Histogenesis Of The Spinal Cord And Spinal Ganglia

  • Santiago Ramón y Cajal


The spinal cord represents a fold of the ectoderm, and its elements merely represent transformed epithelial cells. The primordial phases of this transformation are known today from the fundamental observations of His (1879, 1883, 1886, 1887, 1889) made preferentially in the human embryo.


Chick Embryo Growth Cone Ventral Root Germinal Cell Connective Tissue Cell 
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  1. 1.
    It is in the embryology section of this study that Kupffer states the fundamental thesis on the origin of nerve fibers.Google Scholar
  2. 2.
    Some authors, however, attribute a proliferative capacity to nerve cells of small size. Thus, Levi (1898), who has studied the healing of cerebral wounds in the guinea pig, reports to have seen mitoses in small pyramidal cells, but not in the large ones or in motor cells of the spinal cord, i.e. in neurons with centralized chromatin; which, on passing, confirms our opinion that the centralization of the chromatin implies the incapacity to divide.Google Scholar
  3. 3.
    We formulated this doctrine already in our second work on the cerebellum (Cajal, 1890b; see also Cajal, 1893c).Google Scholar
  4. 4.
    Golgi recognized well the general pattern of the epithelium which he described as formed by radial fibers extending from the ependyma to the pia where they would end either by a conical enlargement or by fine threads inserted on capillaries. Secondary branchlets would emerge in the course of radial fibers, terminating in part on vessels. This scholar did not study, however, the morphology of the epithelium in different spinal radii, nor its histogenetic relationships with the neuroglia. Also Falzacappa (1889) apparently impregnated, at least partially, the primitive epithelium of birds embryos, according to a brief mention in his report.Google Scholar
  5. 5.
    [We believe that the intercellular anastomoses recently described by Held in the trigeminal ganglion of the duck embryo at the 56th incubation hour, are just products of the coupling of irregular appendages of certain neuroblasts. In our neurofibrillar preparations made from chick embryos of the same incubation period, the immense majority of neurons show indeed a frankly bipolar pattern.]Google Scholar
  6. 6.
    [However, radial interstices between ependymal cells could also play a role in determining this orientation.]Google Scholar


  1. a.
    Fig. 233.— a, cell with beginning of a central process; b, c, same as A, i.e. neurons in apolar stage.Google Scholar
  2. b.
    Fig. 234.— d, ganglion cell in bipolar phase.Google Scholar
  3. c.
    Fig. 236.— a, unidentified; b, intranuclear rod; c, axoplasmic substance.Google Scholar
  4. d.
    Fig. 238.— E, bipolar cell with very incipient central process.Google Scholar
  5. e.
    Fig. 239.— C, dorsal horn bundle; c, same as b, i.e. cone bound for the dorsal horn bundle.Google Scholar
  6. f.
    Fig. 242.— A, normal neuroblast extending the peripheral process toward the dorsal horn bundle; C, same as D, E, i.e. neuroblast re-entering the ependyma; F, faulty pathway leading the growth cone to the columnar and nuclear layers; H, unidentified; c, probably commissural neuroblasts.Google Scholar
  7. g.
    Fig. 243.— F, fibers of the medial longitudinal fasciculus; a, other looping trochlear nerve fibers.Google Scholar
  8. h.
    Fig. 246.— d, motor nerve; f, muscle.Google Scholar
  9. i.
    Histologie reads in error Fig. 269E instead of Fig. 246E, which is the equivalent of Fig. 242E of the present version.Google Scholar
  10. j.
    Fig. 247.— a, spherule ending; b, two new branches ending in conical swellings.Google Scholar
  11. k.
    Fig. 249.— a, zone of entry and bifurcation of dorsal root fibers; e, mitotic cell.Google Scholar
  12. l.
    *Fig. 250.— E, white matter of the dorsal funiculus; c, unidentified.Google Scholar
  13. mThe risk taken by extrapolating adult morphology from that of early developmental stages is clear in the behavior of a certain kind of striatal neurons, which having spines on their dendrites in the early postnatal period (and such was the material used by Cajal in his descriptions of the corpus striatum in Volume III), loose the spines in later periods [Di Figlia, Pasik, Pasik (1980) J Comp Neurol 190: 303-332].Google Scholar
  14. nFig. 251.— c, collaterals of the lateral funiculus.Google Scholar
  15. oTextura reads in error Fig. 192a instead of Fig. 81a, which is the equivalent of Fig. 109a of the present version.Google Scholar
  16. pSee annotations a and b in Chapter IX for discussion on myelin formation.Google Scholar
  17. qFig. 254.— B, ventral horn; C, inner zone or epithelial wall.Google Scholar
  18. rFig. 255.— a, soma and nucleus of epithelial cell.Google Scholar
  19. sFig. 256.— E, surface of central cavity with cilia of ependymal cells.Google Scholar
  20. tFig. 257.— C, early stage with the soma still attached to the ependymnal wall; E, same as D, i.e. astroblast.Google Scholar
  21. uFig. 258.— D, more mature neuroglia of the gray matter; G, neuroglia of the white matter with remnants of ependymal processes, and peripheral process attached to the pia.Google Scholar
  22. vFig. 262.— a, nucleus of satellite cell; b, mitotic cell; c, dense neurofibrillar bundle in a process of a cell at the bipolar state.Google Scholar
  23. wAfter much debate, Cajal’s view of the origin of the single stem of unipolar ganglion cells from an elongated portion of the soma, and not from the fusion of the original two processes, has received ample confirmation by both transmission and scanning electron microscopy [Takahashi and Ninomiya (1987) Progr Neurobiol 29: 393-410].Google Scholar
  24. xFig. 266.— C, simple growth cone; D, F, G, bifurcating growth cones.Google Scholar
  25. yFig. 267.—e, mesodermic cell.Google Scholar
  26. zThe ectodermic origin of Schwann cells was eventually demonstrated [Plenk (1934) Ztschr mikr-anat Forsch 36: 191-214].Google Scholar
  27. aa.
    Fig. 270.— e, unidentified; f, g, nuclei of mesodermic cells.Google Scholar
  28. bb.
    The discovery of the oligodendrocyte [Rio Hortega (1921) Bol Real Soc Espan Hist Nat 21: 63-92], and its role in myelin formation of central nervous system fibers is a much later event. See annotation b in Chapter IX.Google Scholar
  29. cc.
    Figs. 256 and 257 are from human embryo and newborn mouse, repectively. ddHistologie reads in error neuroblasts instead of neurodesms.Google Scholar

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© Springer-Verlag Wien 1999

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  • Santiago Ramón y Cajal

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