Paper - A note concerning the model of the medulla, pons and midbrain of a new-born babe as reproduced by Herr F. Ziegler (1903)
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|Florence Sabin describes midbrain development using human models from the Ziegler_Model Collection.
Modern Notes: midbrain |
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A Note concerning the Model of the Medulla, Pons and Midbrain of a New-born Babe as Reproduced by Herr F. Ziegler
By Florence R. Sabin, M.D. (From the Anatomical Laboratory, Johns Hopkins University.)
With 2 Figures. The model described in this note was made in the Anatomical Laboratory of the Johns Hopkins University. It has already been published and illustrated i).
1) Contributions to the Science of Medicine dedicated by his Pupils to William Henry Welch upon the Twenty-fifth Anniversary of his Doctorate and in Vol. IX of the Johns Hopkins Hospital Reports. Later it was republished as an Atlas by Friedenwald and Company of Baltimore.
At the suggestion of Professor Stöhr in Würzburg, Herr Ziegler (Atelier für wissenschaftliche Plastik) in Freiburg i. B., has undertaken to reproduce the model) in order that it may be put into the hands of those especially interested in the study of the nervous system.
1) A special circular in regard to the model can be procured from Herr Ziegler's Atelier in Freiburg i. B.
Whereas the original model included only one side of the region, the reproduction consists of four separate models each of which shows both sides. This is necessary in order that the different fibre bundles can be traced through their decussations. Owing to the complexity of the model it seemed wiser for me to go to Freiburg and personally direct the work; and indeed it has taken the entire cum mer to be sure not only that all of the details of the original model are accurately reproduced but also that the course of each path has been made clear for the student. As has been said the model as made by Herr Ziegler consists of four separate models. The first is a series of sections swung in a frame, to be used to relate the other models to transverse sections. The other three models represent the internal structures in plastic form. Each one is swung in a frame, which can be revolved to any degree (Fig. 1). Thus the models can be viewed from every aspect and each structure is brought to view without taking any thing apart. This seemed the wiser plan for in the first place it prevents the confusion the student would find in putting together so complex a structure and in the second place it avoids the breakage involved in frequent handling.
The models have been colored as in the original plates. All of the nuclei are in solid colors while the fibres are marked by lines upon a white back ground. In general, red is used as the color for motor structures and blue for sensory. The nuclei of the motor cerebral nerves as well as the ventral horns of the cord are in red and the motor root fibres are marked with red lines. On the other hand the nuclei of reception of the sensory cerebral nerves together with the dorsal horns of the cord and the nuclei of the dorsal columns, nuclei funiculi gracilis et cuneati are in blue. The sensory cerebral nerves are also marked with blue lines. All other fibres are marked with black lines and all other nuclei are in yellow.
As has been said, the first model is a series of sections. The second shows the surface form on the one side, and the structures just beneath the surface on the other. It corresponds to Plates I and II in the Atlas. The third model is designed to show the motor cerebral nuclei and nerves on the one side and the sensory on the other as in Plates III and IV of the Atlas. It relates the gray matter of the cord to that of the medulla. The fourth shows the deeper structures which make the foundation as frame work, namely the medial and lateral lemnisci, the corpus trapezoideum, and the fasciculus longitudinalis medialis. It relates the white matter of the cord to that of the medulla.
In as much as the model was made from the brain of a new-born babe, some of the fibre tracts are not yet medullated. The most important of these are the pyramids and the brachium pontis. These two structures lie near the surface, however, and are easily shown schematically. The course of the pyramidal tract is shown by heavy wires on models II and IV, while the position of the brachium pontis is indicated on model II.
The first model consists of six sections, so mounted as to correspond in position with models II — IV. The outlines of this sections are drawn on model II.
The drawings of the sections correspond with a series of sections shown in Koelltker, Handbuch der Gewebelehre des Menschen, Bd. 2, 1896, for he pictures sections of about the same stage as the model cut perpendicularly to the long axis.
The first section represents the spinal cord above the cervical swelling. The second passes through the decussatio lemniscorum and is a little farther cerebralward than Koelliker's Fig. 443. The third is a typical section of the medulla and corresponds with Fig. 466 except that the nucleus funiculi cuneati occupies the place of the radix descendens n. vestibuli. The fourth passes through the nucleus of the N. abducens and corresponds with Fig. 490, while the fifth passes through the upper part of the pons just spinalward from the N. trochlearis. It is to be compared with Fig. 559. The sixth section passes through the midbrain at the level of the superior colliculus as shown in Fig. 567. Koelliker has two more figures, namely 560 and 561, which pass through the inferior colliculus and show, as does the model, that at birth the inferior colliculus lies opposite the peduncle rather than opposite the pons as in the adult. That is to say, the growth of the pons is forward or cerebralward.
The second model shows the surface form on the right side, and the structures just beneath the surface on the left (Fig. 1). The transverse lines represent the position of the sections of model I. The lower end of the model is the same as the first section of model I, and represents the spinal cord. The relations of the dorsal funiculi to their nuclei as well as the origin of the corpus restiforme from the dorsal funiculi and the fasciculus cerebrellospinalis are clearly shown.
This model also shows the relation of the three cerebellar peduncles to each other. The middle peduncle, or brachium pontis is nonmedullated and shows as a narrow band on the surface form on the right hand side. The superior and inferior peduncles have been prolonged slighthy free hand by the aid of transverse sections in order to show their relative positions as they enter the cerebellum. The superior peduncle or brachium conjunctivum passes obliquely dorsalward to the corpus dentatum, the anterior, ventral tip of which is shown in outline. — The inferior peduncle or corpus restiforme passes dorsalward just lateral to the anterior tip of the corpus dentatum and to the brachium conjunctivum.
Certain of the relations in the midbrain are also clearer in this model than in any other. For example the position of the lemniscus medialis with regard to the pyramidal tract, the red nucleus and the substantia nigra.
The third model is designed to show the cerebral nerves and the relation of their nuclei both to each other and to the gray matter of the cord. Beginning with the lower end of the model, the dorsal and lateral columns of the spinal cord have been removed so that the gray matter is exposed. The dorsal horns are colored blue and the ventral red. The motor nuclei are represented on the left hand side and the sensory on the right.
Just at the junction of the cord with the medulla, the ventral horn, which is split off from the rest of the gray matter by the decussating pyramidal fibres, divides into two parts, a medial and a lateral. The medial division gives rise to the nuclei of the hypoglossus, abducens, trochlearis and oculomotorious nerves, while the lateral division gives rise to the motor nuclei of the spinal accessorius, vagus, glossopharyngeus, facialis and trigeminus nerves. Two wires from the ventral horn show this division and represent the scattered cells that connect the ventral horn with the nucleus n. hypoglossi medially, and with the nucleus ambiguous laterally.
The contrast between these two groups of nerves is well brought out. The nuclei of the median group lie in the floor of the ventriculus quartus or aqueductus Silvius, along the course of the fasciculus longitudinalis medialis. The root fibres all pass directly ventralward and emerge near the median ventral line, except these of the N. trochlearis which pass dorsal ward, decussate in the velum and emerge near the dorsal median line. On the other hand the lateral group of nuclei lie farther ventralward and the root fibres of all except these of the N. trigeminus make an arch in passing outward. That is to say the fibres pass first inward and dorsalward and then turn veutralward and outward to emerge in the lateral line.
On the right hand side of the model are shown the sensory cerebral nuclei. The nuclei funiculi gracilis et cuneati, which lie in the path of the dorsal fasciculi represent the sensory nerves of the spinal cord. The posterior horn as it is in the cord is shown in the cross section ; in entering the medulla, the horn or the substantia gelatinosa Rolandi swells and becomes the nucleus of the N. trigeminus. This nucleus extends as far as the pons where the root bundle of the nerve enters. The fibres of the root bundle divide into short ascending branches which enter the anterior end of the nucleus, and into long descending branches making the tractus spinalis n. trigemini which extends along the lateral border of the nucleus as far as the spinal cord.
The sensory parts of the glossopharyngeus and vagus nerves are clearly shown as well as their relation to the motor part. The sensory fibres take two separate paths. First a definite compact bundle passes inward and dorsalward just lateral to the tractus spinalis n. trigemini and turns spinalward to make the tractus solitarius. Second, scattered fibres pass through the tractus spinalis n. trigemini and enter the ala cinerea. With these scattered fibres run the motor fibres of the same nerves, as represented in the model by red wires.
A part of the nucleus n. vestibuli medialis and the corresponding fibres have been cut away to show the deeper structures, but by comparing with modell II the entire nerve is made plain. Similar to the N. trigeminus, the root bundle passes inward and dorsalward, and then the fibres divide into ascending and descending branches. The nucleus is also a continuous mass of cells lying just internal to the tracts. The cells opposite the radix descendens n. vestibuli make the nucleus n. vestibuli medialis while those opposite the ascending branches make the nucleus n. vestibuli superior or Bechterew's nucleus. Where the fibres of the vestibular root bundle divide is a third nucleus, the nucleus n. vestibuli lateralis or Deiters' nucleus whose fibres pass to the spinal cord. This path is to be seen in model IV. The nucleus has been colored yellow (red in the atlas), because its cells do not correspond strictly in type either to these of a sensory or a motor nerve. The vestibular fibres which enter the cerebellum are shown by wires on models II and III. The commissure between the two nuclei n. vestibuli superiores is shown in model III in connection with the brachium conjunctivum.
This third model brings out the similarity between the sensory paths. Each sensory nerve on entering divides into a long descending tract and a short ascending one. There are however no ascending fibres shown for the glossopharyngeus and vagus nerves. The sensory nuclei, which are derived from the dorsal horn accompany these tracts throughout their length and lie just internal to them. From all of these nuclei pass internal arcuate fibres into the lemniscus medialis. The vestibular nerve is peculiar in its relations to the cerebellum. The cochlear nerve is not to be horaologized with the other sensory nerves, either in the position of its nucleus or in the course of its fibres. Its path is wholly ascending and is best seen in model IV, where the corpus trapezoid eum is more uncovered.
Besides the cerebral nerves, this model shows certain relations in the midbrain, and the difi'erent areas in the formatio reticularis better than the others. In the midbrain the form of the stratum profundum album is prominent. Farther ventral lies the red nucleus embedded in its capsule. Passing from the nucleus are the fibres of the brachium conjunctivum, the decussation of which is best seen from the ventral aspect. The fibres as they enter the cerebellum are however to be seen from the lateral and dorsal aspects.
The position of the areas of the formatio reticularis can be seen in this model. In the cord the area is small and limited to the angle between the two horns. In the medulla the area is wide and lies dorsal to the olive and lateral to the fibres of the fasciculus longitudinalis medialis. In the pons the area is dorsal to the lemniscus medialis while in the midbrain it is internal to the lemniscus and dorsal to the nucleus ruber. In the medulla the fibres which lie between the lemniscus medialis and the fasciculus longitudinalis medialis belong also to the formatio reticularis. In the course of this path lies the nucleus centralis inferior just spinalward from the N. abducens. In entering the pons these fibre bands broaden out and enclose on either side the nucleus reticularis tegmenti. Farther cerebralward in the course of these fibres lies the great mass of cells called the nucleus centralis superior; the pars medialis of which lies in the central line, while the pars lateralis occupies the hollow of the brachium conjunctivum. These relations can be seen in Fig. 13 in the Atlas.
The fourth model is to show chiefly the lemniscus medialis and its connections (Fig. 2). Whereas the third model shows the relation of the gray matter of the cord to the gray matter of the brain stem, the fourth shows the relation of the white matter or fibre bundles of the cord to those of the brain stem. To that end the gray matter of the cord has been removed from the cross section of the lower end.
The dorsal columns of the cord are clearly shown in the cross section and then a portion of the fibre bundles have been cut away in order to uncover the corresponding nuclei. The connection between the fibre bundles of the dorsal columns and their nuclei is made by wires which show that the fibres take four paths in entering the medulla. 1) The fibres of the fasciculus gracilis enter the nucleus funiculi gracilis. From here a new set of fibres passes across the median line as the decussatio lemniscorum and enters the lemniscus medialis of the opposite side. 2) One bundle of fibres from the fasciculus cuneatus enters the nucleus funiculi cuneati lateralis (Blumenau) while fibres enter the corpus restiforme. The fibres which pass directly from the dorsal funiculi to the corpus restiforme are shown on model II. 3) Another group of fibres from the fasciculus cuneatus enters the nucleus funiculi cuneati from whence a new set of fibres pass as fibrae internae arcuatae across the middle fine and enter the lemniscus mediaHs. 4) A set of fibres from the dorsal funiculi enters the formatio reticularis region of the medulla.
The fasciculi laterales can be traced in the same way. 1) The fasciculus cerebello- spinalis is clearly shown on the right hand side as it enters the medulla, turns dorsalward and passes into the corpus restiforme. 2) The fasciculus lateralis proprius can be separated at this stage into three parts which are shown by wires on the right hand side. The first bundle turns inward as it enters the medulla and probably joins the medial lemniscus. The second passes from the nucleus n. vestibuli lateralis (Deiters) to the spinal cord. The third runs from the cord as far as the corpus trapezoideum. 3) The crossed pyramidal tract is shown by heavy wires. The wires indicating the position of the pyramidal tract for the entire model show best on the ventral surface.
The ventral columns of the cord consist first of the direct pyramidal fibres which show best on the ventral surface of the fourth model. The rest of the ventral column fibres show best on the left side of the model or from its dorsal aspect. For the most part they enter the fasciculus longitudinalis medialis.
The shape of the lemniscus medialis has been emphasized in my previous paper; the perpendicular sheet in the medulla, the horizontal one in the pons and the lateral oblique sheet in the midbrain. The course of the fibres of the fasciculus longitudinalis medialis has been made plain by lines and wires. The descending fibres start from the superior colliculus and pass through the commissura posterior to the nucleus fasciculi longitudinalis medialis (Dakkschewitsch). From there fibres enter the tract. The ascending fibres from the ventral column of the cord have already been mentioned.
The complete course of the cochlear path is to be seen also on model IV. From the nucleus n. cochleae ventralis fibres pass beneath the corpus restiforme as the corpus trapezoideum to the nucleus olivaris superior of the opposite side, while from the nucleus n" cochleae dorsalis fibres pass over the corpus restiforme as the striae acusticae to the same nucleus. From the nucleus olivaris superior fibres pass in the lemniscus lateralis to the nucleus colliculi inferioris.
Cite this page: Hill, M.A. (2021, April 20) Embryology Paper - A note concerning the model of the medulla, pons and midbrain of a new-born babe as reproduced by Herr F. Ziegler (1903). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_A_note_concerning_the_model_of_the_medulla,_pons_and_midbrain_of_a_new-born_babe_as_reproduced_by_Herr_F._Ziegler_(1903)
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