SPINAL CORD AND COMMENCEMENT OF MEDULLA OBLONG ATA. Ill 



Fig. .106 represents a section through the cervical medulla 

 about opposite the point of emergence of the first spinal nerve. 

 Its general appearance reminds us, on the whole, of the sections 

 wind i we have before examined. We must notice three points 

 in particular, because they differ from what we have hitherto 

 seen. One is the peculiar shape of the posterior horn. It con- 

 sists only of a thin " neck " united to its most dorsal portion, 

 which at this level is markedly thickened by admixture with 

 the substantia gelatinosa. This thickened portion is called the 

 "head of the posterior horn." The substantia gelatinosa is 



FIG. 106. 

 Section through the uppermost portion of the cervical cord. 



Hinterhorn, Post. horn. Sr.itenhurn, Lateral horn. 



permeated by innumerable fine fibrils, which may possibly have 

 their origin in it. All these pass to the region lying external to 

 the substantia gelatinosa and form a fasciculus, which extends 

 to the periphery of the spinal cord and presents a somewhat 

 crescentic appearance on cross-section. This fasciculus ascends 

 far up into the pons, to the point where the trigeminus is given 

 off, and emerges along with the fibres of the latter. It is called 

 the ascending root of the fifth nerve. In all the sections which 

 I show vou from now on we shall see this crescent of nerve- 



v 



fibres and the substantia gelatinosa lying median to it. 



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