Difference between revisions of "Paper - On the development of the nuclei pontis during the second and third months of embryonic life (1901)"

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[[Carnegie Collection]]: {{CE45}}, {{CE75}}, {{CE86}}, {{CE95}}
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{{Historic Disclaimer}}
=On the development of the nuclei pontis during the second and third months of embryonic life=
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=On the Development of the Nuclei Pontis during the Second and Third months of Embryonic Life=
  
 
By Margaret Long.
 
By Margaret Long.
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[From the Anatomical Laboratory of Johna Hopkins Vnu'erxitij.)
 
[From the Anatomical Laboratory of Johna Hopkins Vnu'erxitij.)
  
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This work was undertaken in the fall of 1899 at the suggestion of Doctor Barker, and has been carried out with his assistance. The specimens used are human embryos and were very kindly lent by Doctor Mall from his collection.
  
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* The numbers of the embryos correspond with their numbers in the embryological cabinet of the Anatomical Laboratory of the Johns Hopkins University.
  
This work was undertaken in the fall of 1899 at the suggestion of Doctor Barker, and has been carried out with his assistance. The specimens used are human embryos and were very kindly lent by Doctor Mall from bis collection.'
 
 
' The numbers of the embryos correspond with their numbers in the embryological cabinet of the Anatomical Laboratory of tlie .lohns Hopliins University.
 
  
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The following embryos are described in the order of their probable age, as estimated by their length and by the develojiment in the rhombencepbalon. The arrangement of the cerebral nerves and the general appearance of the {{medulla oblongata}} agree with the His models and with the description given by His in "''Die Entwicklung des menscblicben Kautenhirns''"; a description of these is accordingly unnecessary. Each embryo has been studied in serial sections and from tliese sections a few, at different stages of development,. have been selected as characteristic of the structure of the pons, its nuclei and fibres. To make the work complete it will be necessary to study more embryos at intermediate stages between the five given here, and others from the third montli up to the adult pons.
  
  
The following emljryos are described in the order of their probable age, as estimated by their length and by the develojiment in the rhombencepbalon. The arrangement of the cerebral nerves and the general appearance of the medulla oblongata agree with the His models and with the description given l)y His in "Die Entwicklung des menscblicben Kautenhirns"; a description of these is accordingly unnecessary. Each embryo has been studied in serial sections and from tliese sections a few, at different stages of development,. have been selected as characteristic of the structure of the pons, its nuclei and fibres. To make the work complete it will be necessary to study more embryos at intermediate stages between the five given here, and others from the third montli up to the adult pons.
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Embryo No. LXXV {{{CE75}}} is 30 mm. long and has been cut into serial sagittal sections. The nuclei, whiuli I have designated as " B," " C," " D," " E " and " H " in the various sections, are masses of cells distributed through the ventral part of the mantle layer (Mantelsehicht of His) at or near the level of the pontal flexure. The most medial of these nuclei extend to within 0.7 mm. of the middle line. An unstained fibre bundle can he .seen on the surface of the rhombencephalon ventral to the mantle layer throughout its entire length.
  
Embryo No. LXXV is 30 mm. long and has been cut into serial sagittal sections. The nuclei, whiuli I have designated as " B," " C," " D," " E " and " H " in the various sections, are masses of cells distributed through the ventral part of the mantle layer (Mantelsehicht of His) at or near the level of the pontal flexure. The most medial of these nuclei extend to within 0.7 mm. of the middle line. An unstained fibre bundle can he .seen on the surface of the rhombencephalon ventral to the mantle layer throughout its entire lengtli.
 
  
 
Section No. 73 is 2.1 mm. to the left of the middle line (Fig. 1). Near the ventral surface on the cerebral side o.f the nervus trigeminus is a well defined cell-mass, '" B.' On the ventral surface opposite the nervus acusticus is a deeply stained cell-mass, " IT," which (wlien followed in the series) is seen to extend lateralward and spinalward to the floor of the fourth ventricle at the Junction of the latter with the telachorioidea. The section of the mantle layer presents longitudinal striations which have a slight ventral convexity. A few of these strands are more deeply stained than th.e rest between the level of the N. trigeminus and that of the N. acusticus. The dark ependymal epithelium and the unstained ventral fibre bundle are evident.
 
Section No. 73 is 2.1 mm. to the left of the middle line (Fig. 1). Near the ventral surface on the cerebral side o.f the nervus trigeminus is a well defined cell-mass, '" B.' On the ventral surface opposite the nervus acusticus is a deeply stained cell-mass, " IT," which (wlien followed in the series) is seen to extend lateralward and spinalward to the floor of the fourth ventricle at the Junction of the latter with the telachorioidea. The section of the mantle layer presents longitudinal striations which have a slight ventral convexity. A few of these strands are more deeply stained than th.e rest between the level of the N. trigeminus and that of the N. acusticus. The dark ependymal epithelium and the unstained ventral fibre bundle are evident.
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Section No. 96 is 1.05 mm. to the left of the middle line. "H" and "C" are still present. The ventral fibre bimdle passes partly along the dorsal surface of "H" and partly between " C " and " E." Just cerebralward from the pontal flexure, close to the floor of the ventricle, is " M, an oval mass of cells witli a clear unstained area behind at its spinal end, and measuring 0.8 mm. in transverse diameter. The appearance of the mantle layer is the same as before. In its dorsal and cerebral part is seen an unstained dorsal fibre bundle.
 
Section No. 96 is 1.05 mm. to the left of the middle line. "H" and "C" are still present. The ventral fibre bimdle passes partly along the dorsal surface of "H" and partly between " C " and " E." Just cerebralward from the pontal flexure, close to the floor of the ventricle, is " M, an oval mass of cells witli a clear unstained area behind at its spinal end, and measuring 0.8 mm. in transverse diameter. The appearance of the mantle layer is the same as before. In its dorsal and cerebral part is seen an unstained dorsal fibre bundle.
  
Embryo No. LXXXVI is 30 mm. long and has been cut into serial coronal sections. There is ventralward a definite mass which I have designated as the nucleus pontis ventralis; it is about 1 mm. long by 3 mm. wide. The raphe enters
 
  
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Embryo No. LXXXVI ({{CE86}}) is 30 mm. long and has been cut into serial coronal sections. There is ventralward a definite mass which I have designated as the nucleus pontis ventralis; it is about 1 mm. long by 3 mm. wide. The raphe enters this nucleus in the middle line. Dorsal from its lateral part are several scattered masses which 1 have designated, tentatively, the nuclei pontis dorsales. The unstained ventral fibre bundle is dorsal from the nucleus pontis ventralis.
  
  
this nucleus in the middle line. Dorsal from its lateral part are several scattered masses which 1 have designated, tentatively, the nuclei pontis dorsales. The unstained ventral fibre bundle is dorsal from the nucleus pontis ventralis.
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Section No. 175 is spinalward from the masses mentioned. On the ventral surface medialward from the nervus acusticus (-A^.l ) is the cell-mass " H." Followed through the series this cell-mass extends spinalward, dorsalward and lateralward to the ependymal epithelium of the fourth ventricle; cerebralward, it is medial to the nervus trigeminus and continuous with the nucleus pontis. Taken in order from the raphe lateralward in the mantle layer are the nucleus olivaris superior (8) and the superior olivary complex {S}, the ascending and descending parts of the root of the nervus facialis, the nucleus nervi facialis {NNP), and the corpus restiforme {OR). On the floor of the fourth ventricle are the nucleus nervi abducentis (NNA) and the nucleus N. vestibuli (radicis deseendentis), {III? I'D); further lateralward are the nuclei N. cochleae, namely the nucleus N. eochleffi dorsnlis (NRCD) and the nucleus N. cochlea; ventralis (NNCV). The unstained area is the ventral fibre bundle (I'-P') Section No. 184 is 0.45 mm. cerebralward from the preceding section. In the mantle layer are seen in order the nucleus olivaris superior, (S), the nucleus nervi facialis (NNF). and parts of the ascending and descending limbs of the nervus facialis. "H" is on the ventral surface lateral from tlie nervus facialis. On the floor of the fourth ventricle is the nucleus N. vestibuli medialis et radicis descendentis (NNV).
  
Section No. 175 is spinalward from the masses mentioned. On the ventral surface medialward from the nervus acusticus (-A^.l ) is the cell-mass " H." Followed through the series this cell-mass extends spinalward, dorsalward and lateralward to the ependymal epitlu^lium of the fourth ventricle; cerebralward, it is medial to the nervus trigeminus and continuous with the nucleus pontis. Taken in order from the raphe lateralward in the mantle layer are the nucleus olivaris superior (8) and the superior olivary complex {S}, the ascending and descending parts of the root of the nervus facialis, the nucleus nervi facialis {NNP), and the corpus restiforme {OR). On the floor of the fourth ventricle are the nucleus nervi abducentis (NNA) and the nucleus N. vestibuli (radicis deseendentis), {III? I'D); further lateralward are the nuclei N. cochleae, namely the nucleus N. eochleffi dorsnlis (NRCD) and the nucleus N. cochlea; ventralis (NNCV). The unstained area is the ventral fibre bundle (I'-P') Section No. 184 is 0.45 mm. cerebralward from the preceding section. In the mantle layer are seen in order the nucleus olivaris superior, (S), the nucleus nervi facialis (NNF). and parts of the ascending and descending limbs of the nervus facialis. "H" is on the ventral surface lateral from tlie nervus facialis. On the floor of the fourth ventricle is the nucleus N. vestibuli medialis et radicis descendentis (NNV).
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Section No. 202 is 0.9 mm. cereliralward from section 184. The nucleus pontis ventralis reaches lateralward as far as the nervus trigeminus. In the middle line the raphe extends from the nucleus pontis to the ependymal epithelium. The nuclei pontis dorsales consist of several irregular masses, " A," " B," " C," and " E," and a more ventral and lateral mass. " D." These nuclei extend through the pons for a distance of 0.5 mm. in the cerebrospinal diameter. Between these ventral and dorsal nuclei is the unstained ventral fibre bundle. Lateral from the nervus trigeminus are the nucleus nervus trigeminus ascendcns and an unstained area.
  
Section No. 202 is 0.9 mm. cereliralward from section 184. The nucleus pontis ventralis reaches lateralward as far as the nervus trigeminus. In the middle line the raphe extends from the nucleus pontis to the ependymal epithelium. The nuclei pontis dorsales consist of several irregular masses, " A," " B," " C," and " E," and a more ventral and lateral mass. " D." These nuclei extend through the pons for a distance of 0.5 mm. in the cerebrospinal diameter. Between these ventral and dorsal nuclei is the unstained ventral fibre bundle. Lateral from the nervus trigeminus are the nucleus nervus trigeminus ascendcns and an unstained area.
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Embryo No. XLV ({{CE45}}) is 28 mm. long, and has been cut in serial sections, which divide the pons in an oblique direction in the following way: Instead of corresponding to the transverse diameter of the pons the left side of each section is further spinalward than the right side of the same section. The ventrodor.sal plane of the section is also oblique, so that in each section the left half of the dorsal surface is the more lateral, but in the right half of the pons the dorsal surface is more medial than the ventral. In other words, the first section removes a small portion of the pons about the cerebral ventral corner on the left side, and at the dorsal-spinnl angle on the right side.
  
Embryo No. XLV is 28 mm. long, and has been cut in serial sections, which divide the pons in an oblique direction in the following way: Instead of corresponding to the transverse diameter of the pons the left side of each section is further spinalward than the right side of the same section. The ventrodor.sal plane of the section is also oblique, so that in each section the left half of the dorsal surface is the more lateral, but in the right half of the pons the dorsal surface is more medial than the ventral. In other words, the first section removes a small portion of the pons about the cerebral ventral corner on the left side, and at the dorsal-spinnl angle on the right side.
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The nucleus pontis, as seen in this series, is on the surface of the rhombencephalon and follows the curve of the pontal flexure so that it is crescentic in shape, with a ventral convex surface and cerebral and spinal ends or horns. Consequently the following sections may have a ventrocerebral, a ventral, a veutrospinal and a dorsal edge.
  
The nucleus pontis, as seen in this series, is on the surface of the rhombencephalon and follows the curve of the pontal flexure so that it is crescentic in shape, with a ventral convex surface and cerebral and spinal ends or horns. Consequently.
 
  
  
 
PLATE XXI.
 
PLATE XXI.
  
Fig. 1. — Section through the pous of erabrj'o LXXV, oO mm. lous; X 1.5 diameters.
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Fig. 1. — Section through the {{pons}} of embryo LXXV, oO mm. lous; X 1.5 diameters.
  
  
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Fig. 4. — Section No. 17.5 tlirougli tlic brain of embryo LXXXVI, oO mm. long, x 15 diameters.
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Fig. 4. — Section No. 17.5 through the brain of embryo LXXXVI, oO mm. long, x 15 diameters.
  
  
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Fig. 5. — Sectiou No. 1.S4 throuirb embryo LXXXVI.
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Fig. 5. — Sectiou No. 1.S4 through embryo LXXXVI.
  
  
Fig. (i,— Sectiou No. 302 througb embryo LXXXVI
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Fig. (i,— Sectiou No. 302 through embryo LXXXVI
  
  
Fig. 7. — Section No. KIO tbrounb embryo XLV, x lo duimeters.
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Fig. 7. — Section No. KIO through embryo XLV, x lo duimeters.
  
  
Fig. 8.— Section 142 tbrougb embryo XLV.
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Fig. 8.— Section 142 through embryo XLV.
  
  
  
Fig. 9. — Sectiou 14.5 tbrouffb embryo XLV.
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Fig. 9. — Sectiou 14.5 through embryo XLV.
  
  
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Fig. 10. — Section No. 92 tUrougb embryo XCV.
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Fig. 10. — Section No. 92 through embryo XCV ({{CE95}}).
  
  
  
Fig. 11.— Section No. lUO tlirough embryo XCV.
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Fig. 11.— Section No. lUO through embryo XCV ({{CE95}}).
  
  
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Fig. 13.— .Section No. UIC. tUronsli eniliryo XCV.
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Fig. 13.— .Section No. UIC. through eniliryo XCV ({{CE95}}).
  
  
  
Fig. 13.— Section No. lOS through embryo XCV.
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Fig. 13.— Section No. lOS through embryo XCV ({{CE95}}).
  
  
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the following sections may have a ventrocerebral, a ventral, a veutrospinal and a dorsal edge.
 
  
 
The nucleus pontis ventralis is a solid mass of cells continuous with the raphe. The nucleus pontis dorsalis ia divided into right and left halves not continuous in the middle line. The ventral fibre bundle passes between the ventral and dorsal nuclei except at their extreme lateral parts, where the cerebral ends of the two nuclei are united.
 
The nucleus pontis ventralis is a solid mass of cells continuous with the raphe. The nucleus pontis dorsalis ia divided into right and left halves not continuous in the middle line. The ventral fibre bundle passes between the ventral and dorsal nuclei except at their extreme lateral parts, where the cerebral ends of the two nuclei are united.
  
Section No. 13G is 0.05 mm. to the right of the middle line. On the right side the nucleus pontis ventralis is separated from the raphe by the ventral liljre bundle and nucleus extends across the middle line. On the left side the two ends of the nucleus pontis dorsalis are separated from the rajiho by the ventral fibre bundle and mantle layer. On the veutrospinal surface at the level of the nervus facialis is a deeply stained mass of cells, " H." This mass is continuous opposite the nervus trigeminus with the nucleus pontis; spinalward, dorsalward and lateralward it extends to the ventricular epithelium of the medulla oblongata. In the medulla is a cell-mass, " T," on the medial side of the corpus restiforme. and reaching from the fourth ventricle to the ventrospinal surface. Between " T " and the nucleus pontis dorsalis is a small round mass, " S," a little more deeply stained than the rest of the mantle layer.
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Section No. 13G is 0.05 mm. to the right of the middle line. On the right side the nucleus pontis ventralis is separated from the raphe by the ventral liljre bundle and nucleus extends across the middle line. On the left side the two ends of the nucleus pontis dorsalis are separated from the raphe by the ventral fibre bundle and mantle layer. On the veutrospinal surface at the level of the nervus facialis is a deeply stained mass of cells, " H." This mass is continuous opposite the nervus trigeminus with the nucleus pontis; spinalward, dorsalward and lateralward it extends to the ventricular epithelium of the medulla oblongata. In the medulla is a cell-mass, " T," on the medial side of the corpus restiforme. and reaching from the fourth ventricle to the ventrospinal surface. Between " T " and the nucleus pontis dorsalis is a small round mass, " S," a little more deeply stained than the rest of the mantle layer.
  
 
Section No. 143 is 3.5 mm. to the left of the middle line and shows only the left side of the pons. Between the nuclei pontis is the ventral fibre bundle. The nucleus pontis dorsalis is in the mantle layer; in its spinal end is a small unstained space. On the ventrospinal surface is the uuiss " H." Medial from the corpus restiforme is a round, deeply stained area " S." Near the fourth ventricle are several dark masses just like those in section 136.
 
Section No. 143 is 3.5 mm. to the left of the middle line and shows only the left side of the pons. Between the nuclei pontis is the ventral fibre bundle. The nucleus pontis dorsalis is in the mantle layer; in its spinal end is a small unstained space. On the ventrospinal surface is the uuiss " H." Medial from the corpus restiforme is a round, deeply stained area " S." Near the fourth ventricle are several dark masses just like those in section 136.
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Section No. 145 is 0.4 mm. to the left of the middle line. The nuclei pontis ventralis and dorsalis are continuous at their cerebral ends. Between them is the ventral fibre bundle. Opposite the radi.x N. cochleae is " H," and median from it a cylindrical-shaped area. Between the cerebellum and the pons is an unstained area, the corpus restiforme.
 
Section No. 145 is 0.4 mm. to the left of the middle line. The nuclei pontis ventralis and dorsalis are continuous at their cerebral ends. Between them is the ventral fibre bundle. Opposite the radi.x N. cochleae is " H," and median from it a cylindrical-shaped area. Between the cerebellum and the pons is an unstained area, the corpus restiforme.
  
Embryo No. XCV is 46 mm. long and cut into serial sagittal sections. The nucleus pontis is a solid mass of cells on the ventral surface of the pons, which has increased in size and measures 3 mm. in cerebrospinal, 4.6 mm. in transverse, and 0.5 mm. in ventrodorsal diameter. The ventral fibre bundle divides into two masses, the larger passes dorsal to the nucleus, the smaller through it.
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Embryo No. XCV ({{CE95}}) is 46 mm. long and cut into serial sagittal sections. The nucleus pontis is a solid mass of cells on the ventral surface of the pons, which has increased in size and measures 3 mm. in cerebrospinal, 4.6 mm. in transverse, and 0.5 mm. in ventrodorsal diameter. The ventral fibre bundle divides into two masses, the larger passes dorsal to the nucleus, the smaller through it.
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Section No. 93 is 0.3 mm. to the left of the middle line. The nucleus pontis is a solid nuiss of cells. Dorsal from it is a dark wedge-sluiped area; its ventral surface reaches as far as the nucleus pontis and extends 0.4 mm. beyond the middle line on each side, the dorsal surface is continuous with tlie ependymal epithelium in the middle line and for a distance ol 0.3 mm. to the right. This area contains ventrodorsal markings, and small masses of cells staining more deeply than the rest of the tissue of the wedge between them. On the floor of the fourth ventricle just cerebral from the pontal flexure are two dark round cell-masses, " M," which extend through a few sectjons on either side of the middle line, but in the middle line are overlapped by the greatly thickened ependymal ejiitlielium. On the ventral surface of the medulla oblongata is the ventral fibre bundle. Near the dorsal surface cerebral from the pontal flexure is the dorsal fibre liundle. The mantle layer contains the curved longitudinal striatiou, and in the isthmus is more deeply stained than in the medulla, and also contains blood-spaces. Next the epen(lynuil cpitlielium the mantle layer of the medulla [iresents a unit'onn appearance, and in the isthmus it contains several darker masses ol' cells.
  
Section No. 93 is 0.3 mm. to the left of the middle line. The nucleus pontis is a solid nuiss of cells. Dorsal from it is a dark wedge-sluiped area; its ventral surface reaches as far as the nucleus pontis and extends 0.4 mm. beyond the middle line on each side, the dorsal surface is continuous with tlie ependymal epithelium in the middle line and for a distance ol 0.3 mm. to the right. This area contains ventrodorsal markings, and small masses of cells staining more deeply than the rest of the tissue of the wedge between them. On the floor of the fourth ventricle just cerebral from the pontal flexure are two dark round cell-masses, " M," which extend through a few sectjons on either side of the middle line, but in the middle line are overlapped by the greatly thickened ependymal ejiitlielium. On the ventral surface of the medulla oblongata is the ventral fibre bundle. Near the dorsal surface cerebral from the pontal flexure is the dorsal fibre liundle. The mantle layer contains the curved longitudinal striatiou, and in the isthmus is more deei)ly stained than in the medulla, and also contains blood-spaces. Next the epen(lynuil cpitlielium the mantle layer of the medulla [iresents a unit'onn appearance, and in the isthnuis it contains several darker masses ol' cells.
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Section No. lOO is 0.6 mm. to the right of the middle line. The s]>iiwl portion of the nucleus pontis is divided into ventral and dorsal parts by a clear area, containing a few dark strands composed of cells. " M is still present; between it and the nucleus pontis are several small cell-masses. The ventral fibre bundle is on the surface of the medulla and next the dorsal side of the nucleus pontis. The mantle layer contains the curved longitudinal striatiou and blood-spaces. Between the dorsal fibie bundle and the ependymal epithelium arc numerous dark cell-masses.
  
Section No. lOO is 0.6 mm. to the right of the middle line. The s]>iiwl portion of the nucleus pontis is divided into ventral and dor.^al parts by a clear area, containing a few dark strands com}iosed of cells. " M is still present; between it and the nucleus pontis are several small cell-masses. The ventral fibre bundle is on the surface of the medulla and next the dorsal side of the nucleus pontis. The mantle layer contains the curved longitudinal striatiou and blood-spaces. Between the dorsal fibie bundle and the ependymal epithelium arc numerous dark cell-masses.
 
  
 
Section No. 106 is 1 mm. right of the middle line. The nucleus pontis is more unevenly stained. Its cerebral end is divided into ventral and dorsal parts by an unstained area, which is continuous with the ventral fibre bundle. The fibre bundle extends the entire length of this section. It is now seen that this fibre bundle has an oblique direction through the cerebrolateral and spinomedial portion of the rhombencephalon. The appearance of the mantle layer is the same as in the preceding section; between the nucleus pontis and the nucleus olivaris a foAV of tlie curved striations are more deeply stained than the rest, S."
 
Section No. 106 is 1 mm. right of the middle line. The nucleus pontis is more unevenly stained. Its cerebral end is divided into ventral and dorsal parts by an unstained area, which is continuous with the ventral fibre bundle. The fibre bundle extends the entire length of this section. It is now seen that this fibre bundle has an oblique direction through the cerebrolateral and spinomedial portion of the rhombencephalon. The appearance of the mantle layer is the same as in the preceding section; between the nucleus pontis and the nucleus olivaris a foAV of tlie curved striations are more deeply stained than the rest, S."
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Section No. 108 is 1.4 mm. to the left of the middle line. The nucleus pontis is a smaller mass, unevenly stained owing to the presence of large numbers of white spots (nerve-fibres). Dorsal from it is the ventral fibre himdle. The mantle layer appeal's as before but the mass " M " is not present. Between the nucleus pontis and the nucleus olivaris are a few small cell-masses, and several more are scattered throughout the mantle layer of the isthmus.
 
Section No. 108 is 1.4 mm. to the left of the middle line. The nucleus pontis is a smaller mass, unevenly stained owing to the presence of large numbers of white spots (nerve-fibres). Dorsal from it is the ventral fibre himdle. The mantle layer appeal's as before but the mass " M " is not present. Between the nucleus pontis and the nucleus olivaris are a few small cell-masses, and several more are scattered throughout the mantle layer of the isthmus.
  
Embryo No. XCYI is 48 mm. long and cut into serial sagittal sections. The nucleus pontis has increased in the ventrodorsal diameter. The appearance of this specimen is almost identical with that of No. XCV, and is only of interest because it corroborates what was found there. So I have not thought it necessary to add illustrations. Just spinal from the nervus trigeminus the nucleus pontis is continuous with a mass of cells which reaches to the ependymal epithelium of the fourth ventricle. The ventral fibre bundle passes partly along the dorsal surface of the nucleus pontis and partly through it. Among the latter fibres are a few scattered strands of cells resembling more the appearance of the pons at later stage. The wedged-shaped area and the cell-mass appear as before.
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Embryo No. XCVI ({{CE95}}) is 48 mm. long and cut into serial sagittal sections. The nucleus pontis has increased in the ventrodorsal diameter. The appearance of this specimen is almost identical with that of No. XCV, and is only of interest because it corroborates what was found there. So I have not thought it necessary to add illustrations. Just spinal from the nervus trigeminus the nucleus pontis is continuous with a mass of cells which reaches to the ependymal epithelium of the fourth ventricle. The ventral fibre bundle passes partly along the dorsal surface of the nucleus pontis and partly through it. Among the latter fibres are a few scattered strands of cells resembling more the appearance of the pons at later stage. The wedged-shaped area and the cell-mass appear as before.
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The histological structure of these specimens is as follows: The ependymal epithelium contains large, dark, densely packed, round and oval cells. The mantle layer in the earlier stages consists of round cells and a few oval cells. In embryo No. LXXV an unstained fibrous network is seen and the round cells are scattered through it, which in No. LXXXVI and No. XLV are more closely packed together. In the older specimens neuroblasts of the mantle layer point in various directions, a good many of them direct their axones ventralward, and many roimd cells are still seen. Most of the neurolilasts are now arranged in definite groups; between them is an unstained fibrous network which contains spongioblasts. Both the nucleus pontis and the mass " M " are composed of round cells in all the sections. The mass " H " consists of round cells, resembling in size and staining reaction those of the ependynial epithelium. The raphe appears in two specimens; it consists of filjres which interlace across the middle line, round cells, ami in the frontal sections a few oval cells with their long axis transversely directed. In sagittal sections the raphe is not seen; its fibres, if present, would be cut in cross-sections.
 
The histological structure of these specimens is as follows: The ependymal epithelium contains large, dark, densely packed, round and oval cells. The mantle layer in the earlier stages consists of round cells and a few oval cells. In embryo No. LXXV an unstained fibrous network is seen and the round cells are scattered through it, which in No. LXXXVI and No. XLV are more closely packed together. In the older specimens neuroblasts of the mantle layer point in various directions, a good many of them direct their axones ventralward, and many roimd cells are still seen. Most of the neurolilasts are now arranged in definite groups; between them is an unstained fibrous network which contains spongioblasts. Both the nucleus pontis and the mass " M " are composed of round cells in all the sections. The mass " H " consists of round cells, resembling in size and staining reaction those of the ependynial epithelium. The raphe appears in two specimens; it consists of filjres which interlace across the middle line, round cells, ami in the frontal sections a few oval cells with their long axis transversely directed. In sagittal sections the raphe is not seen; its fibres, if present, would be cut in cross-sections.
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==Summary==
 
==Summary==
  
The main nucleus pontis is situated on the ventral surface of the rhombencephalon at the level of the pontal flexure. In the specimens the nuclei pontis are first seen on the surface
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The main nucleus pontis is situated on the ventral surface of the rhombencephalon at the level of the pontal flexure. In the specimens the nuclei pontis are first seen on the surface and in the ventral part of the mantle layer of the lateral part of the pons Varolii. Ventral to all, in this early stage, except the mass of cells " H," is the ventral fibre bundle. In the second embryo the nucleus pontis ventralis extends across the middle line of the rhombencephalon and the nuclei pontis dorsales are separated from its lateral part by the ventral fibre bundle. The nuclei pontis dorsales next form two solid masses, reaching almost to the middle line. They are still separated by the ventral fibre bundle from the nucleus pontis ventralis, except at the extreme lateral ends, where they are continuous with each other. Next the nucleus pontis becomes a solid shell on the ventral surface cut by a .small branch from the ventral fibre bundle. After the sixth month the pons consists mainly of fibres and scattered groiips of cells which increase at the expense of the dorsal part of the nucleus, while a narrow ventral nucleus or eell-nuiss is left on the surface.
 
 
 
 
  
and in the ventral part of the mantle layer of the lateral part of the pons Varolii. Ventral to all, in this early stage, except the mass of cells " H," is the ventral fibre bundle. In the second embryo the nucleus pontis ventralis extends across the middle line of the rhombencephalon and the nuclei pontis dorsales are separated from its lateral part by the ventral fibre bundle. The nuclei pontis dorsales next form two solid masses, reaching almost to the middle line. They are still separated by the ventral fibre bundle from the niicleus pontis ventralis, except at the extreme lateral ends, where they are continuous with each other. Next the nucleus pontis becomes a solid shell on the ventral surface cut by a .small branch from the ventral fibre bundle. After the sixth month the pons consists mainly of fibres and scattered groiips of cells which increase at the expense of the dorsal part of the nucleus, while a narrow ventral nucleus or eell-nuiss is left on the surface.
 
  
 
The neuroblasts of the pons are continuous with the epithelium of the floor of the fourth ventricle:
 
The neuroblasts of the pons are continuous with the epithelium of the floor of the fourth ventricle:
  
(1) By the cell-mass " H " at the lateral end of the nucleus pontis.
+
# By the cell-mass " H " at the lateral end of the nucleus pontis.
 
+
# By the round cells in the rajjhe.
(2) By the round cells in the rajjhe.
+
# In the middle line by the neuroblast in tlie wedge, which connects both the ependymal epithelium and the cellmass " M " w ith the nucleus pontis.
 
 
(3) In the middle line by the neuroblast in tlie wedge, which connects both the ependymal epithelium and the cellmass " M " w ith tlie nucleus pontis.
 
  
  

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Long M. On the development of the nuclei pontis during the second and third months of embryonic life. (1901) Johns Hopkins Hospital Bulletin 12: 123-126.

Carnegie Collection: 45, 75, 86, 95

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On the Development of the Nuclei Pontis during the Second and Third months of Embryonic Life

By Margaret Long.

[From the Anatomical Laboratory of Johna Hopkins Vnu'erxitij.)

This work was undertaken in the fall of 1899 at the suggestion of Doctor Barker, and has been carried out with his assistance. The specimens used are human embryos and were very kindly lent by Doctor Mall from his collection.

  • The numbers of the embryos correspond with their numbers in the embryological cabinet of the Anatomical Laboratory of the Johns Hopkins University.


The following embryos are described in the order of their probable age, as estimated by their length and by the develojiment in the rhombencepbalon. The arrangement of the cerebral nerves and the general appearance of the medulla oblongata agree with the His models and with the description given by His in "Die Entwicklung des menscblicben Kautenhirns"; a description of these is accordingly unnecessary. Each embryo has been studied in serial sections and from tliese sections a few, at different stages of development,. have been selected as characteristic of the structure of the pons, its nuclei and fibres. To make the work complete it will be necessary to study more embryos at intermediate stages between the five given here, and others from the third montli up to the adult pons.


Embryo No. LXXV {{{CE75}}} is 30 mm. long and has been cut into serial sagittal sections. The nuclei, whiuli I have designated as " B," " C," " D," " E " and " H " in the various sections, are masses of cells distributed through the ventral part of the mantle layer (Mantelsehicht of His) at or near the level of the pontal flexure. The most medial of these nuclei extend to within 0.7 mm. of the middle line. An unstained fibre bundle can he .seen on the surface of the rhombencephalon ventral to the mantle layer throughout its entire length.


Section No. 73 is 2.1 mm. to the left of the middle line (Fig. 1). Near the ventral surface on the cerebral side o.f the nervus trigeminus is a well defined cell-mass, '" B.' On the ventral surface opposite the nervus acusticus is a deeply stained cell-mass, " IT," which (wlien followed in the series) is seen to extend lateralward and spinalward to the floor of the fourth ventricle at the Junction of the latter with the telachorioidea. The section of the mantle layer presents longitudinal striations which have a slight ventral convexity. A few of these strands are more deeply stained than th.e rest between the level of the N. trigeminus and that of the N. acusticus. The dark ependymal epithelium and the unstained ventral fibre bundle are evident.

Section No. 91 is 1.2 mm. to the left of the middle line. On the ventral surface of the pons is a delicate shell or mass of cells, " H," continuous lateralward with " H " of the previous section. Between it and the mantle layer is the ventral fibre bundle. Dorsal from " A " is a cell-mass, " C," partially subdivided by a few colorless dorsoventral stripes; ventralward and cerebralward from " C " is another mass, " D," and still more cerebralward and dorsalward are two small deeply stained cellular masses, " E." The mantle layer of the medulla oblongata is deeply stained. It contains a diamond-shaped mass, " S," spinalward from " C," the longitudinal striations mentioned in the previous section, and an unstained dorsal filire bundle (DF).

Section No. 96 is 1.05 mm. to the left of the middle line. "H" and "C" are still present. The ventral fibre bimdle passes partly along the dorsal surface of "H" and partly between " C " and " E." Just cerebralward from the pontal flexure, close to the floor of the ventricle, is " M, an oval mass of cells witli a clear unstained area behind at its spinal end, and measuring 0.8 mm. in transverse diameter. The appearance of the mantle layer is the same as before. In its dorsal and cerebral part is seen an unstained dorsal fibre bundle.


Embryo No. LXXXVI (86) is 30 mm. long and has been cut into serial coronal sections. There is ventralward a definite mass which I have designated as the nucleus pontis ventralis; it is about 1 mm. long by 3 mm. wide. The raphe enters this nucleus in the middle line. Dorsal from its lateral part are several scattered masses which 1 have designated, tentatively, the nuclei pontis dorsales. The unstained ventral fibre bundle is dorsal from the nucleus pontis ventralis.


Section No. 175 is spinalward from the masses mentioned. On the ventral surface medialward from the nervus acusticus (-A^.l ) is the cell-mass " H." Followed through the series this cell-mass extends spinalward, dorsalward and lateralward to the ependymal epithelium of the fourth ventricle; cerebralward, it is medial to the nervus trigeminus and continuous with the nucleus pontis. Taken in order from the raphe lateralward in the mantle layer are the nucleus olivaris superior (8) and the superior olivary complex {S}, the ascending and descending parts of the root of the nervus facialis, the nucleus nervi facialis {NNP), and the corpus restiforme {OR). On the floor of the fourth ventricle are the nucleus nervi abducentis (NNA) and the nucleus N. vestibuli (radicis deseendentis), {III? I'D); further lateralward are the nuclei N. cochleae, namely the nucleus N. eochleffi dorsnlis (NRCD) and the nucleus N. cochlea; ventralis (NNCV). The unstained area is the ventral fibre bundle (I'-P') Section No. 184 is 0.45 mm. cerebralward from the preceding section. In the mantle layer are seen in order the nucleus olivaris superior, (S), the nucleus nervi facialis (NNF). and parts of the ascending and descending limbs of the nervus facialis. "H" is on the ventral surface lateral from tlie nervus facialis. On the floor of the fourth ventricle is the nucleus N. vestibuli medialis et radicis descendentis (NNV).

Section No. 202 is 0.9 mm. cereliralward from section 184. The nucleus pontis ventralis reaches lateralward as far as the nervus trigeminus. In the middle line the raphe extends from the nucleus pontis to the ependymal epithelium. The nuclei pontis dorsales consist of several irregular masses, " A," " B," " C," and " E," and a more ventral and lateral mass. " D." These nuclei extend through the pons for a distance of 0.5 mm. in the cerebrospinal diameter. Between these ventral and dorsal nuclei is the unstained ventral fibre bundle. Lateral from the nervus trigeminus are the nucleus nervus trigeminus ascendcns and an unstained area.

Embryo No. XLV (45) is 28 mm. long, and has been cut in serial sections, which divide the pons in an oblique direction in the following way: Instead of corresponding to the transverse diameter of the pons the left side of each section is further spinalward than the right side of the same section. The ventrodor.sal plane of the section is also oblique, so that in each section the left half of the dorsal surface is the more lateral, but in the right half of the pons the dorsal surface is more medial than the ventral. In other words, the first section removes a small portion of the pons about the cerebral ventral corner on the left side, and at the dorsal-spinnl angle on the right side.

The nucleus pontis, as seen in this series, is on the surface of the rhombencephalon and follows the curve of the pontal flexure so that it is crescentic in shape, with a ventral convex surface and cerebral and spinal ends or horns. Consequently the following sections may have a ventrocerebral, a ventral, a veutrospinal and a dorsal edge.


PLATE XXI.

Fig. 1. — Section through the pons of embryo LXXV, oO mm. lous; X 1.5 diameters.


Fig. 3. — Section No. 91 of embryo LXXV, x 1.5 diameters.


Fig. 3.— Section No. 90 of embryo LXXV.


Fig. 4. — Section No. 17.5 through the brain of embryo LXXXVI, oO mm. long, x 15 diameters.


PLATE XXII.


Fig. 5. — Sectiou No. 1.S4 through embryo LXXXVI.


Fig. (i,— Sectiou No. 302 through embryo LXXXVI


Fig. 7. — Section No. KIO through embryo XLV, x lo duimeters.


Fig. 8.— Section 142 through embryo XLV.


Fig. 9. — Sectiou 14.5 through embryo XLV.


PLATE XXIII.


Fig. 10. — Section No. 92 through embryo XCV (95).


Fig. 11.— Section No. lUO through embryo XCV (95).


PLATE XXIV.


Fig. 13.— .Section No. UIC. through eniliryo XCV (95).


Fig. 13.— Section No. lOS through embryo XCV (95).




The nucleus pontis ventralis is a solid mass of cells continuous with the raphe. The nucleus pontis dorsalis ia divided into right and left halves not continuous in the middle line. The ventral fibre bundle passes between the ventral and dorsal nuclei except at their extreme lateral parts, where the cerebral ends of the two nuclei are united.

Section No. 13G is 0.05 mm. to the right of the middle line. On the right side the nucleus pontis ventralis is separated from the raphe by the ventral liljre bundle and nucleus extends across the middle line. On the left side the two ends of the nucleus pontis dorsalis are separated from the raphe by the ventral fibre bundle and mantle layer. On the veutrospinal surface at the level of the nervus facialis is a deeply stained mass of cells, " H." This mass is continuous opposite the nervus trigeminus with the nucleus pontis; spinalward, dorsalward and lateralward it extends to the ventricular epithelium of the medulla oblongata. In the medulla is a cell-mass, " T," on the medial side of the corpus restiforme. and reaching from the fourth ventricle to the ventrospinal surface. Between " T " and the nucleus pontis dorsalis is a small round mass, " S," a little more deeply stained than the rest of the mantle layer.

Section No. 143 is 3.5 mm. to the left of the middle line and shows only the left side of the pons. Between the nuclei pontis is the ventral fibre bundle. The nucleus pontis dorsalis is in the mantle layer; in its spinal end is a small unstained space. On the ventrospinal surface is the uuiss " H." Medial from the corpus restiforme is a round, deeply stained area " S." Near the fourth ventricle are several dark masses just like those in section 136.

Section No. 145 is 0.4 mm. to the left of the middle line. The nuclei pontis ventralis and dorsalis are continuous at their cerebral ends. Between them is the ventral fibre bundle. Opposite the radi.x N. cochleae is " H," and median from it a cylindrical-shaped area. Between the cerebellum and the pons is an unstained area, the corpus restiforme.

Embryo No. XCV (95) is 46 mm. long and cut into serial sagittal sections. The nucleus pontis is a solid mass of cells on the ventral surface of the pons, which has increased in size and measures 3 mm. in cerebrospinal, 4.6 mm. in transverse, and 0.5 mm. in ventrodorsal diameter. The ventral fibre bundle divides into two masses, the larger passes dorsal to the nucleus, the smaller through it.

Section No. 93 is 0.3 mm. to the left of the middle line. The nucleus pontis is a solid nuiss of cells. Dorsal from it is a dark wedge-sluiped area; its ventral surface reaches as far as the nucleus pontis and extends 0.4 mm. beyond the middle line on each side, the dorsal surface is continuous with tlie ependymal epithelium in the middle line and for a distance ol 0.3 mm. to the right. This area contains ventrodorsal markings, and small masses of cells staining more deeply than the rest of the tissue of the wedge between them. On the floor of the fourth ventricle just cerebral from the pontal flexure are two dark round cell-masses, " M," which extend through a few sectjons on either side of the middle line, but in the middle line are overlapped by the greatly thickened ependymal ejiitlielium. On the ventral surface of the medulla oblongata is the ventral fibre bundle. Near the dorsal surface cerebral from the pontal flexure is the dorsal fibre liundle. The mantle layer contains the curved longitudinal striatiou, and in the isthmus is more deeply stained than in the medulla, and also contains blood-spaces. Next the epen(lynuil cpitlielium the mantle layer of the medulla [iresents a unit'onn appearance, and in the isthmus it contains several darker masses ol' cells.

Section No. lOO is 0.6 mm. to the right of the middle line. The s]>iiwl portion of the nucleus pontis is divided into ventral and dorsal parts by a clear area, containing a few dark strands composed of cells. " M is still present; between it and the nucleus pontis are several small cell-masses. The ventral fibre bundle is on the surface of the medulla and next the dorsal side of the nucleus pontis. The mantle layer contains the curved longitudinal striatiou and blood-spaces. Between the dorsal fibie bundle and the ependymal epithelium arc numerous dark cell-masses.


Section No. 106 is 1 mm. right of the middle line. The nucleus pontis is more unevenly stained. Its cerebral end is divided into ventral and dorsal parts by an unstained area, which is continuous with the ventral fibre bundle. The fibre bundle extends the entire length of this section. It is now seen that this fibre bundle has an oblique direction through the cerebrolateral and spinomedial portion of the rhombencephalon. The appearance of the mantle layer is the same as in the preceding section; between the nucleus pontis and the nucleus olivaris a foAV of tlie curved striations are more deeply stained than the rest, S."

Section No. 108 is 1.4 mm. to the left of the middle line. The nucleus pontis is a smaller mass, unevenly stained owing to the presence of large numbers of white spots (nerve-fibres). Dorsal from it is the ventral fibre himdle. The mantle layer appeal's as before but the mass " M " is not present. Between the nucleus pontis and the nucleus olivaris are a few small cell-masses, and several more are scattered throughout the mantle layer of the isthmus.


Embryo No. XCVI (95) is 48 mm. long and cut into serial sagittal sections. The nucleus pontis has increased in the ventrodorsal diameter. The appearance of this specimen is almost identical with that of No. XCV, and is only of interest because it corroborates what was found there. So I have not thought it necessary to add illustrations. Just spinal from the nervus trigeminus the nucleus pontis is continuous with a mass of cells which reaches to the ependymal epithelium of the fourth ventricle. The ventral fibre bundle passes partly along the dorsal surface of the nucleus pontis and partly through it. Among the latter fibres are a few scattered strands of cells resembling more the appearance of the pons at later stage. The wedged-shaped area and the cell-mass appear as before.


The histological structure of these specimens is as follows: The ependymal epithelium contains large, dark, densely packed, round and oval cells. The mantle layer in the earlier stages consists of round cells and a few oval cells. In embryo No. LXXV an unstained fibrous network is seen and the round cells are scattered through it, which in No. LXXXVI and No. XLV are more closely packed together. In the older specimens neuroblasts of the mantle layer point in various directions, a good many of them direct their axones ventralward, and many roimd cells are still seen. Most of the neurolilasts are now arranged in definite groups; between them is an unstained fibrous network which contains spongioblasts. Both the nucleus pontis and the mass " M " are composed of round cells in all the sections. The mass " H " consists of round cells, resembling in size and staining reaction those of the ependynial epithelium. The raphe appears in two specimens; it consists of filjres which interlace across the middle line, round cells, ami in the frontal sections a few oval cells with their long axis transversely directed. In sagittal sections the raphe is not seen; its fibres, if present, would be cut in cross-sections.

Summary

The main nucleus pontis is situated on the ventral surface of the rhombencephalon at the level of the pontal flexure. In the specimens the nuclei pontis are first seen on the surface and in the ventral part of the mantle layer of the lateral part of the pons Varolii. Ventral to all, in this early stage, except the mass of cells " H," is the ventral fibre bundle. In the second embryo the nucleus pontis ventralis extends across the middle line of the rhombencephalon and the nuclei pontis dorsales are separated from its lateral part by the ventral fibre bundle. The nuclei pontis dorsales next form two solid masses, reaching almost to the middle line. They are still separated by the ventral fibre bundle from the nucleus pontis ventralis, except at the extreme lateral ends, where they are continuous with each other. Next the nucleus pontis becomes a solid shell on the ventral surface cut by a .small branch from the ventral fibre bundle. After the sixth month the pons consists mainly of fibres and scattered groiips of cells which increase at the expense of the dorsal part of the nucleus, while a narrow ventral nucleus or eell-nuiss is left on the surface.


The neuroblasts of the pons are continuous with the epithelium of the floor of the fourth ventricle:

  1. By the cell-mass " H " at the lateral end of the nucleus pontis.
  2. By the round cells in the rajjhe.
  3. In the middle line by the neuroblast in tlie wedge, which connects both the ependymal epithelium and the cellmass " M " w ith the nucleus pontis.



Cite this page: Hill, M.A. (2020, March 31) Embryology Paper - On the development of the nuclei pontis during the second and third months of embryonic life (1901). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_On_the_development_of_the_nuclei_pontis_during_the_second_and_third_months_of_embryonic_life_(1901)

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