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Updated: June 4, 2025
"It is not on account of having written several works on the pathological anatomy of medullary lesions, and especially on the alterations of the spinal ganglia, that one acquires authority in a question so comprehensive and so delicate." "Do not be too modest, dear friend. I have had, lately, to consult my Dictionary of Medicine, and at each page your work was quoted.
It will also be seen that the shaft is a hollow cylinder, formed of compact tissue, enclosing a cavity called the medullary canal, which is filled with a pulpy, yellow fat called marrow. The marrow is richly supplied with blood-vessels, which enter the cavity through small openings in the compact tissue. In fact, all over the surface of bone are minute canals leading into the substance.
The chief part of all the sense-organs originates from the skin-sense layer, partly directly from the horny plate, partly from the brain, the foremost part, of the medullary tube, after it has separated from the horny plate.
At the same time, the neural or medullary tube is formed above the chorda, on the dorsal surface, by the closing of the parallel medullary swellings.
Each corpuscle receives the termination of one or more nerve fibers. These, on entering, lose the medullary sheath and separate into a number of branches that penetrate the corpuscle in different directions. The largest of the simple forms of sense organs are bodies visible to the naked eye and called, from their discoverer Pacini, the Pacinian corpuscles.
We meet the same simple medullary tube in the first structure of the ascidia larva, in the same characteristic position, above the chorda. On closer examination we find here also a small vesicular swelling at the fore end of the tube, the first trace of a differentiation of it into brain and spinal cord.
The bones show a feeble shadow with the X-rays, and appear thin and atrophied; the medullary canal is increased at the expense of the cortex. In young infants in whom multiple fractures occur the prognosis as to life is unfavourable, and no satisfactory treatment of the disease has been formulated. If the patient survives, the tendency to fracture gradually disappears.
When we examine the embryology of the human nervous system, we must start from the important fact, which we have already seen, that the first structure of it in man and all the higher Vertebrates is the simple medullary tube, and that this separates from the outer germinal layer in the middle line of the sole-shaped embryonic shield.
These lie parallel in the medullary or central structure, but On reaching the cortical or outer layer, they wind about and interlace, ending, at last, in dilated closed sacs called Malpighian capsules. Vertical Section of the Kidney. Function of the Kidneys. The Malpighian capsules are really the beginning of the tubules, for here the work of excretion begins.
While the medullary groove is sinking in the middle line of the flat dorsal side of the oval embryo, and its parallel edges unite to form the ectodermic neural tube, the single chorda is formed directly underneath them, and on each side of this a parallel longitudinal fold, from the dorsal wall of the primitive gut.
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