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Updated: May 4, 2025
When the brain is cut, it is found to be composed of two substances, essentially different in construction and function the cortical and the medullary. The first is small in quantity, and principally concerned in the food and reproduction of the animal, and the cineritious in a great measure the register of the mind.
In fact, bass will not be induced to decently decease by any civilized process short of a powerful shock from a voltaic pile administered in the region of their medulla oblongata. Of course, one cannot be expected to carry about a voltaic pile and go hunting for the medullary recesses of a savage and turbulent fish.
These nerve-centers, viewed as magnets of electro-vitality, require to be regarded as having each a positive nucleus in the interior, on which are ranged the negative ends of the currents which go out from this positive nucleus in every direction to the surface of the medullary organ so radiating, as it were, from center to periphery.
Even in the Platodes, especially the Turbellaria, we find an independent nervous system, which has separated from the outer skin. From this rudimentary structure has been developed the elaborate central nervous system of the higher animals. But the medullary tube of the Vertebrates originates in the same way.
Rows of these tubercles are arranged spirally round each root, which have always a medullary axis and woody system much resembling that of Sigillaria, the structure of the vessels being, like it, scalariform. Fragment of coniferous wood, Dadoxylon, of Endlicher, fractured longitudinally; from Coalbrook Dale. W.C. Williamson. Bark. b. Medulla or pith. d.
It consists of two layers, an outer fibrous and an inner cellular layer; the cells, which are called osteoblasts, are continuous with those lining the Haversian canals and the medullary cavity. The arrangement of the blood vessels determines to some extent the incidence of disease in bone.
But it would be equally absurd to presuppose that these several functions can be disarranged for months, without more or less disorganisation of the medullary, or even of the cineritious, matter of the encephialon.
The presence of fat and bony particles in the pus confirms the medullary origin of the suppuration. If an incision is made, the periosteum is found to be raised from the bone; the extent of the bare bone will be found to correspond fairly accurately with the extent of the lesion in the marrow. Local Complications.
These medullary swellings join together over the furrow, and form a tube; in this case, again, the neural or medullary tube is at first open in front, and connected with the primitive gut behind by the neurenteric canal. Further, in the Ascidia-larva also the two permanent apertures of the alimentary canal only appear later, as independent and new formations.
This groove is, of course, the dorsal furrow, and the swellings are the dorsal or medullary swellings; they form the first structure of the central nervous system, the medullary tube. The medullary swellings now rise higher; the groove between them becomes deeper and deeper.
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