274 THE RHOMBENCEPHALON. 



gives off the superior fillet (lemniscus superior} which terminates 

 in the superior quadrigeminal colliculus. The medial fillet ends 

 in the lateral nucleus of the thalamus (Fig. 47). Interruption of 

 the medial lemniscus causes ataxia on the opposite side. 



(2) Lateral Fillet. (Lemniscus lateralis). The lateral fillet 

 forms a link in the special sense, auditory path (Fig. 89). As 

 stated on page 160 it is but the longitudinal continuation of the 

 corpus trapezoideum and the medullary striae. It takes form 

 near the middle of the pons, where the fibers of the trapezoid body 

 bend- upward to a longitudinal direction; and it runs just lateral 

 to the medial fillet (Figs. 86 and 87). Very soon it becomes sepa- 

 rated from the medial fillet by the brachium conjunctivum of the 

 cerebellum. It runs dorso-medially over the conjoined brachium 

 to the inferior colliculus of the corpora quadrigemina, where a 

 few of its fibers end ; but the greater number are continued through 

 the brachium inferius to the medial geniculate body. The chief 

 origin of the lateral fillet is found in the opposite cochlear nuclei, 

 though some of its fibers rise in the nucleus of the corpus trapez- 

 oideum, the superior olivary nucleus, and the nucleus of the 

 lateral fillet, which constitute partial relays in the auditory path. 

 It is also true that a few fibers enter the lateral fillet from the 

 cochlear nuclei and nerve of the same side; they are supposed to 

 decussate near or in the quadrigeminal bodies and terminate in 

 the opposite inferior colliculus. Destruction of the lateral fillet 

 causes deafness, almost complete, in the opposite ear. 



(3) The spino-thalamic tract occupies the lateral part of 

 the formatio reticularis where it is intermingled with the anterior 

 ascending cerebello-spinal tract (Figs. 87 and 88). As already 

 stated, it rises in the spinal cord from the basal gray substance 

 of the anterior columna and from the terminal nuclei of common 

 sensory cerebral nerves in the medulla and pons. The spino- 

 thalamic tract ends in the lateral nucleus of the thalamus. It 

 conducts impulses of the tactile, pain and temperature senses. 



(4) The anterior ascending cerebello-spinal tract has the 

 same spinal origin and function as the spino-thalamic tract and 

 the same course up to the isthmus rhombencephali (Figs. 87 and 

 88). There, it bends backward, medial to the brachium con- 



