SENSE AREAS AND ASSOCIATION AREAS. 



191 



inferior peduncle of the same side; but others, passing ventrally, 

 cross the mid-line as the internal arciform fibers, which form a 

 conspicuous feature in the tegmental region of sections of the 

 medulla at this level. This crossing occurs mainly just in front 

 of that is, cephalad to the pyramidal decussation, forming thus 

 a sensory decussation, which explains the crossed sensory control, 

 as the pyramidal decussation explains the crossed motor control 

 of the cerebrum in relation to the body. After this decussation 

 the sensory fibers form a longitudinal bundle on each side known 

 as the median fillet, lemniscus, or laqueus, which in the pons lies 

 just dorsal to the pyramidal fibers. 



The fillet fibers may be traced forward as far as the anterior collie- 



Fig. 86. Cross-section through midbrain (Kolliker) to show the position of the fillet (L, L): 

 Nr, The red nucleus ; Sn, the substantia nigra ; Pp, the crus. 



ulus of the corpora quadrigemina and the thalamus (see Fig. 86), 

 and some are said to continue directly into the cerebrum by way of 

 the posterior limb of the internal capsule to end in the parietal lobe 

 posterior to the fissure of Rolando. Those neurons that end in the 

 midbrain and thalamus are continued forward by a third neuron, 

 which ends in the parietal lobe in the same region (see Fig. 77, C). 

 On its way through the medulla and pons the fillet tract is believed 

 to receive accessions of sensory fibers from the sensory nuclei of the 

 cranial nerves of the opposite side. The course of the fillet has been 

 traced by various means, but especially by the method of myeliniza- 

 tion during embryonic life and by degeneration consequent upon 

 long-standing disuse. As was stated in the section upon nerve de- 



