Paper - The Peripheral Nervous System in the Human Embryo at the End of the First Month (10 mm)
Embryology - 20 Apr 2024    Expand to Translate
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Streeter G.L. The Peripheral Nervous System in the Human Embryo at the End of the First Month (10 mm) 8 Historic Embryology Papers
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The Peripheral Nervous System in the Human Embryo at the End of the First Month (10 mm)
By
P1‘ofcssm' of Anatomy, Um‘vcrsity of Michigan-, Ann Arbor.
(With 3 Plates And 1 Text Figure.)
The period of development under consideration represents the completion of what we may call the primary stage in the growth of the nervous system. The primary neurones forming the peripheral nerves are by the end of the first month well laid down; all their chief peripheral branches and plexuses are indicated, a11d centrally the nerve roots can be traced to their distribution in the brain and spinal cord, where the nuclei of the motor roots can be outlined and the sensory roots can be recognized as definite bundles extending up and down in the wall of the neural tube. The higher neurone systems, however, are still in a most rudimentary state, and in sections through the brain and cord at this time we see only the primary apparatus differentiated. Such co—ordinating centers as the pons, olive and cerebellum are still undeveloped, and the forebrain is not much more than an undifferentiated thin-Walled tube. It can thus be seen that the period with which we are dealing represents a definite stage in the growth of the nervous system, the stage of the primary brain, and a stage which is of particular importance for a proper conception of the embryology of this system.
A general view of the nervous system as it exists in embryos at
the end of the first month is represented on Plate I. It can be seen
that the‘ reconstruction shown there corresponds in age almost exactly
with the well known His reconstruction of his embryo KO of 10.2 mm.
N1. That investigator early recognized the significance of the stage
of the primary brain. However, since His, ’88, published his monograph and description of the embryo KO there have been introduced
many improvements in the methods of work, and before all others
should be mentioned the Born wax plate procedure. It is with such aid and by means of the increased supply of available embryos that it
was possible by Lewis, ’02, to elicit further detail and obtain greater
completeness in our conception of the formation of the brachial plexus
and the development of the nerves of the arm, and Bardeen, ’O7, the
nerves of the leg, and myself the nerves of the occipital region (Streeter,
’04). With this in mind it seemed desirable to go over the same ground
covered by His in his reconstruction of the embryo K0 With the purpose
of bringing out the same structures with more accurate detail and in more plastic form, and at the same time to incorporate the results of
the Work of the investigators just mentioned.
Some of the features brought out by this study with regard to the
cranial nerves were reported at the Chicago meeting of the Association
of American Anatomists (Streeter, ’08). It is the purpose of the
present paper to include the whole peripheral nervous system of the same
embryo.
Material and Methods
The embryo on which this study is based constitutes No. 3 of Professor Huber’s (lolleetion, and was kindly loaned by him for this purpose. After fixation in alcohol the specimen measured 10 mm. greatest length. Its estimated age is 31 days. Unfortunately there was no clinical history obtainable. The embryo is cut in a series of 5 micra sagittal sections, and the tissues are in an excellent state of preservation. The description and drawings are based in part on wax plate models and in part on profile reconstructions made in the usual way by superimposing transparent papers.
Brain and Spinal Cord
The general form of the brain and spinal cord and their relation to the body outlines is shown in Plate I. The spinal cord is largest in the cervical region, and from there slowly tapers down, being somewhat larger again in the lumbar region, and finally abruptly tapers oif at the coccyx. In transverse section the cord possesses a trapezoid outline with rounded corners, the width of the Ventral half being a little greater than that of the dorsal half. A large ventricle or central canal extends throughout its whole length. By the lanceolate border of this canal the cord is divided on each side of the median line into an alar and basal plate.
Toward the head the spinal cord enlarges and gradually merges into
the rhombencephalon. In this transition the basal plates become thicker,
Cite this page: Hill, M.A. (2024, April 20) Embryology Paper - The Peripheral Nervous System in the Human Embryo at the End of the First Month (10 mm). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_Peripheral_Nervous_System_in_the_Human_Embryo_at_the_End_of_the_First_Month_(10_mm)
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