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7 
INTERNAL STRUCTURE OF THE MEDULLA. 455 
tract, and which receives the name of the anterior basis-bundle. While the decus- 
sation is going on the anterior basis-bundle is thrust aside, and, sinking from the 
surface, it takes up its position as a flattened band-hke strand on the outer side of 
the gradually increasing pyramid (Fig. 537). When the decussation is completed 
this strand is seen to he close to the median plane on the dorsal aspect of the 
pyramid, where it is separated from its fellow of the opposite side by the median 
raphe alone (Fig. 358). In the upper part of the medulla it approaches still nearer 
to the dorsal surface and appears to form the greater part of a strand, which is 
termed the posterior longitudinal bundle (Figs. 340 and 341). The detached head 
of the anterior horn of gray matter of the cord, as it is traced upwards, is observed 
to cling closely to its original relationship with the anterior basis-bundle. It is 
apphed to the outer side of this strand, and, gradually becoming smaller, finally 
disappears at the level of the lower part of the inferior olivary nucleus. 
Cuneate and Gracile Strands, with their Nuclei.—As the funiculus gracilis 
and the funiculus cuneatus of the posterior column of the cord are traced up 
into the medulla they seem to increase in bulk, and in transverse sections they 
assume the form of massive wedge-shaped strands, quite distinct from each other. 
When the decussation of the pyramids is fully established they change their shape. 
They increase in width and lose considerably in depth, and consequently the 
transverse diameter of the area which they occupy becomes greater. As a result 
of this, they push outwards the posterior horn of gray imatter to such a degree 
that very soon it comes to lie transversely and in the same straight line with 
its fellow of the opposite side (Figs. 356 and 337). The substantia gelatinosa 
Funiculus gracilis 
Gracile nucleus 
Funiculus cuneatus 
Cuneate nucleus 
Accessory cuneate 
nucleus 
Spinal root of fifth 
nerve 
Substantia 
gelatinosa 
Rolandi 
Formatio 
Internal arcuate reticularis 
fibres 
Anterior basis- 
Anterior basis- bundle 
bundle 
Mesial olivary 
Decussation of 
nucleus 
fillet 
Olivary nucleus 
Arcuate nucleus 
Fic. 338.—SECTION THROUGH THE CLOSED PART OF HUMAN MEDULLA IMMEDIATELY ABOVE THE 
DECUSSATION OF THE PYRAMIDS. 
Rolandi, at the same time, becomes increased in quantity and presents a horse- 
shoe-shaped outline in transverse section. It clasps within its concavity the 
somewhat reduced head of the posterior horn, and forms with it a conspicuous 
circular mass of gray matter which lies close to the surface, and produces upon it 
the bulging termed the funiculus and tubercle of Rolando. The basal portion of 
the posterior horn of gray matter remains upon the dorsal and lateral aspect of the 
central canal, and forms a portion of the central gray mass of the closed part of 
the medulla; but very soon the neck of the horn is invaded by bundles of fibres 
