THE DEVELOPMENT OF THE NUCLEI PONTIS AND 

 THE NUCLEUS ARCUATUS IN MAN 



CHARLES R. ESSICK 



From the Anatomical Laboratory of The Johns Hopkins University 



TWELVE FIGURES 



The following paper shows the origin of the gray matter found 

 on the ventral surface of the adult rhombencephalon from the 

 'Rautenlippe' or rhombic lip, along its attachment to the medulla, 

 and the path of migration of the cells formed here to the position 

 characteristic of the fully developed brain. Almost all of the 

 cells of the arcuate and pontine nuclei arise by karyokinetic divi- 

 sion around the attachment of the roof of the fourth ventricle 

 and then wander to their proper places. The pathwaj^ of this 

 cellular migration proves to be a very superficial one, remarkable 

 both for its constancy and its definite limits. The arcuate nucleus 

 forms by a migration over the surface toward the ventral median 

 fissure; the pontine nuclei choose a path which corresponds in 

 every detail to the fibro-nuclear mass which I described for the 

 adult as the corpus ponto-bulbare. 



It is well known that all of the nuclear material in the central 

 nervous system is derived from that portion of the ectoderm which 

 closes in to form the neural tube; and our knowledge of the exact 

 manner of this cellular distribution is due mainly to the re- 

 searches of His. This author has pointed out that all of the nerve 

 cells in the central nervous system first passed through the stage 

 of neuroblasts and in their development are usually wont to leave 

 the place of their origin so as to enter into the formation of the 

 gray matter at a distance. The newly formed gray masses may : 

 (1) remain in the neighborhood of the matrix, e.g., motor and 

 arcuate cells of the spinal cord, or, (2) pierce the substance of 

 the medullary tube in a radial direction and collect on the surface 

 into an independent layer. Such wandering of cells from the 



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