INTEKNAL STKUCTUKE OF MEDULLA OBLONGATA AND PONS. 559 



3 it is traced upwards, is observed to cling closely to its original relationship 

 dth the fasciculus anterior proprius. It is applied to the lateral side of this strand, 

 ad, gradually becoming smaller, finally disappears at the level of the inferior part 

 f the inferior olivary nucleus. 



Cuneate and Gracile Fasciculi, with their Nuclei. As the fasciculus gracilis 

 ad the fasciculus cuneatus of the posterior funiculus of the spinal medulla are 

 aced up into the medulla oblongata they seem to increase in bulk, and in trans- 

 srse sections they assume the form of massive wedge-shaped strands, quite 

 istinct from each other. They increase in width and lose considerably in depth, 

 id consequently the transverse diameter of the area which they occupy becomes 

 reater. As a result of this, and also owing to the removal of the lateral 

 irebro-spinal tract from the lateral funiculus of the spinal medulla immediately 

 L front, the posterior column of gray matter is gradually rotated forwards and 

 >mes to lie transversely and in the same straight line with its fellow of the 



Central canal 



isciculus anterior 

 proprius 



i Decussation of 

 inniscus inedialis 



Inferior 

 olivary nucleu 



Funiculus gracilis 



Gracile nucleus 



Funiculus cuneatus 

 x Cuneate nucleus 



Accessory cuneate 

 nucleus 



Tractus spinalis of 

 fifth nerve 



Nucleus tractus 

 spinalis nervi 

 trigemini 



Fasciculus 

 anterior proprn 



Medial olivary 

 nucleus 



Pyramid 



Arcuate nucleus covered 

 superficially by external 

 arcuate fibres 



FIG. 491. SECTION THROUGH THE CLOSED PART OF THE HUMAN MEDULLA OBLONGATA IMMEDIATELY 

 ABOVE THE DECUSSATION OP THE PYRAMIDS (Weigert-Pal specimen). 



posite side (Figs. 490 and 491). The substantia gelatinosa, at the same time, 



, comes increased in quantity and presents a horseshoe-shaped outline in trans- 



rse section. It clasps within its concavity the somewhat reduced head of the 



isterior column, and forms with it a conspicuous circular mass of gray matter 



ich lies close to the surface, and produces upon it the bulging termed the 



berculum cinereum. The basal portion of the posterior column of gray matter 



Lains upon the dorsal and lateral aspect of the central canal, and forms a 



iioii of the central gray mass of the closed part of the medulla oblongata ; but 



oon the neck of the column, which at this level is greatly reduced owing to 



* absence of entering posterior nerve-roots, is invaded by bundles of fibres 



ich traverse it in different directions and convert it into a forma tio reticularis. 



is means the rounded head of the posterior column becomes cut off from the 



-1 gray matter, and from this point upwards it remains as an isolated gray 



uumn intimately associated with the spinal root of the trigeminal nerve. It has, 



, become the nucleus tractus spinalis nervi trigemini. 



The gracile and cuneate nuclei are seen in their most typical form in sections 

 the level of the decussation of the pyramids (Figs. 489 and 490). The gracile 



