Paper - Factors Involved In The Formation Of The Filum Terminale

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Streeter G.L. Factors Involved In The Formation Of The Filum Terminale 1919 Am J Anat. 22:1-11.

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Factors Involved In The Formation Of The Filum Terminale

George L. Streeter

From The Department Of Embryology, Carnegie Institution of Washington, Baltimore, Maryland.

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In a study recently published by the writer1 on the development of the cartilaginous capsule of the ear in human embryos it was pointed out that the changes in size and form which the capsule undergoes during its development are accomplished not only by a progressive differentiation, but also in part by a retrogressive differentiation of its constituent tissues. The margins of the cartilaginous cavities are in a continual state of change; they exhibit an unstable equilibrium between two opposing tendencies: on one hand, toward the deposit of new cartilage, and on the other, toward the excavation of the old. The margins thereby are always advancing; or receding, and as a result of this there is provided a suitable suite of chambers for the contained membranous labyrinth in all stages of its development.

It is the feature of retrogressive differentiation or dedifferentiation that I wish particularly to recall here. The fact that certain areas of cartilaginous tissue'revert to an earlier embryonic type and are subsequently redifferentiated into a tissue of a Widely different histological character, is very clearly shown in the case of the otic capsule, and is a factor of great embryological significance. Such a process of retrogressive change, combined with redifferentiation of the same tissue, greatly in— creases the facilities for and the range of certain structural adjustments that occur in many regions in the development of the human embryo.

1 Streeter, G. L., 1917. The factors involved in the excavation of the cavities in the cartilaginous capsule of the ear in the human embryo. Amer. Jour. Anat.,


Another instance of dedifferentiation has recently been pointed out by Kunitomo? This writer has published the results of a careful study of the tail region in alarge number of human embryos, representing the period of greatest development of the caudal appendage, and also the later period of its gradual reduction. He shows that in very young specimens the spinal cord reaches the extreme tip of the tail and throughout its length is quite uniform in structure. Somewhat later (11 to 15—mm. stage) it can be divided at about the level of the thirty-second vertebra into two parts—a cranial or main part, having a Wide central canal and thick walls in which can be recognized well-developed mantle and marginal zones, and a caudal slender part, having a narrow canal with walls consisting only of an ependymal zone. Kunitomo shows that it is this caudal atrophic portion that eventually forms the filum terminale. The main part lying cranial to the thirty-second vertebra undergoes uninterrupted and progressive differentiation, whereas the portion caudal to this undergoes regressive changes and, with the exception of the extreme tip, finally becomes converted into a fibrous strand, the tip forming the coccygeal medullary vestige. This, therefore, is another instance in which an absorptive adjustment is brought about by the reversion of the tissue to an earlier embryonic type with a certain amount of subsequent redifferentiation.

Kunitomo further calls attention to the fact that in the formation of the filum terminale, in addition to the dedifferentiation of the caudal end of the medullary tube, there is also the mechanical disproportion between the growth of the medullary tube and that of the vertebral column. How much of one and how much of the other of these two factors is responsible for the further development of the filum terminale Was not determined by him. It has occurred to the writer that this question could be answered by the determination of‘the elongation of the nerve

2 Kunitomo, K., 1918. The development and reduction of the tail and of the caudal end of the spinal cord in the human embryo. Contributions to Embryology, vol. 8, Publication No.‘ 271, Carnegie Inst. of Wash. ‘



Cite this page: Hill, M.A. (2024, March 29) Embryology Paper - Factors Involved In The Formation Of The Filum Terminale. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Factors_Involved_In_The_Formation_Of_The_Filum_Terminale

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