394 W. H. GASKELL. 



themselves are no longer so closely packed together as in the 

 younger stages, so that the appearance of carmine preparations 

 of the brain in the animal after transformation is as is repre- 

 sented in figs. 9, 10, PI. XXV. This transformation of a 

 columnar cell into a tailed cell which forms part of the support- 

 ing tissue in, at all events, the substantia centralis gela- 

 tinosa, the shrinking of the cell body, and the disappearance 

 of a marked limiting layer at the base of the columnar epithe- 

 lial cells, are due mainly to the fatty degeneration already 

 described ; so, also, I imagine that the lining cells themselves 

 are no longer so crowded together, because some of them 

 have shrunk to such an extent that they no longer form properly 

 developed cells, but present rather the appearance of strands 

 and shreds of tissue. 



In so far, then, as the columnar cells of the old stomach wall 

 assist in forming supporting tissue for the nervous elements 

 of the brain, I am not prepared to say more than that they 

 assist in forming the supporting tissue of the substantia 

 centralis gelatinosa by their elongation into long-tailed 

 processes in consequence of a process of fatty degeneration 

 which they have undergone. 



(2) The Formation of the Raphe. — Further, the result 

 of this breaking down of protoplasm into fat brings about not 

 only the formation of a lining epithelium with long processes 

 directed into the nervous matter, but also causes a raggedness 

 in that part of the cells which is turned towards the lumen, 

 so that wherever the cavity is closed by the coming together 

 of its walls, as is the case in the medulla oblongata, the original 

 lumen is bridged over by a ragged reticulum, the interlacement 

 of the fibres of which tend to permanently close the lumen ; 

 in other words, owing to the degenerative changes going on, 

 the walls of the original cavity become, so to say, stitched 

 together in the middle line, and in this way the raphe, 

 which is so characteristic of the epichoidal portion of the 

 brain, is formed. 



It is especially instructive to notice that throughout the 

 medulla oblongata the closed tube which forms the raphe. 



