A concept of the development of the mammalian rhombencephalon based on physical rotational forces.
The premammalian forms do not show the metencephalic and myelencephalic divisions of the rhombencephalon. The seven longitudinal grey columns, in relation to the seven nerve components are direct cranial uninterrupted continuations from the spinal cord. The isthmus rhombencephali is a tubular structure. The phylogenetically ancient ependyma rich in tanycytes lines the fourth ventricle. The neural canal does not open into the subarachnoid space and the ependyma never becomes directly continuous with the pia mater. On the other hand, in mammals, the rhombencephalon is divided into the metencephalon and myelencephalon. The seven longitudinal grey columns get fragmented and their cell masses undergo migrations. The isthmus loses its tubular nature and undergoes modifications. The fourth ventricle opens into the subarachnoid space through three openings. The phylogenetically ancient ependyma is retained as a continuous structure only along the inferolateral angle of the fourth ventricle. At the openings of the lateral recesses, the ependyma becomes directly continuous with the pia, a neural crest derivative. The oval bundle, the corpus trapezoideum and the myelencephalic component of the nuclei pontis show extensive migrations. The above phenomena can be explained by physical rotation forces and not merely by migrations.
Inamdar
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D000818:Animals; D008322:Mammals / Q000033:anatomy & histology*; D008959:Models, Neurological; D010802:Phylogeny; D011149:Pons / Q000033:anatomy & histology; D012249:Rhombencephalon / Q000033:anatomy & histology*; D012399:Rotation; D013314:Stress, Mechanical