Book - An Atlas of the Medulla and Midbrain 1
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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 I. Introductory
The method of studying structures by means of accurate reconstructions made from wax plates was introduced by Born. This method has already been used by many observers in the fields of embryology and comparative anatomy, but, as far as I am aware, no one, except His, has employed it in the study of the central nervous system. The models of His represent the development of the external form of the neural tube and the positions of the cerebral nerves. In the present work, the representation of external form has been wholly secondary, the aim having been to show the form of the internal structures, namely, of the nuclei, the nerves and the central tracts. The great work of His must form the basis of any study dealing with the development of the nervous system, and the conclusions of this paper are, in the main, in accord with his views. The model constructed by Edinger, which has been of marked help to teachers and students of neurology, gives the general position of the different structures, but does not attempt to illustrate their form. 1
Material. The model was made from a series of horizontal sections passing through the medulla, pons and midbrain of a newborn babe. It is an example of the embryological method of studying the nervous system, that is, the method of successive myelenization of paths as distinguished from that of degeneration, or from the experimental method. A second set of sections cut transversely, and representing almost the same stage of medullation, has been used as a check upon each point of the model. The specimens were prepared by Dr. John Hewetson in the Anatomical Laboratory of the University of Leipzig. The material was preserved in Miiller's fluid and the sections stained by the Weigert-Pal method. The sections were cut at 70 //. Each brain was made to give two separate series by mounting alternate sections; therefore, in building the model, each section represents two, or 140 /*, instead of 70. The material was embedded in celloidin. The sections were numbered serially and care was taken not to invert any of them. No record was made, however, of the right and left sides of the original medulla. For building the model, the horizontal series was preferable to the transverse; first, because the sections were larger and fewer (108 instead of 221); and secondly, because there was less danger of distortion, for a majority of the fibre-bundles of the model run longitudinally, and hence it often happens that the entire course of a bundle may be seen in one longitudinal section while the same bundle may extend through from 50 to 60 of the transverse series.
1 Edinger, L. Model! des oberen Ruckenmarksteiles and der Oblongata. Anat. Anz., Jena, Bd. vin, 1893, S. 172-175.
Building Method. The method of Born for making wax models from serial sections is as follows : It is necessary (1) to have an accurate drawing of each section magnified to a certain degree, (2) to transfer the drawing to a wax plate (care being taken to magnify the thickness of the section in the same proportion as the length and breadth), (3) to cut each structure from the plates, (4) to pile each so as to show its own form and its relations to all other structures and (5) to fuse the pieces of each structure into a unit. The magnification decided upon, namely, 14.5, was merely one of convenience; in the first place it gave a wax plate of 2 mm. thickness, which was easy to work with, and, secondly, made a model of convenient size.
To make the drawings, it is the custom of the laboratory to use a Zeiss projection apparatus and electric lamp. The light passes through a condenser and lens and the image is received on a movable though firm screen. In adjusting the apparatus certain points are to be noted: (1) the screen and the slide upon which the section is mounted must be kept parallel to each other and perpendicular to the ray of light passing the centre of the section; (2) each section must be placed in the same relative position to the light and screen in order that none of the drawings be reversed; (3) it is necessary to focus for the centre of the section and to test the magnification each time the apparatus is used; (4) the micrometer slide used for this test must be placed with the ruled side next the coverslip to bring the lines and section into focus at the same time; (5) the checking must be done on the paper which is to receive the drawings.
The drawings thus obtained are merely outlines. In making them two points are essential accuracy and definiteness. This is easy to accomplish in the case of a bundle of black fibres placed against a light background, but many of the structures are by nature indefinite. For example, it will be seen in Fig. 6 that the nuclei of the vestibular nerve fade gradually into the gray masses about the central canal. To limit the error as much as possible the following precautions were taken: (1) each section was studied with a dissecting microscope and a Leitz Obj. 3. before making the drawings, (2) each line of the drawings was controlled with the microscope, and (3) all of the masses outlined were measured and compared with the corresponding structures in the transverse series.
After clear and definite outline drawings had been obtained, an elaborate color system was devised, so that each structure in the series could be indicated by its own shade. Such a system is essential in reconstructing so complex a structure. After all controls had been made the drawings were transferred to the wax plates.
The wax plates are made in the anatomical laboratory in a large Making the pan 90 cm. wide by 120 cm. long. The mass employed consists of * ordinary beeswax mixed with 1/19 of its weight of resin. The melted wax is then poured through a strainer into a tarred receptacle on a balance, the weight of wax necessary for one plate of 2 mm. thickness being in turn poured into the large pan which is half-full of hot water. The wax spreads evenly over the surface of the water, any bubbles being removed by means of a strong gas flame. When the wax has solidified enough to be firm, yet not brittle, the plate is removed from the pan and laid on a level surface so that the edges will not curl. Every fifth plate is made black by mixing soot with the melted wax. This is of much help, for it is then easy to determine quickly the number of any plate in the model.
The drawings were transferred to the wax plates by means of carbon tracing paper, and were colored with oil paints. Each section was then cut from its plate. The cutting is made easy by placing the slightly warmed wax plate on a sheet of glass and following the outlines of the section with a thin, narrow-bladed knife. Each plate gives two parts, one corresponding to the section itself, and the other to the shell. These two parts, numbered to correspond, were placed in two separate piles. Since, unfortunately, no pictures of the original medulla from which the sections were cut were available, the parts corresponding to the sections were piled repeatedly until the external form of a babe's medulla was reproduced. The shells were then piled to correspond and a plaster cast of the cavity thus made gave the external form of the medulla to be modeled. On the plaster cast the markings corresponding to the edges of the individual wax plates were visible so that it was an efficient control for later work.
The base of Inasmuch as the whole of the ventral portion of the sections was made up of non-medullated fibres, this portion of the cast was duplicated and used as a pedestal upon which to support the model. This pedestal is of interest, inasmuch as it contains the pyramidal tract except at the extreme spinal end of the model. The position of the pyramidal tract can be imagined in connection with [[: ; starting at the cerebral end of the model, the tract lies first ventrolateral to the substantia nigra ; it then plunges into the pars basilaris pontis, and enters the ventral border of the medulla where its decussation can be related by the distal border of the olive.
chief plane of In building the model I made use of two main guides (1) the aTs f o r page 32)! external form and (2) the median longitudinal plane. By a study of the series it was found that, at a certain level, the medial lemniscus ran through the entire length of a section, and could be related, therefore, both to the external form and to the median plane. With this in view, the section No. 122, shown in Fig. 16, was chosen as a starting-point, and drawn upon the surface of a flat board. The median longitudinal axis of the section was drawn as a guide. From the wax plate corresponding to this section the medial lemniscus was cut and secured in position on the drawing on the board, thereby fixing its relations to the guiding lines, namely, the periphery and central axis. The medial lemniscus was then cut from each of the sections in series. To find the position of each successive piece of wax representing the medial lemniscus, it was necessary to determine the position of its plate. This was done by placing the plaster cast parallel with the section on the board and then examining the position of each plate on the cast with reference to the plate numbered 122. Measurements were made, especially from the ends of the sections, and the median plane was kept true. By this comparison a wax plate could be held in proper position with reference to the board; it was then easy, on holding the plate a little higher, to sight through the space made by the removal of the bundle representing the medial lemniscus and adjust the piece of wax corresponding to it into place below. The position of each piece was checked also by measurements from various points on the sections. In this preliminary reconstruction, which may well be called the foundation of the model, the trapezoid body was included, inasmuch as it forms a cross-bar and, therefore, gave many points for control measurements.
Before fusing the pieces of this foundation, I used as a further check upon the piling the external form of the inferior olive, which is so complex that its parts must be piled accurately in order to fit at all. Moreover, since the olive makes a definite curve on the surface of the medulla oblongata, the shells left after cutting out the nucleus were piled with reference to this curve; the nucleus in turn was piled by measurements from the shells. The olive thus modeled was placed in position with reference to the medial lemniscus, and it was found that measurements taken from various points on the olive to the lemniscus agreed with the corresponding measurements on the sections. This confirmed the conviction that the latter had been piled correctly. A further check of the accuracy of the work was found by comparing the dorsal border of the lemniscus in the model with the same border, as seen in a sagittal section of the medulla oblongata. Having made sure of the accuracy of the piling of the foundation, its parts were fused by means of a hot iron, strengthened by buried wires and fastened securely to the pedestal.
With the help of this foundation, all the structures of the model were piled. Each bundle was taken up separately, its parts cut from the plates, piled and fused into a unit. At the end, the entire model was found to fit, which was a further test of the accuracy of the work.
The value of such a model lies in its illustration of spatial relations and the suggestions which these give with regard to the course of the development. It is necessary to point out certain limitations of the method. First, in making the model, fibres were grouped together according to their function. The bundles thus made have very different values, some consisting of many fibres closely packed, others of few and scattered fibres. This is well illustrated in the case of the root of the N. f acialis, in which the though it contains the same number of fibres. The size of the bundle, then, is no indication of the number of the fibres, and such details must be studied on the sections themselves. Secondly, in several instances, a bundle of fibres passes directly through another bundle or through a nucleus. In such cases some sacrifice had to be made, but the rule has been to give enough of each bundle to show its direction and extent.
pars prima makes a much larger bundle than the pars secunda, 2
The treatment of the formatio reticularis deserves special mention. As has been said, in order to model a bundle, it must be possible to give it a definite outline. Though this was impossible in the case of the formatio reticularis, in building the model it became clear that the area as a whole was fairly definitely bounded by other structures and could, therefore, be represented as a space. Moreover, though most of the fibres of the formatio reticularis alba are diffusely distributed, some of them make fairly definite bundles for a part of their course. The gray matter, or formatio reticularis grisea, likewise has a few groups of cells definite enough to be represented by their boundaries.
It may be well to state at the outset wherein this work presents new features. It is believed that here, for the first time, the form relations of the fibre-bundles and gray masses of the pons and medulla oblongata are shown in three dimensions. Certain observers have given descriptions that permit most graphic mental pictures, but as far as I am aware no one has treated the subject as a whole from the point of view of form. In several instances weight has been added to previous discoveries by showing that they agree with the anatomical relations shown more clearly in the model than in sections. In the description of the model each point mentioned has been supported by both series of sections, and it may be well to state that no claim of originality is made in reference to determining the structures in the sections save in a few minor points which will receive especial mention.
Method of Using Atlas
The model as a whole will be most readily understood by comparing the surface views with pictures of the brain in text-books. For example, compare File:Sabin1901 plate02.jpgPlate II, the lateral view of the model, with the figures on page 54 of Van Gehuchten's Le Systeme Nerveux de L'Homme (edition 1900), and on pages 42 and 127 of Quain's Anatomy, Vol. in, Pt. i. The Spinal Cord and Brain (Longmans, Green & Co., 1895). These figures are of the adult brain, and it will be noted that in them both the clava and the midbrain are relatively less prominent than in the model of the new-born baby's brain, the fibres of the pons being non-medullated at birth. The dorsal view of the model (Plate III), showing on the right side the floor of the fourth ventricle, on the left the structures beneath the floor, is to be compared with a similar view in Van Gehuchten's Anatomy, page 62, and in Quain's, page 48.
In studying the nervous system by means of sections, only imperfect ideas of the form of the different tracts can be obtained. A reconstruction, however, enables one to see an entire tract as a unit, after which its minute details can be studied. The plan of the present work is as follows : First, to call attention to each tract as it appears in cross-section, that is, to identify it; second, to describe the bundle in the reconstruction; third, to return to the sections and, using both series, to show how the points brought out in the model are shown in the sections. The illustrations show each tract both as a unit and cut in serial sections. The model and the sections should therefore be studied together. A sagittal series can also be used with the model.
Two sets of serial sections are given, one transverse and the other horizontal. These can be related to the model as follows: the Figure 52 represents an outline of the lateral view of the model, with scales on the margins representing the position of the sections of the two series. By joining opposite lines with a ruler or drawing similar parallel lines any section can be located. The lines for the horizontal series must curve slightly to allow for the perspective of the drawing. By comparing Fig. 52 with other pictures of the model, sections can be related to each plate.
Though, as has been said, a complex color system was necessary in building the model, in presenting it as a finished structure the color system color system has been made simple. All the fibres are shown in white and black, the nuclei of the gray substance in colors. Of these but three have been used red for the motor nuclei, blue for the sensory and yellow for all other nuclei. In describing the model, the words proximal and distal have been used, proximal meaning toward the cerebrum, and distal away from it.
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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. (2021, April 10) Embryology Book - An Atlas of the Medulla and Midbrain 1. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_An_Atlas_of_the_Medulla_and_Midbrain_1
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