Book - An Atlas of the Medulla and Midbrain 4
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Sabin FR. and Knower H. An atlas of the medulla and midbrain, a laboratory manual (1901) Baltimore: Friedenwald.
|Florence Rena Sabin (1871 - 1953) and her collaborator presents one of the very earliest atlases of the human central nervous system, describing the midbrain and brainstem. This atlas was extremely useful for later researchers attempting to both understand the development and mapping of the midbrain and medulla. Florence Sabin later work was as a key historic researcher in early 1900's establishing our early understanding of both vascular and lymphatic development in the embryo.
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Chapter IV. Cerebellar Peduncles
1. Corpus Restiforme, or Inferior Peduncle
The description of the dorsal and lateral funiculi of the cord Restifom body, leads naturally to the corpus restiforme (Fig. 33), or inferior cerebellar peduncle, inasmuch as, at this stage of medullation, it receives most of its fibres (1) from the direct cerebellar tract of the lateral funiculus, and (2) from the dorsal external arcuate fibres of the dorsal funiculus. The fibrse olivocerebellares are nonmedullated. The view of the model from the lateral surface shows the relation of the corpus restiforme to the spinal cord, as well as its position with reference to the cerebellum and the other two cerebellar peduncles (Plate n). The superior cerebellar peduncle, or brachium conjunctivum, is shown clearly.
The corpus restiforme, as seen from the side is a great sheet of fibres continuous with the capsule of the nuclei of the dorsal funiculus (Plate n). Reference has already been made to the direct cerebellar tract how it forms a ribbon on the edge of the cord, how this band narrows on entering the medulla oblongata, passes cerebralward as a compact bundle, then turns dorsalward 1 to join the dorsal external arcuate fibres to form the corpus restiforme.
Plate ii illustrates a point Flechsig has made, that the direct cerebellar tract in the spinal cord lies ventral to the dorsal horn, while the corpus restiforme in the medulla oblongata lies lateral to the tractus spinalis nervi trigemini, which represents the upward continuation of the dorsal horn. 2
1 In this dorsal course the fibres are called fibrae transversales externae posteriores by v. Koelliker.
Tlechsig, P., Die Leitungsbahnen im Gehirn und Ruckenmark, Leipzig (1876), S. 325.
In passing cerebralward the corpus restiforme becomes narrower, forming a compact bundle which passes between the nuclei of the cochlear nerve laterally, and the descending tracts of the vestibular and trigeminal nerves medially. Just proximal to the level of the nucleus nervi abducentis the bundle turns dorsalward to enter the cerebellum and hence is not shown in the model. In entering the cerebellum, the corpus restiforme spreads out markedly. It lies lateral to the brachium conjunctivum and passes dorsalward and cerebralward while the latter passes dorsalward and spinalward. The two bundles then form an angle in which lies the corpus dentatum.
The corpus restiforme at this stage of medullation contains three sets of fibres, 1 (1) the direct cerebellar tract, (2) the dorsal external arcuates, and (3) fibres connecting the vestibular nerve with the cerebellum. This third group will be described in connection with the nerve. In the sections used in making the model the lateral portion of the corpus restiforme, corresponding, according to Flechsig, 3 to the fibrse cerebelloolivares is a non-medullated area (Fig. 33).
Restiform body The corpus restiforme was shown in longitudinal sections in connecions - tion with the nuclei of the dorsal funiculi of the cord (Figs. 6, 7 and 9). The first two sections show the relations of the dorsal external arcuate fibres while the third shows the direct cerebellar fibres in their dorsal course. They can be seen also on the right side of Fig. 12, lateral to the tractus spinalis N. trigemini. The connection with the lateral funiculus is made at the level of Fig. 16, which is just ventral to the substantia gelatinosa (Rolandi).
In the transverse series the corpus restiforme can be traced from the spinal cord to the vermis of the cerebellum (Figs. 25 to 37). The sections in Figs. 25 to 28 show the direct cerebellar tract; while Fig. 28 shows the nucleus of Blumenau which gives origin to the dorsal external arcuates. The direct cerebellar fibres in their dorsal course are seen in Fig. 30, and beginning of the corpus restiforme is on Fig. 31. In Fig. 33 the corpus restiforme lies between the cochlear nuclei and the descending tracts of the trigeminal and vestibular nerves. The section in Fig. 35 is taken at the point where the inferior cerebellar peduncle turns to enter the cerebellum opposite the proximal end of the corpus dentatum; while Figs. 36 and 37 carry the corpus restiforme to the vermis.
2. Brachium Conjunctivum or Superior Peduncle
Brachium The brachium conjunctivum (Figs. 33 and 46), or superior cerebellar peduncle, is shown in four views (Plates n, in, iv and vin).
J v. Bechterew gives five sets of fibres in the corpus restiforme, the three mentioned above, (4) fibres from the nuclei laterales and (5) from the nucleus olivaris inferior, v. Bechterew, W., Arch. f. Anat. u. Phys., Anat. Abth., Leipz. (1886), S. 403-410.
2 Flechsig, P., Die Leitungsbahnen im Gehirn und Eiickenmark, Leipz. (1876), S. 329.
In order to illustrate the decussations, the peduncles of both sides have been modeled. The origin of the fibres cannot be seen, inasmuch as the corpus dentaturn was removed with the cerebellum. However, the position of this nucleus and its relations to the superior and inferior peduncles can be determined by a study of Fig. 52 in connection with the transverse series. The level of section 146, Fig. 33, can be found on Fig. 52, and this section passes through the corpus dentatum and both peduncles. Section 182, Fig. 36, shows the peduncles but is at a level proximal to the nucleus. The corpus dentatum, then, lies in the angle between the corpus restiforme and the brachium conjunctivum. From this nucleus, the superior peduncle can be traced to its decussation in the pars dorsalis pontis. Proximal to the decussation, the peduncle on the left side has been sacrificed to other structures, while on the right, the peduncle alone has been modeled (Plate vin).
For a more detailed study of the brachium conjunctivum, the view from the dorsal surface gives the best starting-point (Plate in). On the right side of the figure the superior peduncle is dissected out; on the left it appears as a narrow band placed obliquely in the long axis of the pons (Fig. 6, Br. conj.). The band is straight save at the distal end, where it turns out slightly.
In the views of the lateral surface of the model (Plates n and iv), the peduncle can be traced toward its decussation. The band on the dorsal surface was really the edge of a sheet which passes ventralward, inward and slightly cerebralward. This sheet is not of uniform thickness, for its proximal border grows thicker as it passes ventralward; moreover, its surface curves lateralward, thereby increasing the distance between the two peduncles.
Eeference was made in connection with the dorsal view to the flaring out of the distal end of the band. Plate 11 shows that this portion of the band meets the nucleus 1ST. vestibuli superior, a connection which is clear in the sections (Fig. 7). On the other hand the proximal border of the lateral sheet is made of a small bundle of fibres distinguished from the main mass by their direction (Plates iv and vin, Brachium conjunctivum, dorsal bundle). Opposite this group of fibres is a small bundle which crosses from the lemniscus lateralis to the brachium conjunctivum (a on Plates HI and vm).
The brachium conjunctivum of the model represents not one, but at least three different fibre masses. (1) A distal bundle connected with the nuclei N. vestibuli superioris, (2) the main mass of fibres from the corpus dentatum which decussate at a ventral level, and (3) a small bundle which runs in the proximal border and decussates at a more dorsal level. This group of decussations makes a complicated structure in the model difficult to describe.
It may simplify matters slightly to mention at the outset two morphological features. First, the main bulk of the decussation of the brachium conjunctivum lies far ventralward and cerebralward, and thereby comes into relation with the nucleus ruber; secondly, that between the superior peduncles of the two sides in the pons is a wide area in which are situated masses of gray matter belonging to the formatio reticularis grisea. In Plate vm it will be seen that the decussating mass makes a hollow shell in the floor of the pars dorsalis pontis. This shell is open toward the dorsal aspect. Its sides are formed by the curved lateral sheets. The distal borders of these sheets project medialward as a sharp ledge and extend ventralward to a decussation that makes a distal wall for the shell (Plate vm). The sides of the sheet decussate both in the floor of the shell and in its proximal wall. The floor of the decussation is very thin, for the proximal wall receives the most of the fibres. As has been said, this wall seems to be made of two different masses of fibres (Fig. 44). A simple difference in direction of the fibres at the point of decussation might not be sufficient evidence to determine two masses, but in the transverse sections it is possible to distinguish the smaller dorsal mass, as it lies in the border of the sheet to a point where it is joined by a small bundle of fibres from the lateral lemniscus (a). The fibres of the dorsal bundle of the brachium conjunctivum are coarser than those from the lateral lemniscus.
It now remains to trace the superior peduncle to its destination. The proximal wall of the decussation almost touches the dorsal part of the nucleus ruber, and the fibres after crossing either pass directly into the nucleus or spread over its dorsal surface to help to make a capsule (Plate viii). Of the fibres which enter, some end in the nucleus, while a distinct bundle passes through. It will be noticed that on the right side of the model, the curve of the capsule represents the position of the nucleus. The nucleus itself was not modeled, as it was desired to indicate better the disposition of the fibres within. This will be made clear in the description of the nucleus itself.
In Figs. 33 to 48 the brachium conjunctivum can be seen in its rela- Brachium tions to the corpus deritatum. In Fig. 36 the superior vestibular nucleus lies immediately adjacent to the distal part of the peduncle, that is, to that portion of it which represents the decussation between v. Bechterew's nuclei. In tracing the series farther cerebralward, the superior cerebellar peduncle is seen to pass ventralward, while the inferior peduncle passes dorsalward (see Figs. 37-38, etc.). The succeeding sections illustrate the points brought out in the model. The ventral course of the fibres, the curve, and the wide space between the lateral walls, are all clear. Fig. 42 shows the cross-bundle extending between the lateral lemniscus and the brachium conjunctivum. The fibres of the commissure between Bechterew's nuclei cross in Fig. 43, while in Fig. 44 the decussating fibres in the floor of the shell are seen. Still farther forward (Fig. 46) the proximal wall is reached, and here the distinction in its dorsal and ventral parts is evident. The ventral part of the decussation can be traced through Fig. 47 and its relation to the nucleus ruber becomes evident in Fig. 48. The decussating fibres seen at this level just ventral to the nucleus N. oculomotorii belong to Meynert's decussation, while the most ventral fibres are those of Forel's decussation. The dorsal bundle of the brachium conjunctivum can be traced from Fig. 42 to its decussation on Fig. 46. In Fig. 42 it lies opposite the bundle crossing between the lemniscus lateralis and the brachium conjunctivum.
In the longitudinal series these relations are still more clear (Figs. 4 to 19). The brachium conjunctivum, in the wall of the velum is seen in Fig. 4. From here it can be traced ventralward to its decussation. In Fig. 6 is the cross-bundle between the lemniscus and peduncle; in Fig. 7 the relation to the vestibular area is clear, while in Fig. 9 the two ends of the band are characteristic, the distal edge sharp and projecting, the proximal edge full and round.
The section in Fig. 13 shows the dorsal bundle of the brachium conjunctivum. This section illustrates the nuclear masses of the formatio reticularis between the walls of the peduncles. Section, Fig. 16, shows a wide decussation; it includes the distal wall, or Bechterew's decussation, together with the floor and proximal wall or the brachium conjunctivum proper. This section, together with Fig. 17, shows the relations of the peduncle to the red nucleus. One very definite group of fibres lies immediately adjacent to the lemniscus medialis in Forel's Feld BATh. Fig. 19 brings out the fact that the fibres that enter the medial part of the red nucleus end there, while the more lateral fibres pass through. 1
1 The model of the brachium conjunctivum illustrates well the work of v. Bechterew in dividing the brachium conjunctivum into sections. The decussation between the superior vestibular nuclei corresponds with his description; the dorsal bundle agrees with his dorsal bundle while the ventral part of the decussation in the model includes his second and third systems.
(1). v. Bechterew, W., Die Leitungsbahnen im Gehirn und Biickenmark. Leipz. (1894), S. 135.
(2). The lateral descending cerebellar bundle of Ramon y Cajal was not found in the sections. Eamon y Cajal. Op. cit., S. 20. 4
3. Brachium Pontis, or Middle Peduncle
The brachium pontis or middle cerebellar peduncle is nonmedullated at the stage here considered, and hence its location must be imagined from the position of the pons.
The description of the larger fibre masses of the model is now complete. The central fibre mass, consisting of the medulla sheet and all of its continuations in the pons and midbrain, made the foundation for the model. By it the cord is connected with higher centres in the thalamus and the cortex. It includes also a specialized formatio reticularis bundle that connects a group of cerebral nerves, as well as a more general bundle that makes connections with the pons and midbrain at least. Each of the funiculi of the cord has been traced as far as its fibres are medullated and the relations of each to the central fibre mass have been demonstrated. The cerebellum has been related both to the cord and to higher centres by means of the corpus restiforme and the brachium conjunctivum. It remains now to trace the relation of the gray matter of the spinal cord to the nuclei of the cerebral nerves, to study the formatio reticularis and to consider the large ventral nuclei of the model.
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An Atlas of the Medulla and Midbrain (1901): Chapter I. Introductory | Chapter II. The Long Tracts | Chapter III. The Columns Of The Spinal Cord | Chapter IV. Cerebellar Peduncles | Chapter V. The Cerebral Nerves And Their Nuclei | Chapter VI. The Cerebral Nerves And Their Nuclei (Continued). Lateral Group | Chapter VII. The Inferior And Accessory Olives | Chapter VIII. The Midbrain | Chapter IX. The Formatio Reticularis Alba And Grisea | General Summary of what Is shown In Reconstruction | References To Literature | Abbreviations | Description of Figures and Plates
Cite this page: Hill, M.A. (2020, October 30) Embryology Book - An Atlas of the Medulla and Midbrain 4. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_An_Atlas_of_the_Medulla_and_Midbrain_4
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