l6o THE CEREBRUM. 



Function. The fillet forms a segment in the direct sensory 

 tract. It carries spinal and cerebral impulses of the tactile and 

 muscular senses to the corpora quadrigemina and thalamus, 

 and auditory impulses to the inferior quadrigeminal colliculus. 



f L. Medialis -{ L. Superior. 

 Lemniscus < , T . ,. 

 { L. Laterahs 



Medial Fillet. (Lemniscus medialis, Figs. 47 and 48). The 

 fibers composing the medial fillet rise chiefly in the nucleus funiculi 

 gracilis and nucleus funiculi cuneati of the opposite side of the 

 medulla oblongata. They cross over in the fillet decussation 

 of the medulla; and, excepting a small bundle, terminate in the 

 lateral nucleus of the thalamus. Fibers are added from the 

 terminal nuclei of sensory cerebral nerves which cross the median 

 plane and enter the opposite fillet. Thus connected with all 

 common sensory nerves, and with the vestibular nerve, it enters 

 the mid-brain and divides into two parts. A small bundle of 

 fibers separating from the lateral part and running to the superior 

 quadrigeminal colliculus, forms the superior fillet. It associates 

 ocular movements with sensations from cerebral and spinal nerves. 

 The medial fillet continues to the lateral nucleus of the thalamus, 

 bearing impressions of the tactile and the muscular sense. From 

 the thalamus the impulses are carried by the cortical fillet to the 

 somaesthetic area of the cortex. 



The lateral fillet (lemniscus lateralis) forms an oblique 

 ridge on the lateral border of the tegmentum (Fig. 44). It trends 

 upward and inward over the brachium conjunctivum to the infe- 

 rior quadrigeminal colliculus where some of its fibers terminate. 

 A few fibers continue to the superior colliculus. Its function is 

 auditory conduction. It rises chiefly from the ventral and lateral 

 parts of the cochlear nucleus (principally the opposite one) and 

 ends in the inferior quadrigeminal colliculus. The greater 

 number of its fibers cross through the trapezoid body and medul- 

 lary striae, some are uncrossed. It undergoes partial relay in the 

 nucleus of the superior olive and nucleus of the trapezoid body on 

 both sides and the nucleus of the lateral fillet on the same side. 



The lateral fillet is only partially relayed in the inferior col- 



