Book - An Atlas of the Medulla and Midbrain 7
|Embryology - 17 Feb 2020 Expand to Translate|
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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 VII. The Inferior and Accessoey Olives
1. Nucleus Olivaris Inferior
inferior Position. The surface form of the olive, as seen on the uncut medulla, is shown in all text-books (Fig. 33). Its position in the reconstruction is seen on Plates n, in and iv. The nucleus itself extends from the proximal limit of the decussatio pyramidum to the pons (Fig. 20). It lies in the ventral portion of the medulla oblongata, lateral to the stratum interolivare lemnisci, from which it is separated by the root-fibres of the N. hypoglossus and the median accessory olive. Dorsal to the olive lies the large area of formatio reticularis in the medulla oblongata, but the lateral and ventral aspects of the olive are superficial. Opposite the distal half of the lateral surface is a considerable mass of medullated fibres belonging to the lateral funiculus of the spinal cord, but only one small bundle of these fibres extends opposite the proximal half of the olive (Plate iv).
The dimensions of the olive are as follows: The dorsoventral diameter 4.48 mm., the transverse 6.5 mm., and the anteroposterior 7.5 mm.
The gray matter of the olive forms a hollow shell with a wrinkled wall (Fig. 35). In the model it is made nearly solid inasmuch as, with the magnification used, its walls made strips of wax too thin to handle. It presents for examination six surfaces dorsolateral, lateral, ventral, proximal, distal and medial the last surface including the hilus. The dorsolateral surface, as its name indicates, slopes toward the lateral surface and passes over into it by a gradual curve. On the other hand, the ventral surface is practically level, but likewise rounds onto the lateral surface. This corresponds to the familiar form of the olive in cross-section (Fig. 35).
In Plate i, Fig. 1, is shown a lateral view, including the dorsolateral surface. The general outline of this view is of interest. The dorsal border is practically level. Starting from the distal end of the nucleus, the outline passes ventralward and forward by a gradual curve which reaches its most ventral point at the proximal end of the ventral surface. This will be recognized as the curve of the olive seen on the uncut medulla. The proximal border is slightly curved and represents the edge that faces the pons.
The surface of the olive is marked by deep sulci and more shallow grooves, so that the whole suggests the surface of a brain. From the view of the lateral surface it will be noted that all of these grooves run in an approximately dorsoventral direction.
The dorsal or dorsolateral surface shows three sulci. They are approximately parallel and divide the dorsal part of the olive into four lobes. These sulci are distinguishable from the other grooves on this surface in being deeper, for they reach down to the opening of the hilus, as can be seen in Fig. 19. The sulci do not pass over onto the curve of the lateral surface, which is marked by comparatively shallow grooves that more or less alternate with the deep sulci of the dorsolateral surface. From this fact it follows that the lobes are well marked only in the dorsal portion. It is evident that transverse sections of the olive would be all comparatively similar over the lateral curve, but would differ on the dorsolateral surface, according as the section passed through a sulcus or a lobe. This will be clear by comparing Figs. 31 and 32.
Of the four lobes, the first or proximal is the largest (Plate i, Fig. 1, L. p.). It is subdivided in the dorsal portion by two or three fairly deep grooves. The first sulcus runs a little obliquely, the dorsal end being further spinalward than the ventral. The first lobe has three surfaces (1) a dorsolateral, (2) a proximal and (3) a mesial. In other words, the first lobe curves around the proximal end of the nucleus to the mesial surface, so as to enclose a portion of the hilus. This explains why a cross-section of the proximal lobe shows the gray matter as a complete ring (Fig. 36). The first lobe is made up of three convolutions, or gyri, two of which are seen from the lateral view and the other from the mesial.
The second and third lobes consist each of a single convolution, or gyrus. They present but one surface, directed dorsolaterally. At the dorsal border they are comparatively narrow, but broaden out in joining the lateral surface.
The fourth lobe forms the distal end of the olive and is the smallest of all, consisting, like the second and third, of a single convolution or gyms. It does not curve around the hilus as does the first lobe (Fig. 20). Nevertheless, the lobe is placed obliquely, so that a cross-section of the extreme distal part is a small closed ring, the same as the cross-section of the proximal lobe.
The surface of the lobes and the sides of the sulci are marked by small grooves which run in a dorsoventral direction. Indeed, in the depth of the sulci are small folds in the nuclear wall. These can be seen in longitudinal section (Fig. 19).
The lateral surface forms the curve of the shell. Its dorsal margin (Plate i, Fig. 1) is an indistinct line where it curves onto the dorsolateral surface. Its ventral border makes the curve of the surface form. This curve or ventral border is so placed that the distal part of the lateral surface is narrow, that is, the part opposite the fourth lobe. The greatest breadth of the lateral surface is at the proximal end. The entire surface is covered by shallow grooves, of which the deepest alternates with the first and second sulci. It is worthy of note that all of the grooves of this surface run in a dorsolateral direction, as do those of the dorsolateral surface.
The ventral surface is smaller than the dorsal (Plate i, Fig. 2). It is for the most part horizontal, but at the spinal end it passes by a gradual curve onto the distal surface (Fig. 33). In its surface markings it contrasts with the dorsolateral and lateral surfaces, for instead of taking a dorsoventral direction, its grooves all radiate out from a point in the ventral border of the hilus (Plate i, Fig. 2). This point is opposite the word mesial in the figure. Thus it happens that while the distal groove runs transversely, as do those of the dorsolateral surface, the proximal groove runs longitudinally parallel to the raphe and at right angles to the grooves of the dorsolateral surface.
The grooves of the ventral surface are not marked by secondary furrows, as are the sulci of the dorsolateral surface. As has been said, these grooves appear to radiate from a point about the middle of the ventral border of the hilus. The first or most medial of these grooves (S. p.) runs directly parallel to the long axis of the olive, that is, in an anteroposterior direction. It is a deep groove and extends far dorsalward on the median surface, separating off a small gyrus from the main lobe. This is seen only on a view of the mesial surface which, unfortunately, is not given. The second (S. s.) passes obliquely toward the cerebrum and becomes continuous with one of the grooves of the lateral surface. The third (S. t.) lies still more obliquely and does not leave the ventral surface. The distal part of the ventral surface is somewhat damaged, inasmuch as the sections were here a little too much decolorized in preparation, but enough can be made out to say that the grooves run transversely and are the continuation of the grooves of the lateral surface.
The medial surface is not given in the plates. It shows the hilus. From this aspect it can be seen that the ventral part of the olive makes a floor for the hilus and the dorsal part, a roof (Fig. 33). The proximal end of the hilus is closed in by the first lobe (Fig. 20). Opposite each lobe of the surface is a deep groove in the cavity to which the hilus leads, and the sides of these main grooves are marked again by grooves which correspond each to one convolution of the external surface. In brief, the essential points of the form of the olive are (1) its general shape as a hollow shell, (2) its hilus, (3) its transverse grooves on the dorsolateral surface, and (4) its radiating grooves on the ventral surface.
The olives of both sides were modelled in the effort to see if the fissures above described offered a basis of symmetry. The symmetry proved to be sufficiently apparent to lead one to an emphasis of the differences. The three deep fissures of the external surface, as well as the three radiating grooves of the ventral aspect, corresponded in the two lines. The differences consisted in the relative size of two of the lobes. The first lobe of the right olive was larger than the corresponding lobe of the other side, while the fourth lobe of the right side was proportionately smaller. The term proportionately is accurate, inasmuch as the two olives are of the same length and the second and third lobes correspond in size on the two sides. The symmetry of the two olives is shown in Fig. 19. At this level the fourth lobe of the right side is but a single fold in the nuclear wall.
It is now necessary to relate the appearance of the sections to the Inferior olive form of the olive in the model. A typical cross-section, so to speak, in sections, shows the thin folded wall and the open hilus (Fig 1 . 33). Attention has already been called to the fact that the form of the wall varies according as a section passes through a sulcus or a lobe (Figs. 32 and 33). It will be noticed that, inasmuch as the sulci run slightly obliquely, no one section passes through the entire length of one sulcus. The sulci can be used in determining the symmetry of an olive cut in crosssection. In tracing the olive of the cross series of the same stage, it is found that the first lobe of one side is larger and the fourth smaller than the corresponding lobes of the other side, the same peculiarity that has been noted in the model. I have, however, no method of determining right and left side of either series as compared with a real medulla.
Sections in a longitudinal direction differ widely from those of the transverse series; they illustrate the symmetry of the olive, that is they show the relation of the lobes and sulci and the varying depth of the sulci and grooves far better than the transverse series (Figs. 16 to 23). The first section shows the dorsal border of the olive. In the next three sections the symmetry can be traced, and note made of the relative size of the first and fourth lobes. The relation of the wall of these two lobes to cross-sections is evident, that is, the obliquity of the fourth lobe and the curve of the wall of the first account for the closed circles at either end in the transverse series. The last three sections pass through the ventral wall and the direction of the sulci is the point of special interest.
In the various longitudinal sections it will be noted that there are groups of cells either as rings or as irregular figures, that are wholly separate from the main wall; some of these lie within and some without the hilus (Fig. 19). These can be understood by reference to the transverse series. If, for example, in Fig. 33, a transverse line is drawn across the dorsal wall of the olive, it will cut off rings of cells, and these rings will be of two types: (1) a ring from a fold that projects on the lateral surface, and (2) a ring from a fold that projects into the hilus. The rings of the first type lie without the hilus and have their outer margin corresponding to the surface of the olive; the rings of the second type lie within the hilus and have their inner margin corresponding to the surface of the olive. This is a practical point in modeling the olive.
Fibres of From this study of the sections it is clear that the fibres of the olive inferior olive. are non-medullated at birth and hence are not in the model.
Median Nucleus olivaris accessorius medialis. The medial accessory ' olive is an irregular nucleus, much broken by bands of fibres running through it. It lies opposite the main olive, between the interolivary layer of the lemniscus and the root-bundle of the !N". hypoglossus (Plate v). Its inferior limit extends farther spinalward than the nucleus olivaris inferior, but its proximal does not reach as far cerebralward. From the view of the lateral surface (Fig. 2), it consists of. three columns of cells running in a dorsoventral direction. Each of the columns has small separate masses of cells opposite its dorsal border. The first or distal column is by far the largest. Its ventral portion is thick and a prominent process from the distal ventral angle curves around the distal border of the N". hypoglossus and the main olive (Plate vn). It makes an indentation in the ventral part of the medulla sheet (Plate YI). At the proximal ventral angle the first column connects with the second. The dorsal border of the first column shows a spur of cells from the distal half, while corresponding to the proximal half is a small separate group of cells. The spur corresponds to the second indentation on the medulla sheet (Plate vi). The second column is thin and flat; opposite its dorsal border are two small masses of cells. The third column is about one-third as broad as the others; it makes a narrow column of cells, opposite the dorsal end of which is still another small nucleus.
FIG. 2. Diagram of Nucleus olivaris accessorius medialis.
In longitudinal sections these relations are clear. Fig". 20 passes Median through the three columns near the ventral border. The first, which is accessory olive clearly the largest, appears curving around the inferior border of the main olive. The root-fibres of the N. hypoglossus cut through it. The second and third columns need only be mentioned. Passing dorsalward, we have the three columns, making groups of cells between the fibres of the N. hypoglossus and the stratum interolivare lemnisci (Fig. 19). Fig. 17 shows the scattered groups of cells of the medial-accessory olive. Cross-section. In Fig. 29, is seen the ventral part of the first column. This is, however, much better developed in Figs. 30 and 31. In Fig. 32 the second column is present, while in Figs. 33 and 35 the third column is seen.
The nucleus olivaris accessorius dorsalis is not shown in the model, but Fig. 15 skows its shape. It varies in shape on the two sides. The distal portion lies dorsal to the third lobe of the nucleus olivaris inferior, and the proximal portion corresponds to the second lobe.
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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, February 17) Embryology Book - An Atlas of the Medulla and Midbrain 7. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_An_Atlas_of_the_Medulla_and_Midbrain_7
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