Talk:Paper - On the embryology of the corpus ponto-bulbare and its relation to the development of the pons (1909)

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On The Embryology Of The Corpus Ponto-Bulbare And Its Relation To The Development Of The Pons

Essick CR. On the embryology of the corpus ponto-bulbare and its relation to the development of the pons (1909) Anat. Rec. 3: 254-256.

By Chables R. EssicK. From the Anatomical Laboratory, John^ Hopkins University.

The study of the embryology of the Corpus Ponto-bulbare throws considerable light on the adult body which I described for the human hind-brain.^ In the adult was found a mass of cells and fibres normally present in all brains but showing considerable variations in its size and development. It was described as arising more or less indefinitely from the transverse fibres of the pons mesial to the fifth nerve and gathering into a well-defined bundle which curved into the long axis of the brain behind this nerve and then passed between the seventh and eighth cranial nerves. It continued backward with a dorsal curve, encircling the dorsal cochlear nucleus, and usually ending as a free tip projecting into the roof of the fourth ventricle. The study of its origin shows it to begin at the caudal end and extend cephalad, hence the embryonic description must be reversed. Whereas the mature body varies so greatly in development, often differing on the two sides of the same brain, the embryonic counterpart is remarkably constant. In addition it must be kept in mind that the ponto-bulbar body is present before any pontine formation occurs, appearing first as a thickening in the secondary "Rautenlippe" of His, just behind the dorsal cochlear nucleus. Later the cells migrate over the restiform body and advance to the pontine flexure between the facial and acoustic nerves.

The fact that in the adult this structure varies in amount of development; the fact that in the embryo it is so constant; and finally the fact that at first it is so large when compared to the pons, at once suggests that we are dealing with something which possesses more function in the embryo than in the adult. This study demonstrates that its function is to furnish a path by which tells, arisiiic: at the lateral margins of the medulla, wander to the ventral surface of the brain and form the main mass of pontine nuclei.

In the 20 mm. embryo of the Mall Collection (Xo. 22) immediately caudad to the dorsal cochlear nucleus, appears a circumscrihed thickening of the secondary "Kautenlippe" in which an active division/ of cells can be made out. This is the point of origin for the pontine cells which travel down the path described for the corpus pontobulbare.

C. R. Essick, The Corpus Poiito-biiU)are, a hitherto undescribed Nucleus In the Human Hind-Brain. Amer. Jour. Anat., vol. vU, p. 119.

In the 23 mm. embryo (No. 382), the ventricular margin just behind the dorsal cochlear nucleus is rich in mitotic figures, and here due to the active proliferation of cells, the "Kautenlippe" is markedly thickened. From this point as a starting place deeplystaining elongated nuclei extend laterally aroimd the restiform body and pass forward between the facial and acoustic nerves as far as the trigeminal nerve. The sheet of nuclei has become much thinned out in its cerebral portion, so that the layer is only one to two cells thick at the fifth nerve, and the same condition obtains for its mesial border, which is rapidly lost after the sagittal plane of the emergent facial is passed. The distribution of mitotic figures is striking. Numerous karyokinetic figures appear in every section around the central canal, but as soon as this is left, only an occasional dividing cell is made out and the diflBculty in finding them increases the farther cephalad one passes in sections. Clearly then we are dealing not with a growth by extension but an actual migration of cells. This embryo has no pons.

In the 28 mm. embryo (No. 75), the active formation of cells still continues in the domain of the "Rautenlippe" caudal to the dorsal cochlear nucleus and the entire body is much thickened. Cephalad it can now be traced almost to the mid-line on both sides, arching over to the pontine flexure from the lateral portions and presenting an advancing edge of only one or two cells in thickness.

In the 30 mm. embryo (No. 45), the cells of both sides have met and fused across the mid-line directly over the pontine flexure and the primitive anlage of the pons is formed. In the older embryos the addition of cells continues so that there is a heaping up of cells over the mid-line forming the well known crescentic shape which the pons gives in cross-section.

The course of the cells, in sections, is not difficult to follow because of their peculiar affinity for stains, a characteristic of all young nuclei, and this property gives a brilliant differentiation of the ponto-bulbar body from the structures with which it oomes into close contact. With the exception of the deeply colored lining which surrounds the ventricular cavity, the porito-bulbar body is the most striking part of sections through this portion of the embryonic medulla and many authors have given good illustrations of the corpus ponto-bulbare, noting its connection with the "Rautenlippe" as well as its extension to the ventral surface of the brain. There has been a failure to connect it with the development of the pons.

This study was greatly aided by sections and dissections of other mammalian embryos where absolutely fresh material is available. This comparative work has simply confirmed the above findings.

A migration of cells from the dorso-lateral margin of the medulla to the ventral portion of the brain has been described by His* for the complex which he designates "die zerrissenen Kerne." To these belong the olives and their neighboring structures. "All of their cells abandon the place where they were originally formed and press through to the mesial lying regions of the medulla. * * * As far as the cells are concerned these structures are, therefore, descendants of the alar plate and morphologically arise from the same longitudinal zone of the medullary tube from which come the higher-lying parts of the brain, i. e., the cerebellum, quadrigeminal bodies, geniculate bodies and the cerebral hemispheres." In the concluding sentence of his classical treatise on the development of the Rhomboid Brain, he mentions his intention to take up the development of the pons and cerebellum and believes that the real key to the development of the former, the pons, will be furnished by the principle of lamina formation. It seems very plausible that this very principle has been observed in the sheet of nuclei arising in the "Rautenlippe" behind the dorsal cochlear nucleus and after encircling the brain for almost 180°, the cells come to rest on the ventral surface of the Rhomboid Brain and later send their processes laterally to form the middle peduncle of the cerebellum. The corpus ponto-bulbare in the fully developed brain represents those cells with their processes which have not descendend to the pons, but lie scattered along the channel where in embryonic life an active migration of cells took place from the ^^Kautenlippe" of the fourth ventricle to the pontine flexure.

W. His, Die Entwick. des Mensch. Raut., 1891.