THE MAMMALIAN NERVOUS SYSTEM 75 



XI; Morris ('14), pp. 931, 932, Fig. 661, p. 837, Fig. 663, p. 839; 

 Villiger ('12), Fig. 162, p. 175). 



88. Correlation fibers of the medulla oblongata. — Afferent nerve- 

 fibers enter the medulla oblongata by the sensory roots of the V 

 to X cranial nerves and by certain tracts from the spinal cord. 

 Some of these fibers effect secondary connections with the cere- 

 bellum as described below; some of the other connections are as 

 follows: 



The peripheral general cutaneous fibers from the head are dis- 

 charged into the chief sensory and spinal V nuclei. The axons 

 of the neurons of these nuclei in part connect with the various 

 motor nuclei of the brain-stem for local reflexes, and in part 

 ascend to the thalamus through the trigeminal lemniscus, as 

 already mentioned. 



The central connections of the general proprioceptive fibers 

 of the head are unknown. Probably the mesencephalic V 

 nucleus is related to this system. 



The special proprioceptive fibers from the labyrinth are re- 

 ceived by the vestibular nuclei, as already described; the axons 

 of these cells reach the various motor nuclei of the bulb, the 

 cerebellum (through the vestibulo-cerebellar tract) and the 

 spinal cord (through the vestibulo-spinal tract). The fasciculus 

 longitudinalis medialis is an important correlation tract for this 

 system (see Section 92). 



The chief central pathway from the cochlear nuclei is the 

 lateral lemniscus already studied; but in addition to this there 

 are manifold reflex connections between these nuclei, the nuclei 

 of the trapezoid body, the superior olives, the nuclei of the 

 lateral lemniscus, and the inferior colliculus on one hand and the 

 motor nuclei of the bulb and spinal cord on the other hand. 

 The spinal connection is chiefly through the tecto-spinal tract of 

 the cord (Herrick ('15), Fig. 59) . 



Visceral reflexes may be effected by short and very simple 

 connections between the nucleus of the fasciculus solitarius and 

 the motor nuclei of the bulb. There is also a visceral lemniscus 

 conducting visceral impulses upward to the diencephalon, but 

 the course of these fibers in the human brain is unknown. 



89. The reticular formation (see Herrick ('15), Figs. 69, 73, 

 81, and 83) . — In addition to the direct and relatively simple con- 



