158 INTRODUCTION TO NEUROLOGY 



the centers of correlation. As has already been indicated, all of 

 these centers are interconnected by correlation neurons similar 

 to those of the spinal cord (Figs. 60, 61). These neurons are 

 loosely arranged in the spaces between the sensory and motor 

 groups of nuclei, this tissue being termed the reticular formation 

 (this region is also called the tegmentum, see pp. 65, 127 and 

 Figs. 69, 74). But the chief centers of correlation of the brain 

 stem are found in specially enlarged nuclei of the midbrain and 

 thalamus, some of which are mentioned in the next chapter. 



In its more ventral parts the medulla oblongata contains a 

 number of large correlation centers and important conduction 

 pathways between remote parts of the brain. Of the former, the 

 largest are the inferior olives (Figs. 72, 73, 74), deeply buried 

 masses of gray matter arranged in the form of a hollow shell of 

 complex shape on each side of the median plane. The olives 

 receive fibers from the thalamus and spinal cord and discharge 

 into the cerebellum (olivo-cerebellar fibers of Fig. 72). Their 

 functions are unknown. 



The cerebellum has already been referred to as a great supra- 

 segmental mechanism of unconscious motor coordination. It 

 is connected with the underlying brain stem by three pairs of 

 stalks or peduncles, two of which join the medulla oblongata and 

 one the midbrain. The inferior peduncle (restiform body) 

 connects with the dorsal margin of the medulla oblongata and 

 carries fibers into the cerebellum from the spinal cord and ob- 

 longata. The middle peduncle (brachium pontis) connects 

 with the pons and most of its fibers convey impulses from the 

 nuclei of the pons to the cerebellum. The superior peduncle 

 (brachium conjunctivum) connects with the cerebral peduncle 

 in the floor of the midbrain and contains chiefly fibers which 

 descend from the cerebellum, cross the midplane under the 

 aqueduct of Sylvius, and terminate in or near the red nucleus 

 (Fig. 75, nucleus ruber). The internal structure and connec- 

 tions of the cerebellum will be further considered on page 186. 



Summary. The rhombencephalon includes the medulla 

 oblongata and cerebellum, that is, all parts of the brain below 

 the isthmus. All of the cranial nerves except the first four pairs 

 connect with the medulla oblongata. An analysis of the func- 

 tional components of the cranial nerves shows that they can 



