Book - Contributions to Embryology Carnegie Institution No.30

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Variability In The Spinal Column As Regards Defective Neural Arches (Rudimentary Spina Bifida)

By Theodora Wheeler

Of the Department of Embryology, Carnegie InslUulion of Washington.


With eleven figures.


Links: Carnegie Institution of Washington - Contributions to Embryology
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Introduction

Studies of minor variations arc continually being presented in biological fields. The reason for the persistent attention directed toward this line of study is not far to seek. To any observer the more or less frecjuent appearance of varied characteristics in form or function can not fail to suggest many perplexing questions as to the causes underlying such processes, and also as to their immediate and ultimate effects. As a consequence, some of the most valuable theories in the different branches of the natural sciences have been suggested, and are being worked out, by means of the evidence afforded by these variations. The theory of evolution, with all its ramifications, has been and is being developed along these lines. Since the beginning of the nineteenth century, especially, the attention centered about variations has been tremendous. Lamarck, Darwin, Mendel, and then Galton were really the first to get the upper hand in the study and treatment of variations, and more recently a rapidly enlarging group of workers in genetics have, by fresh methods, gleaned a most fruitful harvest in this field. The methods themselves have been most numerous and varied, and it is especially true of this subject that its history is to be found in the history of its methods. At first lax and slip-shod, they have gradually become, through the influence of the men just mentioned, thorough and accurate. Probably the chief ones in present use are the statistical and the experimental methods and their combinations. So, as time goes on, innumerable minutise and data are gathered on every side and made to serve their part in unraveling problems. A noteworthy instance of help afforded by such studies is the more fundamental idea which we now have of the biological conception of the normal or type. This very necessary standard, though even now far from finally understood, has developed in the minds of men from a very rigid concept into a far more plastic and adaptable principle, mainly through the insight gained by variation study.


Very often these studies may be applied with profit to specialized problems. An example of this is the frequent and rather interesting results obtained along morphological hnes in the higher animal forms in demonstrations of the persistence in postnatal life of earUer phases of development, which, as a rule, become changed or obliterated during the course of growth. The present investigation deals with the variabihty throughout the spinal column in respect to incomplete union of the posterior laminse of the vertebrae. Associated with this subject is the question of its relation to the pathological condition of spina bifida. The incomplete ossification of the adult vertebral spinous processes is also an example of a condition of delayed development which has been present throughout the spine at an earlier period.


The boiw closure of the posterior vertebral arches begins in the lumbar region, proceeding upward and downward from this point. In a model of the chondrocranium and cervical vertebrae of a 42 mm. embryo (No. 886, Carnegie Collection) made by Dr. C. C. Mackhn, the cartilaginous closure of the atlantal neural arches lags considerably behind that of the other cervical vertebrae, which evidence also substantiates this sequence in the cervical region. As is the case with other growth phenomena, there must be considerable variation in the time of completion of this process. According to Hennig (1880) the lumbar spinous processes are ossified by the third year. Macahster (1893) gives time of completion of the dorsal arch in the atlas as the fourth year, and Radlauer (1908) states that ossification of the sacral spinous processes, beginning with Si in the third year, is finally completed with S4 and Ss in the seventh year.


Incomplete closure of the sacrum has been the subject of numerous studies. In 1902 W. R. Smith noted the variation associated with left-sided sacraUzation of the fifth lumbar in a female Australian aboriginal sacrum, and more recently Radlauer (1908), Adolphi (1911), Frets (1914), and Wetzel (1915) have contributed considerable data on the subject. Radlauer studied 500 sacra, representing various races, from the University of Zurich and from several German collections. He found a completely open sacral canal in 5 per cent of the cases. He found also that closure of the hiatus sacralis occurred more frequently, (1) over the fourth and between the fourth and fifth sacral vertebra, 45.6 per cent; (2) over the third and between the third and fourth sacral vertebra, 27.4 per cent; and (3) over the fifth sacral vertebra, 14 per cent.


Adolphi (1911), working in Dorpat with 292 skeletons (234 male and 58 female), found an open sacral canal in 3.4 per cent of the males and 1.7 per cent of the females — a total of 3.08 per cent. In 50.3 per cent (48.7 per cent of males and 56.9 per cent of females) there were 4 sacral vertebrae closed; in 24.3 per cent (25.2 per cent of males and 20.7 per cent of females) 3 vertebrae were closed; while in 12 per cent of both males and females 5 vertebrae were closed.* In 12.7 per cent there was some degree of opening of the first sacral arch.* In a group of 203 specimens (161 male and 42 female), in which there were 5 and 6 vertebrae with no transitionally formed ones, he found that the hiatus sacralis reached to the third vertebrae in 26.6 per cent (28 per cent of the males and 21.4 per cent of the females) ; to the fourth vertebra' in 51.2 per cent (48.4 per cent of males and 61.9 per cent of females); and to the fifth vertebrae in 12.3 per cent (13 per cent of males and 9.5 per cent of females).



Content to be added----

Figures

Wheeler1920 fig05-11.jpg

Figures 5 to 11


Historic Disclaimer - information about historic embryology pages 
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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)


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Cite this page: Hill, M.A. (2019, November 18) Embryology Book - Contributions to Embryology Carnegie Institution No.30. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Contributions_to_Embryology_Carnegie_Institution_No.30

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