54 CHARLES R. ESSICK 



form. This is not true in the arcuate formation where the nuclei 

 are still very densely staining and there is very little protoplasm 

 in the bodies. In No. 509 (188 mm.), however, the protoplasmic 

 body is represented by a clear unstained area around a pale 

 vesicular nucleus. Here it is possible to speak of young ganglion 

 cells with certainty although most of the elements are still undif- 

 ferentiated. 



To conclude, then, we have in the rhombic lip or 'Rautenlippe' 

 of His a common ancestor for the olive, pontine nuclei and arcuate 

 nuclei — the nuclei pontis being formed by a migration through a 

 restricted pathway, the corpus ponto-bulbare; the nuclei arcuati 

 along with part of the olive by a superficial migration over the 

 ventral surface of the medulla. 



BIBLIOGRAPHY 



Blake, J. A. 1900 The roof and lateral recesses of the fourth ventricle con- 

 sidered morphologically and embryologically. Jour. Comp. Neur., 

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Essick, C. R. 1907 The corpus ponto-bulbare — a hitherto undescribed nuclear 

 mass in the human hind brain. Amer. Jour. Anat., vol. 7. 

 1909 On the embryology of the corpus ponto-bulbare and its relation 

 to the development of the pons. Anat. Rec, vol. 3. 



Flechsig, P. 1876 Die Leitungsbahnen in Gehirn und Riickenmark des Men- 

 schen. Leipzig. 



His, W. 1891 Die Entwicklung des menschlichen Rautenhirns vom Ende des 

 ersten bis zum Beginn des dritten Monats. Leipzig. 

 1904 Die Entwicklung des menschlichen Gehirns wahrend der ersten 

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Orzechowski, K. 1908 Ein Fall von Missbildung des Lateralrecessus. Ein 

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Streeter, G. L. 1904 The development of the cranial and spinal nerves in the 

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 1907 On the development of the membranous labyrinth and the acous- 

 tic and facial nerves in the human embryo. Amer. Jour. Anat., vol. 6. 

 1912 The development of the nervous system. Manual of Human 

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Tiedemann, F. 1816 Anatomie und Bildungsgeschichte des Gehirns in Foetus* 

 des Menschen. Niirnberg. 



