tracts in one of the series of the new-born brain, but it proved that the gaps in the series were sufficient to prevent an interpretation of the model. From the series on which the present study is based, two models have been -made, the first one was by Dr. E. G. Gowans, of Salt Lake City, who modeled the thalamus and basal ganglia on one side. Unfortunately Dr. G-owans' work was unavoidably interrupted and as there was little chance that he would be able to take it up again, I have completed it. In studying Dr. Gowans’ model I found it hard to interpret the bundles in the thalamus without including those of the brain stem, and hence made a new model of the brain stem and thalamus of the other side of the same b1 ain. The figures are all taken from my model, but the study covers all the work done in this laboratory on this topic by Miss Stein, Dr. Gowans and myself. I am indebted to Miss Stein for series she prepared, and to Dr. Gowans both for the model and. for his study of the subject by which I benefit. The specimen from which the model was made was brittle and while in thick cellodin the brain stem cracked from the thalamus. The cellodin, however, was thick enough to hold the two parts in exact apposition, as can be seen in figs. 5 and 7. The plane of the section is oblique as can be seen in the same two figures, since the raphe is included in the sagittal section (see no. '61, fig. 5). This only increases the difiiculty in the piling of the model but does not affect its accuracy. I believe that the model does throw some light on two points, first, the form relations of the medial lemniscus and the fibres of the red nucleus in their relations to the thalamus, and secondly, on the form of the internal capsule in relation to the thalamus- and corpus striatum, notwithstanding the fact that much of the internal capsule is non-medullated.

The model is shown in a series of five drawings, three from the mesial aspect and two from the lateral. Fig. 1 represents a mesial View of the entire model and fig. 9 a lateral view. The other figures, namely, 3, 4 and 11, represent dissections of the model to show the various structures. The nuclei are represented in a solid tone, the non—medullated bundles are faintly streaked, while the medullated bundles have a blue tone. Fig. 2 is a drawing of the mesial aspect of a baby’s brain, given for the purpose of orienting the first three figures of the model, while fig. 10 is a View of a dissection of the pyramidal tract given to orient the lateral views of the model. Both figs. 2 and 10 are from a baby’s brains of which, however, we have no records of the age. It is obviously older than the one from which the model was made, in which the pyramidal tract is not at all medullated. Four figures of sections are given, two from the baby’s brain from which the model was made, and two taken at about the same level from an adult brain. In the description of the model I shall follow this plan. First,

I shall take up the medullated tracts beginning with the lemniscus medialis and the group of tracts associated with it. The various nuclei will be mentioned in connection with the fibre bundles. Secondly will follow a description of the form of the internal capsule, both the non—medullated and the medullated part, and thirdly, an account will be given of the nuclei of the thalmus, hypothalamus and corpus striatum, with the associated medullated bundles. The following table gives a list of all the medullated tracts found in the series in approximately the order in which they are taken up.


A. A group of fibres making up the main sensory tract to the cortex together with certain tracts associated with it by position: I. Seenfrom the mesial aspect 1.

2.

9°51:-’=P‘r>~

9.

Lemniscus mcdialis and rubro—lenticular tract (or fasciculus lenticularis of Forel)

Fasciculus gracilis and fasciculus cuneatus,——not modeled

Tracts from no. 2, forming the lemniscus medialis, namely: (a) Decussatio lemniscorum (b) Fibrae arcutae internee

Lemniscus lateralis

Lemniscus superior

Tract to the substantia nigra

Tract to the nucleus hypothalamicus (Corpus Luysi)

Tract connecting the nucleus colliculi inferioris with the center median of Luys

Tract connecting the nucleus hypothalamicus of Luys with the globus pallidus

II. Seen from the lateral aspect—

I.

2.

Tract from the ventro—lateral nucleus of the thalamus to the upper third of the posterior central gryus Lenticular nucleus to the same zone

B. The fasciculus longitudinails medialis and cornmissura posterior 0. Miscellaneous:

S°9°.“.°.°‘:*‘.°°.‘°1“

Fasciculus retroflexus of Meynert

Corpus restiforme or inferior cerebellar peduncle, not modeled

Brachium conjunctivum or superior cerebellar peduncle

Rubro-pontal tract

Forrnatio reticularis,—not modeled

Cranial nerVes,——not modeled

Small bundle at root of optic nerve

Optic fibres in relation to the lateral genticulate body

Certain fibres associated with the substantia nigra, the nucleus hypothalamicus of Luys and the globus pallidus of the lenticular nucleus.

The lemniscus medialis is shown best in the three views of the model from the mesial aspect, figs. 1, 3, and 4. The lemniscus begins at the transition between the spinal cord and the medulla, at the point where the decussatio lemniscorum crosses the middle line. In the series studied, the posterior columns of the cord (no. 2, fig.

7), Were medullated. but were not modeled.

The deoussatio

lemniscorum is a small compact bundle (no. 3, fig .1), which begins in the nucleus funiculi gracilis, curves around the edge of the gray matter bordering the central canal, and crosses the middle line at a point marked 4 in fig. 1. This point is Ventral to the central canal, just caudal to the inferior olive. Within the medulla, the bundle from the nucleus funiculi gracilis is joined by the more diffuse mass of internal arcuate fibres from the nucleus funiculi cuneati (no. 5, fig. 1.) These two crossed tracts make the lemniscus in the medulla, which is a broad band as seen from the mesial aspect. It lies close to the raphe, hemmed in between the two inferior olives. In. the pens, the lemniscus spreads out to the side making a narrow band in the mesial plane. In the lower part of the pens can be seen the position of the superior olive (no. 7, fig. 3), quite far to the side, and the lateral lemniscus emerging from it. Throughout the pens, the medial and lateral lemnisci are parallel. At the cerebral end of the pons, the lateral lemniscus curves still farther lateralward, and turns dorsalward to enter the nucleus of the inferior colliculus (no. 8, fig. 3).

The medial lemniscus, on entering the mid—brain shows a number of interesting points. In the firstplace, it gives off a small bundle which enters the caudal tip of the substantia nigra (no. 9, figs. 3, and 7). In using the term enters, it is not intended to assume the direction of the fibres since Weigert sections cannot give the relation to the cell body. Secondly, from the dorsal border of the medial lemniscus is given off the superior lemniscus which curves dorsalward parallel to the lateral lemniscus to enter the superior colliculus (no. 10, figs. 3 and 4). Thirdly, the entire mass of the medial lemniscus curves lateralward to make room for the red nucleus. This can be seen in fig. 1, but better in fig. 3, and best in fig. 4, from which the red nucleus has been removed. Lateral to the red nucleus, the lemniscus gives off a small bundle to the nucleus hypothalamicus of Luys, exactly similar to the one given off to the substantia nigra (no. 11, figs. 3, 7, and 8).

The relations of the lemniscus to the thalamus are complicated. It has been found that the fibres run to two nuclei, namely the center median of Luys, and the ventro-lateral nucleus. Here it may be well to enumerate the nuclei of the thalamus which can

be made out and modeled, though they will not be described until later: 1.18 FLORENCE R. SABIN

The nucleus medialis The nucleus anterior The center median of Luys and the cup-shaped nucleus The nucleus ventro—lateralis—

Medial part receiving the medial lemniscus

Lateral part connected with the cortex The nucleus dorso—lateralis not separated from the pulvinar The pulvinar The nucleus corporis geniculati medialis The nucleus corporis geniculati lateralis


In studying the relations of the lemniscus to the thalamus, I have found the Work of Forel2 most helpful and shall use his familiar terms. At the very beginning, however, it will be well to be clear about directions in the thalamus. In the first place, the brain stem of the baby is more nearly at right angles to a longitudinal axis of the cerebrum itself than that of the adult. Indescribing the thalamus the difificulty of orientation is familiar to all students of the subject and is due to the fact that the terms dorsal and ventral as applied to the cerebrum itself are not the same as dorsal and Ventral for the brain stem, and the thalamus comes at the point of transition. T shall use the terms “dorsal” and “ventral ” in the thalamus in exactly the same sense as in the brain stem, and hence shall speak of the lenticular nucleus as ventro—lateral to the thalamus. It will be Very necessary in following Forel’s desciption to note that his sections are frontal to the adult brain, and hence oblique in the baby’s brain. If, for example, a line be drawn through the pons, the red nucleus and the center median of Luys in my fig.'4 at about the direction indicated by lines 53, it will correspond in general to Forel’s fig. 5, plate 7. Therefore “dorsal” and “Ventral,” in the sense of ForeI’s figures, are at an oblique angle to mine.

To return to the relations of the medial lemniscus to the thalamus, as the lemniscus curves around the red nucleus (no. 13), it becomes impossible to separate it from fibres either from the red nucleus itself or from fibres of the brachium conjunc 2 Forel, Untersuchungen ueber die Haubenregion und ihre oberen Verknfipfungen im Gehirne des Menschen und einiger Saugethiere. Archiv fur Psychiatric und N ervenkrankheiten. Bd. 7, 1877.

tivum passing through the red nucleus. Emerging from the cerebral end of the red nucleus is a great mass of medullated fibres (see fig. 3), which soon divides into two bundles, a dorso—lateral mass which is Forel’s BaTh, (no. 12), and a more ventral and medial bundle which is Forel.’s Feld H. The dorso-lateral bundle which is Forel’s BaTh is a composite of possibly three elements, first, a part of the medial lemniscus, secondly, possibly fibres from the red nucleus and thiidly, a small bundle (no. 16), which comes from the nucleus colliculi inferioris and runs to the center median of Luys. This bundle is readily seen in its connections in the section of the baby’s brain in fig. 7, no. 16. It is readily identified in sagittal sections of the adult by the angle the bundle makes with the main mass of BaTh (see no. 12, fig. 7). The section of the adult brain (fig. 8), is, however, just too far lateral to show the two bundles as separate tracts. The bundle from the inferior colliculus to the center median of Luys is described by Dejerine,3 under the confusing name of “the arm of the inferior colliculus,” a term which should be reserved for the fibres connecting the inferior colliculus with the medial geniculate body. Dejerine, however, makes the distinction, in fact, and notes, that the bundle in question enters the center median of Luys. The true brachium quadrigeminum inferius connecting the inferior colliculus with the medial geniculate body is non-medullated at birth, and lies farther lateralward so that it is seen only from the side (no. 25, fig. 9).

The bundle BaTh (no. 12), then consisting of a part of the leminscus, the tract from the inferior colliculus and possibly of fibres from the red nucleus enters the cup‘ shaped nucleus (no. 15, figs. 8 and 11), and the center median of Luys (no. 14). In connection with these nuclei it is interesting to note that Sachs‘ found that in degeneration experiments involving the center median of Luys and the cup—shaped nucleus, there were no efferent fibres to the cortex nor to the mesencephalon; that the efferent fibres all ran to the other nuclei of the thalamus,

3 Dejerine, Anatomie d. centres Nerven, Tome 2, 1901, p. 72. 4 Sachs, On the Structure and Functional Relations of the Optic Thalamus. Brain, August, 1909, vol. 32, page 146.

those from the cup-shaped nucleus reaching all the thalamic nuclei except the anterior nucleus, those from the center median of Luys, reaching all except the anterior and medial nuclei. If these conclusions are correct, we may say that at birth, only the afferent fibres of these two nuclei are medullated and these af— feren.t fibres come from the medial lemniscus, the inferior colliculis and possibly the red nucleus. There are no other medullated bundles associated with these nuclei at birth.

The rest of the fibre mass (no. 17), which emerges from the red nucleus is likewise a composite mass. It lies farther Ventral and more medial than BaTh and corresponds to Forel’s Feld H. It is a mass of fibres, oval in cross section (see Forel’s fig. 11, plate 7), and made up of two parts, as can be seen in fig. 4, a lateral part (no. 18), Forel’s H1, which appears to be a direct continuation of the medial lemniscus, and a medial part (no. 19), Forel’s H2 which appears to emerge from the red nucleus, as can be best seen in figs. 1 and 3 of the model and in section in fig 6. The lateral part (no. 18), divides into a forked bundle which enters the ventro—lateral nucleus of the thalamus. The more Ventral bundle of the fork enters the external medullated lamina of the thalamus, as can be seen in the section of the adult brain in fig. 8. In the different figures the number is placed at the fork of the Y or on one or both branches. This is an exceedingly im portan.t bundle since it is a part of the main cortical path, which is now generally thought to consist of these three elements, the posterior columns, the medial lemniscus, and the thalamo—cortical radiation. In the model it will be readily seen that the ending of the main lemniscus (bundle in the thalamus agrees with Von Monkow’s5 description that the lemniscus ends in the caudal ventral part of the great‘ lateral nucleus of the thalamus. This ending of the lemniscus has been confirmed by Mott,“ more recently by Ramon y Cajal, quoted from Sachs, and by Sachs.7 Sachs speaks of the ending of the lemniscus as in the “Ventral third and lower (z'.e., caudal) half of the middle third of the lateral

5 von Monakow. Gehirnpathologie; N othnagel, Specielle Pathologie und Therapie, Wien. Zweite Auflage, 1905, S. 90-91. 6 Mott, Brain, 1895. 7 Sachs, ibid., page 130.

nucleus.” By comparing the three views of the model from the

mesial aspect it will be noted that this forked bundle of the lemniscus enters the medial part and the caudal surface of the ventr0— lateral nucleus. In fig. 1 is shown the rather thin medial nucleus, especially thin along the ventral border. This has been removed from figs. 3 and 4, showing the large lateral nucleus. The size is better estimated in fig. 4, from which the lateral nucleus itself has been entirely removed. A form relation of the medial lemnis— cus can be especially well seen in figs. 9 and 11, namely, that the medial lemniscus, throughout the superior colliculus region, lies close to the lateral surface in the groove between the crus and the colliculi, but the bundle being straight, it does not enter the extreme lateral part of the thalamus which projects so far to the side of the mid—brain.

The brain at birth then shows that the medial lemniscus, as far as it is medullated, enters two nuclei in the thalamus, the center median of Luys and the cup—shaped nucleus considered as one and the medial part of the ventro—lateral nucleus as the the other. Moreover, in connection with the ventro-lateral nucleus, the medullated bundle forms a part of the external medullated lamina. These relations will be clear by comparing figs. 7 and 8.

The relations of the more ventral part of Forel’s Feld H, namely, his fasciculus H 2, are especially well shown in the model. The bundle (no. 19, and its continuation, no. 20), appears to arise in the red nucleus. It emerges from the red nucleus, at its cerebral end, close to the mid—line, and, as is seen in figs. 3 and 4, takes the following course; it passes forward dorsal to the the nucleus hypothalamicus of Luys to a point just cerebralward to Luys’ body, where it curves sharply ventralward, along the medial border of the crus, and then turns first caudalward and then directrectly lateralward along the caudal surface of the first part of the globus pallidus. Within the globus pallidus this bundle is perfectly sharp in sagittal sections of the adult brain as can be seen by comparing no. 20 in figs. 7 and 8. It lies on the caudal surface of the globus pallidus, adjacent to the optic nerve. This bundle was described by Forel as H 2, and is called by Dejerines Le fetis “ Dejerine, ibid., vol. 2, page 327.


ceau lenticulaire dc Forel. In View of its relations, it would seem to me that it might be termed the fasciculus rubro-lenticularis of Forel. If one bears in mind the oblique plane of Forel’s sections as compared with the models it will be seen that his figures 17 and 18, plate 8, which run in the direction of the fibres of bundle 19 in my fig. 4, are in the very best plane to show the course of the lenticular fasciculus around the medial edge of the crus and into the globus pallidus. The same sections must also show, as they do, the lemniscus fibres within the external medullated lamina of the thalamus.

In this connection it will be well to make clear that the rubrolenticular fasciculus of Forel (H2) is not the same as Von Monakow’s9 dorsai Anthea? der Lmsenicernsciziénge notwithstanding the fact that he identifies it with Forels’ H2. From a study of Von Monakow’s figures 21-30, it is clear that he is dealing with two different bundles both of which he calls H 2. The first, which he identifies with Forel’s H 2, and labels mC], turns into the globus pallidus around the lateral border of Luys’ body while the true Forel’s fasciculus as shown in Forel’s figures and in the models curves around the mesial border of Luys’ body, and is shown in Von Monakow’s figs. 30-34, labeled H 2 and Lisch C. The bundle which. Von Monakow calls the dorsal Antheil der Linsenkemschlmge is also medullated at birth. It connects Luys’ body with the globus pallidus, but cuts directly through the crus at the lateral border of the nucleus hypothalamicus of Luys, instead of curving around the medial edge of the crus. This bundle will be considered in a moment, but it is not the same as the more medial fasciculus rubro—lenticularis which is not connected with the Luys’ body. Obersteiner” identifies the bundle which curves around the lateral border of the nucleus hypothalamicus of Luys as Forel’s H 2 thereby agreeing with Von Monakow. To the bundles which in the adult, curve around the mesial border of the crus and connect with the lenticular nucleus, Obersteiner gives the general name H irn schenkelschlinge. He identifies an ansa peduncularis (fig. 377), an ansa lenticularis and an unterer Tkalamus stiel (fig. 220); in the brain at birth only one bundle curving around the mesial border of the crus is medullated, namely, the rubro lenticular fasciculus which, I think should be identified with Obersteiner’s ansa peduncularis.


9 Von Monakow, Experimcntelle und pathologisch-anatomisch. Untersuchungen uebcr die Haubenregion, den Sehhiigel, und die Regio-subthalamica. Arch. f. Psych. u. Nervenkn, 27, 1875, S. 29.)

1“ Obersteiner, Anleitung beim Studium des Baues der Nervosen Centralorgane Vierte Auflage, Leipzig und Wien, Franz Deuticke, 1901, S. 377 u. 559, figs. 168220.


In connection with Forel’s field, Sachs gets a degeneration of Forel’s fasciculus from a lesion anterior to the red nucleus and terms the bundle the tractus rubro-globus pallidus which is probably the same as no. 19. He also finds a still more medial bundle, the inferior peduncle of the thalamus, which is entirely nonmedullated at birth. It may be added here that the ansa lenticularis is also non-medullated at birth.

The bundle just referred to in connection with the nucleus hypothalamicus of Luys, is not well illustrated in any of the views of the model, since it lies lateral to Forel’s fasciculus no. 19 and is nearly hidden by that bundle in the drawings. The hypothalamic nucleus is oval or lens—shaped, both in sagittal section (fig. 8), and in the familiar transverse sections such as are shown in Forel’s and von Monakow’s figures. It has a capsule of fibers, especially marked at the cerebral end (no. 23, fig. 7). At the lateral border of the Luys’ body, the fibres of this capsule cut through the crus, to the globus pallidus. Within the globus pallidus, these fibres lie close to the crus (no. 30, fig. 4) and are distinctly separated from the Forel’s rubro-lenticular fasciculus (no. 20, figs. 4 and 7). For this bundle connecting the Luys’ body and the globus pallidus, transverse sections are far better than sagittal. This is the bundle referred to by Von Monakow as the dorsale Antheil der L7.'nsenker— schlinge. It shows well in Forel’s fig. 12 and von Monakow’s fig. 26 as the dorsal capsule of Luys’ body, lying ventral to the zona incerta and curving through the crus to the globus pallidus. In the model, Luys’ body is seen to be connected with the medial lemniscus (no. 11) on the one hand, and with the globus pallidus, on the other hand, by the medullated bundle (nos. 23 and 30) just described.


To sum up, in the course of the afferent paths to the cortex, as far as they are medullated at birth, there are two great relay stations in the basal ganglia, the ventro—lateral nucleus of the thalamus and the globus pallidus of the lenticular nucleus. The paths are first the medial lemniscus. The medial lemniscus is the indirect continuation of the posterior columns of the cord. It arises in the medulla from two bundles of crossed fibres, one from the nucleus of the fasciculus gracilisand the other from the nucleus of the fasciculus cuneatus.“ It passes through the pens without giving off any bundles; in the mid—brain, it gives fibres to the substantia nigra, and the superior colliculus; in the thalamus it ends in the center median of Luys the cup—shaped nucleus and the ventro—lateral nucleus of the thalamus. Secondly, there are two systems of medullated tracts which connect the inner division of the globus pallidus with lower centers. One of these systems of fibres may be connected with the cerebellum, since the inferior cerebellar peduncle or corpus restiform is partly medullated, connecting the cord and the cerebellum, the superior cerebellar peduncle or brachium conjunctivum is medullated connecting the cerebellum with the red nucleus, and Forel’s lenticular f asciculus seems to connect the red nucleus with the globus pallidus. The second connection of the inner part of the globus pallidus is by the tract making a capsule for the hypothalamic nucleus of Luys which is also connected with the medial lemniscus. Thus the model shows two nuclei as relay, stations for cortical paths the medial part of the ventro—lateral nucleus of the thalmus, which is known to be a relay station in a sensory path, and the medial part of the first division of the globus pallidus which is, however, not so definitely known as a part of a sensory path. F lechsig regards this lenticular cortical path as ascending.” The cortical radiation as far as it is medullated at birth comes from these same two nuclei, but from their lateral portion. Thus there is a medullated bundle between the lateral part of the lateral nucleus (no. 26) of the thala 11 The decussating bundle from the sensory nucleus of the trigeminus is not present in this series. It was shown in my first model lying in the floor of the fourth ventricle just cerebralward to the nucleus n. absducentis. It was searched for with great care in the present series since Lewandowsky, in the Neurobiologische Arbeiten, herausgegeben von Oskar Vogt, Erster Band, Zweite Lieferung, 1904, page 93, has shown its importance as making the third bundle to form the lemniscus medialis.

1? Flechsig, Archiv. f. Anat. u. Phys, Anat. Abth.

mus, and the cortex, and between the lateral surface of the globus pallidus (no. 27) and the cortex. These two bundles make up the cortical radiation medullated in the specimen (no. 28). The gap between the lemniscus and the cortical bundle is best seen in fig. 4, the lemniscus being numbered 18, and the thalamo-cortical bundle, 26. For the globus pallidus, the fibres to the medial part are seen as 19 in fig. 4, while the cortical radiation no. 28 is far to the side and seen best in fig. 11.


The medullated part of the cortical radiation needs special description. It consists, as has just been said, of two parts, one from the lateral zone of the thalamus (no. 26, figs. 4 and 11), the other from the lateral part of the globus pallidus (no. 27, fig. 11). Beyond the border of the thalamus as seen in fig. 4, these two bundles are absolutely indistinguishable, and the fused mass makes the cortical radiation labeled no. 28 in all the figures. The thalamic part of the radiation is the less extensive at birth. It is shown best in fig. 4 as no. 26. Here it will be seen to be a curved bundle in the form of a figure 6. The caudal part Which, from the point of View of the eerebrum proper, is the Ventral part, curves around the lateral nucleus of the thalamus; the stem of the 6 lies in the external medullated lamina of the thalamus, which gradually joins and fuses with the general cortical radiation. In sections this thalamo-cortical bundle which is medullated at birth is well illustrated in the literature, in the new-born, by Barker” in his fig. 664 This section is from one of our series and shows the thalamic radiation labeled Th, in its positon just cerebralward to the lateral geniculate body The same figure shows the globus pallidus with its capsule of fibres which makes the lenticular part of the cortical radiation. In thisseries the cortical radiation ex— tends both to the anterior as well as to the posterior central eonvolution while in the one from which the model is made, has only the posterior central bundle medullated. In the adult, the first thalamo—cortieal bundle to be medullated is illustrated by Dejerine” in his second volume (page 310, fig. 282). The caudal curved part of the bundle (see fig. 4), which represents the fibres emerging from the nucleus, Dejerine describes as the triangular zone of Wernicke (see page 357).

13 Barker, The Nervous System. New York, D. Appleton & Company, 1899. First edition, page 1051, fig. 664. ‘4 Dejerine, ibid.


The medullated cortical radiation occupies the postertior limb of the internal capsule, and the models bring out certain fundamental points about the internal capsule which can be made clear from three figures, namely, 4, 9 and 11. To begin with fig. 4, the internal capsule consists of, two segments, the anterior limb no. 31, entirely non-medullated at birth, and the posterior limb, no. 28, partially medullated at birth. These two sheets of fibres, the anterior and posterior limbs, stand at an angle to one another; the anterior limb is at a slight angle to the median sagittal plane of the brain proper as can be readily seen in figs. 4 and 1 1. This point would of course be seen better in a View of the model taken from the dorsal surface of the cerebrum, but it is a point well-known in the adult. The entire posterior limb on the other hand in the brain at birth is in a plane exactly parallel to the median sagittal plane of the cerebrum and hence is a perfectly flat sheet in figs. 4 and 11. The anterior limb radiates out between the caudate nucleus and the lenticular nucleus. In fig. 4, if the eye follows the crus or cerebral peduncle (no. 24) forward, it will be seen that it spreads out into a sheet of non-medullated fibres between the lenticular nucleus and the thalamus. This sheet of non-medullated fibres which lies in the primitive groove between the diencephalon and the telecephalon is the knee of the internal capsule and contains the non-medullated pyramidal tract. The posterior limb of the internal capsule extends between the knee of the internal capsule (no. 36) and the tail of the caudate nucleus (no.32), as it curves around into the roof of the lateral ventricle. These limits are shown best in fig. 9. This point can be readily related to the adult brain in any dissection of the ventricles, for the knee is determined by the foramen of Monroe and the tail of the caudate is readily seen.


The zone in which the posterior limb of the internal capsule reaches the cortex is an especially interesting point. Since the posterior limb is a perfectly flat sheet in the model in a plane exactly parallel to the median sagittal plane, it reaches the cortex in the upper third of the central convolutions. Thus in a transverse section the posterior limb corresponds to the lateral border of the tail of the caudate nucleus, and the fibres first medullated are projected straight to the cortex in a sagittal plane parallel to the median sagittal plane and exactly midway between the edge of the lateral ventricle and the surface of the island of Reil. In the adult brain the plane of the primitive posterior limb of the internal capsule can be demonstrated by making a sagittal section along the lateral border of the caudate nucleus to the point where it curves around into the roof of the lateral ventricle. In all of the models there is a curious band labeled “no. 37” on the cortical radiation at the base of the central sulcus. This band shows both in Barker’s and in Flechsig’s figures, quoted above, and in all our series, thus it is probably f_a constant. I think that it is due to the fact that the fibres curve lateralward just at the base of the central sulcus, and from dissections of the fibres in the adult brain I think that this bend in the fibres in due to antero—p0sterior bundles of fibres near the median plane. With the exception of this slight bend at the base of the central sulcus the primitive posterior limb of the internal capsule consists of straight fibres, z'.e.,those that take the shortest possible course.

In the baby’s brain, the lenticular radiation covers the entire posterior limb (see fig. 4), while the thalamic radiation occupies the middle third (see also fig. 4). In this particular specimen the combined radiation extends only to the posterior central convolution; in the series shown in Dr. Barker’s figures, quoted above, also from a new-born, the radiation reaches the anterior central convolution as well, and this is true in brain figured by Flechsig” from the a baby born one-half a month prematurely, and which lived three weeks. I conclude, therefore, that the series from which the model was made has a less extensive cortical radiation than the usual brain at birth, and that, to represent the average, the medullated bundle should be extended into the anterior central convolution in the line 53 on fig. 4. From the series whichwe have, I do not think that any of this radiation, even the part to the anterior central convolution, belongs to the pyramidal tract, the latter being entirely non-medullated. I have, however, not sufficient evidence to determine whether this globus pallidus——cortical radiation is ascending or descending. Flechsig regards the entire radiation both to the anterior and to the posterior central convolutions as ascending. It is, I think, important here to identify the medullated projection bundles shown in the models with those described by Flechsig. In Flechsig’s summary as given on page 369, his oz bundle, consisting of a very few fibres from the globus pallidus (or possibly from the substantia nigra) to the upper third of the central convolutions and distinguished by early medullation, can not be separated from the rest in my series. The /3 bundle from the ventro—lateral nucleus to the upper third of the central convolutions is my thalamo—cortical radiation (no. 26); while the (3 bundle, consisting of the large mass of fibres from the globus pallidus to the same zone of the cortex, is the same as my no. 27. The combined thalamo—and lenticular—cortical radiation in one of our series reaches only the post central convolution; in the others, it reaches the anterior central as well as it does in Flechsig’s series. The rest of the medullated bundles of projection fibres described by Flechsig in foetuses up to 50 cm. long, and in the new—born, are not medullated in our series.


15 Flechsig, Einige Bemerkungen ueber die Untersuchungsmethoden der Grosshirnrinde, insbesondere des Menschen. Arch. f. Anat. u. Phys., Anat. Abth., 1905. Taf. 16, fig. 8.


There is one more bundle of fibres which, though, non-medullated, has a form relation to the internal capsule, namely, the stria medullaris thalami. In figs. 3 and 4, it shows as a band of fibres (no. 54), extending from the zone of the knee (no. 36) of the internal capsule along the border of the thalamus adjacent to the caudate nucleus. Its position with reference to the anterior nucleus of the thalamus is plain in fig. 1.

Thus, in the central nervous system in one specimen of a newborn babe we have medullated bundles which may be grouped into the following tracts. First, a sensory tract involving three elements, the dorsal columns of the cord to the nuclei of the dorsal columns, the medial lemniscus from the nuclei of the dorsal columns to the ventro—lateral nucleus of the thalamus, and the thalamo—cortical radiation from the ventro—lateral nucleus of the thalamus to the upper third of the posterior (possibly anterior as well) central convolution. Secondly, a tract having as one element the globus pallidus with cortical radiations reaching the same part of the cortex; the other connections of the globus pallidus bring two different medullated bundles the one relating it to the red nucleus and thus to the cerebellar tracts, the other relating it to the nucleus hypothalamicus of Luys, which in turn is connected with the medial lemniscus at birth.

This completes the description of the bundles medullated at birth, which make a part of the projection system. It will now be necessary, in order to present a complete record of this specimen, to describe the other bundles which are medullated though the model does not, for the most part, show any point in their form relations not shown in the previous model. The first of these tracts is a long tract, namely, the fasciculus longitudinalis medialis, whose relations as an optic—auditory reflex. path are certainly, in part, brought out by the tracts medullated at birth. The rest of the medullated bundles can be regarded only as fragments of tracts in the present state of our knowledge. The fasciculus longitudinalis medialis (no. 1) is essentially the same in this model as in the first model. That it is a continuation of the ventro—lateral funiculus of the cord can be seen in fig. 1. Almost its entire extent is shown also in fig. 2. In entering the medulla, it curves dorsalward with the central canal, to the floor of the fourth ventricle. Here it shows a slight curve corresponding with the pontal flexture, which is still visible. Within the midbrain, it forms a deep trough (no. 39, fig. 1), in which lies the nucleus of the oculornotor nerve. Just beyond this trough it is joined by the posterior commissure (no. 40, fig. 1), which decussates just dorsal to the aqueduct and joins the fasciculus longitudinalis medialis opposite the cerebral end of the red nucleus. The fascicluus longitudinalis medialis curves ventralward just in front of the red nucleus and comes to an end abruptly.


The fascilulus retroflexus of Meynert is one of the most conspicuous of the short tracts medullated early. It is a small compact bundle (no. 41), seen only in fig. 1, extending from the region of the ganglion of the habenula of the thalamus into the red nucleus. It could not be traced to a ganglion interpedunculare.


The corpus restiforme, or inferior cerebellar peduncle, is medullated and is shown as no. 42 in fig. 7. It was not included in the model, nor were the formatio reticularis fibres, nor the ct anial nerves, since they were all shown in the previous model and were not necessary here for orientation. The brachium conjunctivurn, or superior cerebellar peduncle is, however, included in fig. 1, (no. 45), because of its relations to a possible descending tract from the red nucleus (no. 46). There is a small bundle of fibres (no. 46), emerging from the caudal end of the red nucleus and extending into the pons just dorsal to the lemniscus medialis, near the median line. It cannot be followed far into the pons. Its relations are best seen by comparing fig. 1 and fig. 5. The sagittal sections are not adequate for determining whether this is a crossed path or not and the fibres cannot be traced below the upper fourth of the pons.


In connection with the optic nerve (no. 47), there is a tiny bundle of medullated fibres shown at the root of the nerve both in fig. 5 and in fig. 7. Its connections could not be traced~—I thought of a Gudden’s commissure, but it neither extended to the mid-line nor to the geniculate body. There is, however, a portion of the optic nerve medullated, as it enters the lateral geniculate body. This bundle is shown in the figure already referred to in Barker’s Nervous System.


The last of these rather indefinite medullated bundles, is the very small portion of the most medial part of the crus in the hypothalamic region containing a few medullated fibres. These fibres show in fig. 4, just lateral to Forel’s fascisulus (no. 19), extending on the one hand toward the substantia nigra and on the other to the little bundle of medullated fibres (no. 48), that separates the two parts of the globus pallidus near the median line. These fibres are most unsatisfactory for study in these sections. All that can be said is that they lie in the crus between three nuclei, the globus pallidus on the one hand and the hypothalamic nucleus of Luys and the substantia nigra on the other.

It now remains to describe the relations the various nuclei shown in the model. The nuclei of the mid brain require no special mention except that the form of the substantia nigra comes out better in these sections than in those of the other model where it was incomplete. The sagittal sections show its length, thatit is a thin mass curved to fit into the hollow formed by the crus, and that it extends to the nucleus hypothalamicus of Luys which is a small lens—shaped body lying between the zona inserta and the internal capsule. The cerebral surface of the substantia nigra is curved, indented as it were by the hypothalamic nucleus of Luys. Along the lateral border of the substantia nigra is a tiny medullated bundle, shown only in fig. 9, which appears to connect the substantia nigra with Luys’ body.


The nuclei of the thalamus that can be modeled out, are essentially those described by Burdach“ and more recently by Sachs, and Roussy.” In fig. 1, are seen especially the anterior and medial nuclei. Neither of them show any medullated fibres whatever. The medial nucleus (no. 55), covers the floor of the third ventricle; it can not be separated from the pulvinar, nor in sagittal sections at birth is it possible to separate it from the dorso—lateral nucleus along the dorsal border of the thalamus, as is plain in fig. 1. In the sections (figs. 5 and 7), it will be noted that there is a pale band, which represents non-medullated fibres extending forward from the center‘ median of Luys to the anterior nucleus (56) of the thalamus and separating the Ventro-lateral nucleus from the dorso—lateral nucleus. In the zone of the median nucleus this non-medullated band entirely disappears. The thickness of the medial nucleus from the middle line toward the side, is only a very small proportion of the width of the thalamus, as can readily be seen in fig. 1, since the caudal part of the nucleus has been cut away to expose the center median of Luys and the Ventro-lateral nucleus. In the zone just cerebralward to the center median of Luys, the medial nucleus is thicker than it is along the ventral border in fig. 1, and hence it is seen in sagittal sections at the level of Dejerine’s fig. 269, vol. 1.


1° Burdach, Bau und Leben des Gehirus. Leipzig. 1822. Dykschen Buchhandlung. Bd. 2. 17 (Roussy, La Couche Optique, Paris. G. Steinbeil, Edituer, 1907.

The Ventro-lateral nucleus of the thalamus is the largest mass of cells. It is shown best in fig. 3, from which the medial nucleus has been removed and some of the dorsal—lateral nucleus and pulvinar have been cut away. The extent of the ventro—lateral nucleus is best estimated in fig. 4, from which it has been entirely removed, the fibre mass, consisting of the knee of the internal capsule and external medullated lamina on the ventro—lateral aspect, and the posterior limb of the internal capsule on the lateral surface, making a shell in which the nucleus rests. The ventrolateral nucleus is separated from a dorsal nucleus, which is the do1'so-lateggmal nucleus and pulvinar together, by a band of nonmedullated fibres which is plain in the newborn (see no 57, figs. 5 and 7), but not at all sharp in the adult (see fig. 8), on account of the great number of medullated fibres. In fig. 8, the ventrolateral nucleus and the combined dorso—lateral nucleus and pulvinar are imperfectly separated, by the fact that there are more medullated fibres in the ventro—lateral nucleus than in the dorsal mass. As has been described, the ventro—lateral nucleus has two sets of medullated fibres at birth, first the bundle from the medial lemniscus (no. 18), which enters the caudal part of the nucleus, near the median plane just Ventral to the center median of Luys. A part of this bundle spreads out in the external medullated lamina. Secondly, the medullated cortical bundle (no. 26) emerges from the extreme lateral surface of the nucleus and helps make up the cortical radiation.


The dorso—lateral nucleus of the thalamus (no. 58), cannot in any way be separated from the pulvinar (no. 51). These two nuclei make a common mass of cells as can be well seen in fig. 5, the term pulvinar being simply used for the caudal part of the mass. Far to the side, as seen in fig. 3, the dorsal mass of the thalamus is less extensive, inasmuch as it lies wholly dorsal to the center median of Luys, than it is near the median plane, as can be seen in fig. 5, in which it lies not only dorsal to the center median of Luys but anterior to it as well. In fig. 3 it will be readily understood that the part labelled 58, and indicated by striation, is the cut surface of the dorso—lateral nucleus, the part which fits over the oblique surface of the ventro—lateral nucleus having been cut away. Thus the ventro—lateral nucleus is bounded on its median surface partly by the median nucleus and partly by the dorsolateral nucleus (fig. 3). The dorso—lateral nucleus is entirely non-medullated at birth.


The pulvinar (no. 51), as has just been said, is the projecting caudal part of the dorso-lateral mass. Its caudal boundary is the posterior commissure (no. 40, fig. 1) ;ventrally it is readily marked off from the center median of Luys (fig. 3) and laterally it extends to the taenia semicircularis (fig. 1), but it has no cerebral border, since it is continuous with the dorso—lateral nucleus (figs. 3 and 5).


On the lateral surface of the thalamus are the two geniculate bodies, the medial and lateral. They are both oval masses of cells whose form is well seen from the surface (nos. 49 and 50, fig. 9). The medial geniculate body has no medullated fibres in this series but the lateral geniculate body has a band from the optic nerve which in part spreads on to the surface, but which for the most part curves around the inner border, just caudal to the medullated thalamo—cortical bundle. This shows in the figure quoted above from Barker. A part of these fibres seem to enter the geniculate body, a part the pulvinar.


The center median of Luys is well shown in figs. 1, 3, 4. It is an oval mass of cells which lies in caudal part of the thalamus near the median line. It is just dorsal in position to the red nucleus, lateral to the fasciculus retroflexus of Meynert and lies between the medial nucleus, the ventro—lateral nucleus and the pulvinar. It fits into the cup—shaped nucleus as can be best seen in fig. 11, and in common with it receives a mass of medullated fibres consisting of a part of the medial lemniscus, possibly of fibres from the red nucleus, and of a small tract from the nucleus of the inferior colliculus. It has no other medullated tracts at birth.


This corpus striatum is of course made of the well known parts, the caudate and the lenticular nucleus. The form of the caudate, with its swollen head and its curved tail is Well known and can be readily seen in the models. The best way to obtain an idea of the caudate nucleus is to take an adult brain well hardened in formalin and shell the nucleus out from the bed of fibres, the internal capsule, on which it rests. The form, and the relations of the lenticular nucleus are much harder to make out. Starting from the lateral view of the baby’s brain (fig. 10), the lenticular nucleus underlies the island of Reil and hence it will be seen that it lies for the most part in front of the thalamus, which is its original position. As seen from the side, the lenticular nucleus or its lateral portion, the putamen, is a great oval mass of cells (fig. 9); the antero-posterior diameter is slightly greater than the dorso-ventral, speaking in terms of the cerebrum, and close to the optic nerve is a small tongue of the nucleus which extends into the temporal lobe. In the curve -of this tongue is the non-medullated anterior commissure.


Since the lenticular nucleus is best known as it appears in horizontal sections of the gross brain, it would be most readily understood by a dorsal View of the model, that is, a View taken from the dorsal surface of the cerebrum. The form of the nucleus in the new-born corresponds with its form in the adult as can be seen by comparing the description with horizontal sections of the adult. As seen from the convex surface of the cerebrum, the lenticular nucleus is a triangular mass, divided into three sections by bands of fibres for the most part non-medullated. The outer division, the putamen, is thelargest, it projects farthest toward the dorsal surface of the brain and also extends farthest ventralward. It is crescent in shape with the anterior end much larger than the posterior. Next comes the outer part of the globus pallidus, which is likewise crescent in shape with a swollen anterior end. The inner part of the globus pallidus is rectangular in shape. The medullated fibres are all associated with this inner division of the globus pallidus; starting with the median plane, there are a few medullated fibres between the anterior end of the two parts of the globus pallidus (no. 48)" ; secondly, there is a mass of fibres within the medial part of the globus pallidus at its posterior or caudal end (no. 30), the fibres lying adjacent to the crus as seen in fig. 4, and thirdly, there is the lateral capsule for the inner division of the globus pallidus which is the place of origin of the lenticular cortical radiation previously described (no. 27). If the lenticular nucleus be now viewed again from the mesial aspect it will be seen that the band of fibres, for the most part non-medullated, which separate the three divisions, all connect (see 48, fig. 4), with the anterior limb of the internal capsule, so that if these bands of fibres be considered, there are two curved sheets of fibres which spread out from the lateral surface of the anterior limbs of the internal capsule and these two shells of fibres separate the parts of the internal capsule. Thus, from the standpoint of the corpus striatium, there are three sheets of fibres, one separating the caudate nucleus from the putamen, the other two separating the three parts of the lenticular nucleus, and these three sheets of fibres meet in the sheet of fibres which makes up the knee of the internal capsule. There is no doubt that the form of the internal capsule can be made much plainer by models of the medullated bundles in series of later stages.

Explanation of Figures

KEY TO REFERENCE NUMERALS

Fasciculus longitudinalis medialis Fasciculus cuneatus Decussatio lemniscorum Point of crossing of the decussatio lemniscorum Fibres arcuatae internae Lemniscus medialis Nucleus olivaris superior Lateral lemniscus Tract of the medial lemniscus to the substantia nigra Lemniscus superior Tract of the medial lemniscus to the nucleus hypothalamicus (Corpus Luysi) Lemniscus medialis at the point of Forel’s BaTh Nucleus ruber Center median of Luys Cup-shaped nucleus Tract connecting the nucleus colliculi inferioris with the center median of Luys and for~ ming a part of Forel’s Ba’./‘h Combined mass of fibres from the lemniscus medialis and from the red nucleus (rubro-lentic— ular tract) making Fore1’s Feld H Lemniscus medialis to the ventro lateral nucleus of the thalamus, Forel’s Feld H, Rubro—lenticular tract, Forel’s Fcld H2 Rubro-lenticular tract, Forel’s Feld H2 within the first or medial part of the globus pallidus of the lenticular nucleus Ventro—lateral nucleus of the thalamus

22 23 24 25 26 27 28

29

30

31

32 33

34 35

36 37

38 39 40 41

42 43 44

Nucleus hypothalamicus (Corpus Luysi)

Medullated bundle following the cerebral surface of the nucleus hypothalamicus

Pedunculus cerebri or crus

Brachium quadrigeminum inferius

Thalamo—cortical radiation

Lenticular—cortica1 radiation

Cortical radiation made up of the two elements nos. 26 and 27

Small medullated bundle in the crus with transverse fibres connecting Luys’ body with the globus pallidus

Medullated fibres Within the globus pallidus connected with Luys’ body

Anterior limb of the internal capsule

Nucleus caudatus

In-ner division of the globus pallidus of the lenticular nucleus

Putamen of the lenticular nucleus

Anterior commissure, which in fig. 4 marks the line between the putamen and the globus pallidus

Knee of the internal capsule

Band at the base of the central Sulcus

Sulcus centralis (Rolandi)

Position of the nucleus 11. III

Posterior commissure

Fasciculus retro-flexus of Meynert

Corpus restiforme

N. V

N. VI 45 46

47 48

KEY TO REFERENCE NUMERALS

(CONTINUED) Brachium conjunctivuxn 56 Tract extending between the red 57 nucleus and the pons Optic nerve Medullated lamina. between the 58 two divisions of the globus pallidus Corpus geniculate medialc Corpus geniculate latex-ale 50 Pulvinar Subtantia nigra 60 Approximately the direction of 61 Forel’s fig. 5, plate VII 62 Stria mcdullaris thalami 63 Nucleus medialis thalami 64

Nucleus anterior thalami

Non—medullated lamina between the ventro-lateral and demolateral nuclei of the thalamus

Nucleus dorso-lateralis thalami. In fig. 3 this nucleus is striated to indicate that it is a cut sur« face

Line of thcco-rtex of the. antorim' central convolution

Nucleus colliculi inferioris

Raphe

Fornix

Maminillary burly N. III PLATE 1 TRACTS OF FIBRES MEDULLATED IN BABY'S BRAIN

Fig. 1 Mesial view of the entire model showing the tracts that are medullated at birth as far as they can be seen from the mesial plane. 2%><. This View shows especially the fasciculus longitudinalis medialis, the lemniscus medialis in the brain stem, and the anterior and medial nuclei of the thalamus. For the meaning of the numbers see key to numerals. An outline of the cortex of the anterior and posterior central convolutions is given for orientation. The bundles of mcdullated fibres have a. blue tone.

Fig. 2 Mesial view of a baby’s brain given to orient figs. 1, 3, and 4. The brain is older than the one from which the models were made.


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Fig. 5 Sagittal section of the brain stem and basal .ganglia. of the new-born ba.by’s brain from which the model was made taken near the mesial plane and showing especially the Iemniscus medialis no. 6, and the fasciculus rub1'o-1enticularis of Forel (no. 19). 2X.


Fig. 6 Sagittal section of the pons, mid-brain and thalamus of an adult brain in about the same plane as fig. 5, to show especially the relationsof the red nucleus to the lemniscus medialis and to the rubro-lenticular tract. About 1%><.

Fig. 7 Sagittal section of the brain stem and basal ganglia of the new-born ba.by’s brain from which the models were made, taken farther lateral than fig. 5, to show the relations of the lemniscus medialis (nos. 6, 12 and 18), to the thalamus. 2X.


Fig. 8 Sagittal section of the brain stem and basal ganglia, of an adult brain at a level slightly farther to the side than fig. 7. About 1%><.

Fig. 9 Lateral view of the entire model showing especially the position of the lemniscus medialis (no. 6) with reference to the surface form of the mid-brain, and the putamen and the cortical radiation medullated at birth. 2%><.

Fig. 10 Lateral View of the baby’s brain shown in fig. 2, showing a dissection of the pyramidal tract. This is not the cortical radiation medullated at birth (no. 28), but is, in general, parallel to it. The position of the pyramidal tract is indicated on fig. 9 by the arrow 36.


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Cite this page: Hill, M.A. (2019, August 20) Embryology Paper - Description of a model showing the tracts of fibres medullated in a new-born baby’s brain. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Description_of_a_model_showing_the_tracts_of_fibres_medullated_in_a_new-born_baby%E2%80%99s_brain

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