THE MEDULLA OBLONG ATA AND CEREBELLUM 157 



with the motor nuclei of the medulla oblongata, these connec- 

 tions being effected through the reticular formation (Figs. 69, 

 73) ; (2) descending reflex connections with the motor centers of 

 the spinal cord, by way of the bulbo-spinal tracts (such as the 

 vestibulo-spinal tract, Fig. 59); (3) connections with the cere- 

 bellum (this applies only to such functional systems as have pro- 

 prioceptive value, of which the vestibular nerve from the semi- 

 circular canals of the ear is the most important) ; (4) connections 

 with the thalamus and (after a synapse here) with the cerebral 

 cortex. 



The fibers of the type last mentioned comprise the bulbar 

 lemniscus (Figs. 64, 77) ; of this there are several distinct parts, 

 two of which require special mention, viz., the trigeminal lem- 

 niscus and the lateral lemniscus. The skin of the head is inner- 

 vated chiefly by the trigeminal nerve (V pair) and the fibers of 

 this type terminate in the general somatic sensory area (known as 

 the chief sensory V nucleus and the spinal V nucleus or gelatinous 

 substance of Rolando, Figs. 71-74). After a synapse in this 

 area the fibers of the trigeminal lemniscus cross to the opposite 

 side and ascend to the thalamus in a pathway distinct from all 

 other lemniscus fibers (see p. 180 and Figs. 64, 75, 77, 78, 81). 



The lateral or acoustic lemniscus comprises by far the largest 

 component of the bulbar lemniscus complex. Its fibers arise 

 from the terminal nuclei of the cochlear nerve (VIII pair, Fig. 

 71), cross at once to the opposite side of the brain, and ascend 

 to the midbrain (Fig. 75). Some of these fibers continue di- 

 rectly to the thalamus, where they end in the medial geniculate 

 body (Fig. 77); others terminate in the roof of the inferior 

 colliculus of the midbrain. After a synapse here and various 

 reflex connections, the nervous impulse may be carried forward 

 to the medial geniculate body of the thalamus by way of the 

 brachium quadrigeminum inferius (Figs. 75, 86). (Regarding 

 this system see further on pp. 195-203.) 



In fishes there is an ascending secondary visceral and gusta- 

 tory tract, or visceral lemniscus, from the visceral sensory area to 

 the midbrain (p. 246) ; this tract no doubt occurs in the human 

 brain also, though its exact course has never been demonstrated. 



Having now reviewed cursorily the primary sensory and motor 

 centers of the medulla oblongata, we must next examine some of 



